Slow catchup of 2PC (twophase) transactions on replica in LR

From 549f809fa122ca0842ec4bfc775afd08feee0d80 Mon Sep 17 00:00:00 2001
From: Vitaly Davydov <v.davydov@postgrespro.ru>
Date: Tue, 27 Feb 2024 14:02:23 +0300
Subject: [PATCH] Add asynchronous commit support for 2PC

---
 src/backend/access/transam/twophase.c | 111 +++++++++++++++++++++++++-
 1 file changed, 108 insertions(+), 3 deletions(-)

diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index c6af8cfd7e..52f0853db8 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -109,6 +109,8 @@
 #include "utils/memutils.h"
 #include "utils/timestamp.h"
 
+#define POSTGRESQL_TWOPHASE_SUPPORT_ASYNC_COMMIT
+
 /*
  * Directory where Two-phase commit files reside within PGDATA
  */
@@ -163,6 +165,9 @@ typedef struct GlobalTransactionData
 	 */
 	XLogRecPtr	prepare_start_lsn;	/* XLOG offset of prepare record start */
 	XLogRecPtr	prepare_end_lsn;	/* XLOG offset of prepare record end */
+	void*       prepare_2pc_mem_data;
+	size_t      prepare_2pc_mem_len;
+	pid_t       prepare_2pc_proc;
 	TransactionId xid;			/* The GXACT id */
 
 	Oid			owner;			/* ID of user that executed the xact */
@@ -427,6 +432,9 @@ MarkAsPreparing(TransactionId xid, const char *gid,
 
 	MarkAsPreparingGuts(gxact, xid, gid, prepared_at, owner, databaseid);
 
+	Assert(gxact->prepare_2pc_mem_data == NULL);
+	Assert(gxact->prepare_2pc_proc == 0);
+
 	gxact->ondisk = false;
 
 	/* And insert it into the active array */
@@ -1129,6 +1137,8 @@ StartPrepare(GlobalTransaction gxact)
 	}
 }
 
+extern bool IsLogicalWorker(void);
+
 /*
  * Finish preparing state data and writing it to WAL.
  */
@@ -1167,6 +1177,37 @@ EndPrepare(GlobalTransaction gxact)
 				(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
 				 errmsg("two-phase state file maximum length exceeded")));
 
+	Assert(gxact->prepare_2pc_mem_data == NULL);
+	Assert(gxact->prepare_2pc_proc == 0);
+
+	if (IsLogicalWorker())
+	{
+		size_t			len = 0;
+		size_t			offset = 0;
+
+		for (record = records.head; record != NULL; record = record->next)
+			len += record->len;
+
+		if (len > 0)
+		{
+			MemoryContext	oldmemctx;
+
+			oldmemctx = MemoryContextSwitchTo(TopMemoryContext);
+
+			gxact->prepare_2pc_mem_data = palloc(len);
+			gxact->prepare_2pc_mem_len = len;
+			gxact->prepare_2pc_proc = getpid();
+
+			for (record = records.head; record != NULL; record = record->next)
+			{
+				memcpy((char *)gxact->prepare_2pc_mem_data + offset, record->data, record->len);
+				offset += record->len;
+			}
+
+			MemoryContextSwitchTo(oldmemctx);
+		}
+	}
+
 	/*
 	 * Now writing 2PC state data to WAL. We let the WAL's CRC protection
 	 * cover us, so no need to calculate a separate CRC.
@@ -1202,8 +1243,24 @@ EndPrepare(GlobalTransaction gxact)
 								   gxact->prepare_end_lsn);
 	}
 
+#if !defined(POSTGRESQL_TWOPHASE_SUPPORT_ASYNC_COMMIT)
+
 	XLogFlush(gxact->prepare_end_lsn);
 
+#else
+
+	if (synchronous_commit > SYNCHRONOUS_COMMIT_OFF)
+	{
+		/* Flush XLOG to disk */
+		XLogFlush(gxact->prepare_end_lsn);
+	}
+	else
+	{
+		XLogSetAsyncXactLSN(gxact->prepare_end_lsn);
+	}
+
+#endif
+
 	/* If we crash now, we have prepared: WAL replay will fix things */
 
 	/* Store record's start location to read that later on Commit */
@@ -1495,6 +1552,7 @@ FinishPreparedTransaction(const char *gid, bool isCommit)
 	xl_xact_stats_item *commitstats;
 	xl_xact_stats_item *abortstats;
 	SharedInvalidationMessage *invalmsgs;
+	bool		is_local_2pc_buf = false;
 
 	/*
 	 * Validate the GID, and lock the GXACT to ensure that two backends do not
@@ -1509,12 +1567,19 @@ FinishPreparedTransaction(const char *gid, bool isCommit)
 	 * in WAL files if the LSN is after the last checkpoint record, or moved
 	 * to disk if for some reason they have lived for a long time.
 	 */
-	if (gxact->ondisk)
+	if (gxact->prepare_2pc_mem_data != NULL && gxact->prepare_2pc_proc == getpid())
+	{
+		Assert(IsLogicalWorker());
+		Assert(gxact->prepare_2pc_proc == getpid());
+		buf = gxact->prepare_2pc_mem_data;
+		/* ereport(LOG, errmsg("%s:%d", __FUNCTION__, __LINE__)); */
+		is_local_2pc_buf = true;
+	}
+	else if (gxact->ondisk)
 		buf = ReadTwoPhaseFile(xid, false);
 	else
 		XlogReadTwoPhaseData(gxact->prepare_start_lsn, &buf, NULL);
 
-
 	/*
 	 * Disassemble the header area
 	 */
@@ -1638,6 +1703,19 @@ FinishPreparedTransaction(const char *gid, bool isCommit)
 	/* Clear shared memory state */
 	RemoveGXact(gxact);
 
+	if (gxact->prepare_2pc_mem_data != NULL)
+	{
+		MemoryContext		memctx;
+		//Assert(gxact->prepare_2pc_proc == getpid());
+		memctx = MemoryContextSwitchTo(TopMemoryContext);
+		if (gxact->prepare_2pc_proc == getpid())
+			pfree(gxact->prepare_2pc_mem_data);
+		gxact->prepare_2pc_mem_data = NULL;
+		gxact->prepare_2pc_mem_len = 0;
+		gxact->prepare_2pc_proc = 0;
+		MemoryContextSwitchTo(memctx);
+	}
+
 	/*
 	 * Release the lock as all callbacks are called and shared memory cleanup
 	 * is done.
@@ -1657,7 +1735,8 @@ FinishPreparedTransaction(const char *gid, bool isCommit)
 
 	RESUME_INTERRUPTS();
 
-	pfree(buf);
+	if (!is_local_2pc_buf)
+		pfree(buf);
 }
 
 /*
@@ -2349,12 +2428,38 @@ RecordTransactionCommitPrepared(TransactionId xid,
 	 * a contradiction)
 	 */
 
+#if !defined(POSTGRESQL_TWOPHASE_SUPPORT_ASYNC_COMMIT)
+
 	/* Flush XLOG to disk */
 	XLogFlush(recptr);
 
 	/* Mark the transaction committed in pg_xact */
 	TransactionIdCommitTree(xid, nchildren, children);
 
+#else
+
+	if (synchronous_commit > SYNCHRONOUS_COMMIT_OFF)
+	{
+		/* Flush XLOG to disk */
+		XLogFlush(recptr);
+
+		/* Mark the transaction committed in pg_xact */
+		TransactionIdCommitTree(xid, nchildren, children);
+	}
+	else
+	{
+		XLogSetAsyncXactLSN(recptr);
+
+		/*
+		 * We must not immediately update the CLOG, since we didn't flush the
+		 * XLOG. Instead, we store the LSN up to which the XLOG must be
+		 * flushed before the CLOG may be updated.
+		 */
+		TransactionIdAsyncCommitTree(xid, nchildren, children, recptr);
+	}
+
+#endif
+
 	/* Checkpoint can proceed now */
 	MyProc->delayChkptFlags &= ~DELAY_CHKPT_START;
 
-- 
2.34.1

From cbaaa7270d771f9ccd6def08f0f02ce61dc15ff6 Mon Sep 17 00:00:00 2001
From: Vitaly Davydov <v.davydov@postgrespro.ru>
Date: Thu, 29 Feb 2024 18:58:13 +0300
Subject: [PATCH] Async commit support for twophase transactions

---
 src/backend/access/transam/twophase.c | 171 +++++++++++++++++++++-----
 1 file changed, 138 insertions(+), 33 deletions(-)

diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index 234c8d08eb..352266be14 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -109,6 +109,8 @@
 #include "utils/memutils.h"
 #include "utils/timestamp.h"
 
+#define POSTGRESQL_TWOPHASE_SUPPORT_ASYNC_COMMIT
+
 /*
  * Directory where Two-phase commit files reside within PGDATA
  */
@@ -169,6 +171,7 @@ typedef struct GlobalTransactionData
 	BackendId	locking_backend;	/* backend currently working on the xact */
 	bool		valid;			/* true if PGPROC entry is in proc array */
 	bool		ondisk;			/* true if prepare state file is on disk */
+	bool		infile;			/* true if prepared state saved in file (but not fsync-ed) */
 	bool		inredo;			/* true if entry was added via xlog_redo */
 	char		gid[GIDSIZE];	/* The GID assigned to the prepared xact */
 }			GlobalTransactionData;
@@ -227,12 +230,14 @@ static void RemoveGXact(GlobalTransaction gxact);
 static void XlogReadTwoPhaseData(XLogRecPtr lsn, char **buf, int *len);
 static char *ProcessTwoPhaseBuffer(TransactionId xid,
 								   XLogRecPtr prepare_start_lsn,
-								   bool fromdisk, bool setParent, bool setNextXid);
+								   bool fromdisk, bool setParent, bool setNextXid,
+								   const char *filename);
 static void MarkAsPreparingGuts(GlobalTransaction gxact, TransactionId xid,
 								const char *gid, TimestampTz prepared_at, Oid owner,
 								Oid databaseid);
 static void RemoveTwoPhaseFile(TransactionId xid, bool giveWarning);
-static void RecreateTwoPhaseFile(TransactionId xid, void *content, int len);
+static void RemoveTwoPhaseFileByName(const char *filename, bool giveWarning);
+static void RecreateTwoPhaseFile(TransactionId xid, void *content, int len, bool dosync);
 
 /*
  * Initialization of shared memory
@@ -427,6 +432,7 @@ MarkAsPreparing(TransactionId xid, const char *gid,
 
 	MarkAsPreparingGuts(gxact, xid, gid, prepared_at, owner, databaseid);
 
+	gxact->infile = false;
 	gxact->ondisk = false;
 
 	/* And insert it into the active array */
@@ -1204,6 +1210,37 @@ EndPrepare(GlobalTransaction gxact)
 				(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
 				 errmsg("two-phase state file maximum length exceeded")));
 
+#ifdef POSTGRESQL_TWOPHASE_SUPPORT_ASYNC_COMMIT
+
+	Assert(gxact->infile == false);
+
+	if (synchronous_commit == SYNCHRONOUS_COMMIT_OFF)
+	{
+		char		   *buf;
+		size_t			len = 0;
+		size_t			offset = 0;
+
+		for (record = records.head; record != NULL; record = record->next)
+			len += record->len;
+
+		if (len > 0)
+		{
+			buf = palloc(len);
+
+			for (record = records.head; record != NULL; record = record->next)
+			{
+				memcpy(buf + offset, record->data, record->len);
+				offset += record->len;
+			}
+
+			RecreateTwoPhaseFile(gxact->xid, buf, len, false);
+			pfree(buf);
+			gxact->infile = true;
+		}
+	}
+
+#endif
+
 	/*
 	 * Now writing 2PC state data to WAL. We let the WAL's CRC protection
 	 * cover us, so no need to calculate a separate CRC.
@@ -1239,8 +1276,24 @@ EndPrepare(GlobalTransaction gxact)
 								   gxact->prepare_end_lsn);
 	}
 
+#if !defined(POSTGRESQL_TWOPHASE_SUPPORT_ASYNC_COMMIT)
+
 	XLogFlush(gxact->prepare_end_lsn);
 
+#else
+
+	if (synchronous_commit > SYNCHRONOUS_COMMIT_OFF)
+	{
+		/* Flush XLOG to disk */
+		XLogFlush(gxact->prepare_end_lsn);
+	}
+	else
+	{
+		XLogSetAsyncXactLSN(gxact->prepare_end_lsn);
+	}
+
+#endif
+
 	/* If we crash now, we have prepared: WAL replay will fix things */
 
 	/* Store record's start location to read that later on Commit */
@@ -1546,12 +1599,11 @@ FinishPreparedTransaction(const char *gid, bool isCommit)
 	 * in WAL files if the LSN is after the last checkpoint record, or moved
 	 * to disk if for some reason they have lived for a long time.
 	 */
-	if (gxact->ondisk)
+	if (gxact->infile || gxact->ondisk)
 		buf = ReadTwoPhaseFile(xid, false);
 	else
 		XlogReadTwoPhaseData(gxact->prepare_start_lsn, &buf, NULL);
 
-
 	/*
 	 * Disassemble the header area
 	 */
@@ -1687,7 +1739,7 @@ FinishPreparedTransaction(const char *gid, bool isCommit)
 	/*
 	 * And now we can clean up any files we may have left.
 	 */
-	if (gxact->ondisk)
+	if (gxact->infile || gxact->ondisk)
 		RemoveTwoPhaseFile(xid, true);
 
 	MyLockedGxact = NULL;
@@ -1741,6 +1793,20 @@ RemoveTwoPhaseFile(TransactionId xid, bool giveWarning)
 					 errmsg("could not remove file \"%s\": %m", path)));
 }
 
+static void
+RemoveTwoPhaseFileByName(const char *filename, bool giveWarning)
+{
+	char		path[MAXPGPATH];
+
+	snprintf(path, MAXPGPATH, TWOPHASE_DIR "/%s", filename);
+
+	if (unlink(path))
+		if (errno != ENOENT || giveWarning)
+			ereport(WARNING,
+					(errcode_for_file_access(),
+					 errmsg("could not remove file \"%s\": %m", path)));
+}
+
 /*
  * Recreates a state file. This is used in WAL replay and during
  * checkpoint creation.
@@ -1748,7 +1814,7 @@ RemoveTwoPhaseFile(TransactionId xid, bool giveWarning)
  * Note: content and len don't include CRC.
  */
 static void
-RecreateTwoPhaseFile(TransactionId xid, void *content, int len)
+RecreateTwoPhaseFile(TransactionId xid, void *content, int len, bool dosync)
 {
 	char		path[MAXPGPATH];
 	pg_crc32c	statefile_crc;
@@ -1791,16 +1857,19 @@ RecreateTwoPhaseFile(TransactionId xid, void *content, int len)
 	}
 	pgstat_report_wait_end();
 
-	/*
-	 * We must fsync the file because the end-of-replay checkpoint will not do
-	 * so, there being no GXACT in shared memory yet to tell it to.
-	 */
-	pgstat_report_wait_start(WAIT_EVENT_TWOPHASE_FILE_SYNC);
-	if (pg_fsync(fd) != 0)
-		ereport(ERROR,
-				(errcode_for_file_access(),
-				 errmsg("could not fsync file \"%s\": %m", path)));
-	pgstat_report_wait_end();
+	if (dosync)
+	{
+		/*
+		* We must fsync the file because the end-of-replay checkpoint will not do
+		* so, there being no GXACT in shared memory yet to tell it to.
+		*/
+		pgstat_report_wait_start(WAIT_EVENT_TWOPHASE_FILE_SYNC);
+		if (pg_fsync(fd) != 0)
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					errmsg("could not fsync file \"%s\": %m", path)));
+		pgstat_report_wait_end();
+	}
 
 	if (CloseTransientFile(fd) != 0)
 		ereport(ERROR,
@@ -1871,7 +1940,8 @@ CheckPointTwoPhase(XLogRecPtr redo_horizon)
 			int			len;
 
 			XlogReadTwoPhaseData(gxact->prepare_start_lsn, &buf, &len);
-			RecreateTwoPhaseFile(gxact->xid, buf, len);
+			RecreateTwoPhaseFile(gxact->xid, buf, len, true);
+			gxact->infile = true;
 			gxact->ondisk = true;
 			gxact->prepare_start_lsn = InvalidXLogRecPtr;
 			gxact->prepare_end_lsn = InvalidXLogRecPtr;
@@ -1930,7 +2000,8 @@ restoreTwoPhaseData(void)
 			xid = XidFromFullTransactionId(fxid);
 
 			buf = ProcessTwoPhaseBuffer(xid, InvalidXLogRecPtr,
-										true, false, false);
+										true, false, false,
+										clde->d_name);
 			if (buf == NULL)
 				continue;
 
@@ -1997,7 +2068,8 @@ PrescanPreparedTransactions(TransactionId **xids_p, int *nxids_p)
 
 		buf = ProcessTwoPhaseBuffer(xid,
 									gxact->prepare_start_lsn,
-									gxact->ondisk, false, true);
+									gxact->ondisk, false, true,
+									NULL);
 
 		if (buf == NULL)
 			continue;
@@ -2072,7 +2144,8 @@ StandbyRecoverPreparedTransactions(void)
 
 		buf = ProcessTwoPhaseBuffer(xid,
 									gxact->prepare_start_lsn,
-									gxact->ondisk, false, false);
+									gxact->ondisk, false, false,
+									NULL);
 		if (buf != NULL)
 			pfree(buf);
 	}
@@ -2124,7 +2197,8 @@ RecoverPreparedTransactions(void)
 		 */
 		buf = ProcessTwoPhaseBuffer(xid,
 									gxact->prepare_start_lsn,
-									gxact->ondisk, true, false);
+									gxact->ondisk, true, false,
+									NULL);
 		if (buf == NULL)
 			continue;
 
@@ -2202,7 +2276,8 @@ static char *
 ProcessTwoPhaseBuffer(TransactionId xid,
 					  XLogRecPtr prepare_start_lsn,
 					  bool fromdisk,
-					  bool setParent, bool setNextXid)
+					  bool setParent, bool setNextXid,
+					  const char *filename)
 {
 	FullTransactionId nextXid = TransamVariables->nextXid;
 	TransactionId origNextXid = XidFromFullTransactionId(nextXid);
@@ -2216,40 +2291,43 @@ ProcessTwoPhaseBuffer(TransactionId xid,
 	if (!fromdisk)
 		Assert(prepare_start_lsn != InvalidXLogRecPtr);
 
-	/* Already processed? */
-	if (TransactionIdDidCommit(xid) || TransactionIdDidAbort(xid))
+	/* Reject XID if too new */
+	if (TransactionIdFollowsOrEquals(xid, origNextXid))
 	{
 		if (fromdisk)
 		{
 			ereport(WARNING,
-					(errmsg("removing stale two-phase state file for transaction %u",
+					(errmsg("removing future two-phase state file for transaction %u",
 							xid)));
-			RemoveTwoPhaseFile(xid, true);
+			if (filename)
+				RemoveTwoPhaseFileByName(filename, true);
+			else
+				RemoveTwoPhaseFile(xid, true);
 		}
 		else
 		{
 			ereport(WARNING,
-					(errmsg("removing stale two-phase state from memory for transaction %u",
+					(errmsg("removing future two-phase state from memory for transaction %u",
 							xid)));
 			PrepareRedoRemove(xid, true);
 		}
 		return NULL;
 	}
 
-	/* Reject XID if too new */
-	if (TransactionIdFollowsOrEquals(xid, origNextXid))
+	/* Already processed? */
+	if (TransactionIdDidCommit(xid) || TransactionIdDidAbort(xid))
 	{
 		if (fromdisk)
 		{
 			ereport(WARNING,
-					(errmsg("removing future two-phase state file for transaction %u",
+					(errmsg("removing stale two-phase state file for transaction %u",
 							xid)));
 			RemoveTwoPhaseFile(xid, true);
 		}
 		else
 		{
 			ereport(WARNING,
-					(errmsg("removing future two-phase state from memory for transaction %u",
+					(errmsg("removing stale two-phase state from memory for transaction %u",
 							xid)));
 			PrepareRedoRemove(xid, true);
 		}
@@ -2388,12 +2466,38 @@ RecordTransactionCommitPrepared(TransactionId xid,
 	 * a contradiction)
 	 */
 
+#if !defined(POSTGRESQL_TWOPHASE_SUPPORT_ASYNC_COMMIT)
+
 	/* Flush XLOG to disk */
 	XLogFlush(recptr);
 
 	/* Mark the transaction committed in pg_xact */
 	TransactionIdCommitTree(xid, nchildren, children);
 
+#else
+
+	if (synchronous_commit > SYNCHRONOUS_COMMIT_OFF)
+	{
+		/* Flush XLOG to disk */
+		XLogFlush(recptr);
+
+		/* Mark the transaction committed in pg_xact */
+		TransactionIdCommitTree(xid, nchildren, children);
+	}
+	else
+	{
+		XLogSetAsyncXactLSN(recptr);
+
+		/*
+		 * We must not immediately update the CLOG, since we didn't flush the
+		 * XLOG. Instead, we store the LSN up to which the XLOG must be
+		 * flushed before the CLOG may be updated.
+		 */
+		TransactionIdAsyncCommitTree(xid, nchildren, children, recptr);
+	}
+
+#endif
+
 	/* Checkpoint can proceed now */
 	MyProc->delayChkptFlags &= ~DELAY_CHKPT_START;
 
@@ -2567,6 +2671,7 @@ PrepareRedoAdd(char *buf, XLogRecPtr start_lsn,
 	gxact->locking_backend = InvalidBackendId;
 	gxact->valid = false;
 	gxact->ondisk = XLogRecPtrIsInvalid(start_lsn);
+	gxact->infile = gxact->ondisk;
 	gxact->inredo = true;		/* yes, added in redo */
 	strcpy(gxact->gid, gid);
 
@@ -2625,7 +2730,7 @@ PrepareRedoRemove(TransactionId xid, bool giveWarning)
 	 * And now we can clean up any files we may have left.
 	 */
 	elog(DEBUG2, "removing 2PC data for transaction %u", xid);
-	if (gxact->ondisk)
+	if (gxact->infile || gxact->ondisk)
 		RemoveTwoPhaseFile(xid, giveWarning);
 	RemoveGXact(gxact);
 }
@@ -2673,7 +2778,7 @@ LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 			 * do this optimization if we encounter many collisions in GID
 			 * between publisher and subscriber.
 			 */
-			if (gxact->ondisk)
+			if (gxact->infile || gxact->ondisk)
 				buf = ReadTwoPhaseFile(gxact->xid, false);
 			else
 			{
-- 
2.34.1

From bb19db9bd4e73d8892f202fb7b8771c25a033681 Mon Sep 17 00:00:00 2001
From: Ajin Cherian <ajinc@fast.au.fujitsu.com>
Date: Thu, 4 Apr 2024 01:17:29 -0400
Subject: [PATCH v1] Allow altering of two_phase option in subscribers

This patch allows user to alter two_phase option on a subscriber provided no uncommitted
prepared transactions are pending on that subscription.
---
 src/backend/access/transam/twophase.c      | 42 ++++++++++++++++++++++++++++++
 src/backend/commands/subscriptioncmds.c    | 35 ++++++++++++++++++++++---
 src/backend/replication/logical/launcher.c | 22 +++++++++++++---
 src/backend/replication/logical/worker.c   |  3 ---
 src/include/access/twophase.h              |  3 +++
 src/include/replication/logicallauncher.h  |  2 +-
 6 files changed, 96 insertions(+), 11 deletions(-)

diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index 8090ac9..b0aae25 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -2682,3 +2682,45 @@ LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 	LWLockRelease(TwoPhaseStateLock);
 	return found;
 }
+
+/*
+ * checkGid
+ */
+static bool
+checkGid(char *gid, Oid subid)
+{
+	int ret;
+	Oid subid_written, xid;
+
+	ret = sscanf(gid, "pg_gid_%u_%u", &subid_written, &xid);
+
+	if (ret != 2 || subid != subid_written)
+		return false;
+
+	return true;
+}
+
+/*
+ * LookupGXactBySubid
+ *		Check if the prepared transaction done by apply worker exists.
+ */
+bool
+LookupGXactBySubid(Oid subid)
+{
+	bool		found = false;
+
+	LWLockAcquire(TwoPhaseStateLock, LW_SHARED);
+	for (int i = 0; i < TwoPhaseState->numPrepXacts; i++)
+	{
+		GlobalTransaction gxact = TwoPhaseState->prepXacts[i];
+
+		/* Ignore not-yet-valid GIDs. */
+		if (gxact->valid &&	checkGid(gxact->gid, subid))
+		{
+			found = true;
+			break;
+		}
+	}
+	LWLockRelease(TwoPhaseStateLock);
+	return found;
+}
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index 5a47fa9..8306929 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -16,6 +16,7 @@
 
 #include "access/htup_details.h"
 #include "access/table.h"
+#include "access/twophase.h"
 #include "access/xact.h"
 #include "catalog/catalog.h"
 #include "catalog/dependency.h"
@@ -868,7 +869,7 @@ CreateSubscription(ParseState *pstate, CreateSubscriptionStmt *stmt,
 	pgstat_create_subscription(subid);
 
 	if (opts.enabled)
-		ApplyLauncherWakeupAtCommit();
+		ApplyLauncherWakeupAtEOXact(true);
 
 	ObjectAddressSet(myself, SubscriptionRelationId, subid);
 
@@ -1165,7 +1166,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 			{
 				supported_opts = (SUBOPT_SLOT_NAME |
 								  SUBOPT_SYNCHRONOUS_COMMIT | SUBOPT_BINARY |
-								  SUBOPT_STREAMING | SUBOPT_DISABLE_ON_ERR |
+								  SUBOPT_STREAMING | SUBOPT_TWOPHASE_COMMIT |
+								  SUBOPT_DISABLE_ON_ERR |
 								  SUBOPT_PASSWORD_REQUIRED |
 								  SUBOPT_RUN_AS_OWNER | SUBOPT_FAILOVER |
 								  SUBOPT_ORIGIN);
@@ -1173,6 +1175,31 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 				parse_subscription_options(pstate, stmt->options,
 										   supported_opts, &opts);
 
+				/* XXX */
+				if (IsSet(opts.specified_opts, SUBOPT_TWOPHASE_COMMIT))
+				{
+					/* Stop corresponding worker */
+					logicalrep_worker_stop(subid, InvalidOid);
+
+					/* Request to start worker at the end of transaction */
+					ApplyLauncherWakeupAtEOXact(false);
+
+					/* Check whether the number of prepared transactions */
+					if (!opts.twophase &&
+						form->subtwophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
+						LookupGXactBySubid(subid))
+						ereport(ERROR,
+								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+								 errmsg("cannot disable two_phase when uncommitted prepared transactions present")));
+
+					/* Change system catalog acoordingly */
+					values[Anum_pg_subscription_subtwophasestate - 1] =
+						CharGetDatum(opts.twophase ?
+									 LOGICALREP_TWOPHASE_STATE_PENDING :
+									 LOGICALREP_TWOPHASE_STATE_DISABLED);
+					replaces[Anum_pg_subscription_subtwophasestate - 1] = true;
+				}
+
 				if (IsSet(opts.specified_opts, SUBOPT_SLOT_NAME))
 				{
 					/*
@@ -1299,7 +1326,7 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 				replaces[Anum_pg_subscription_subenabled - 1] = true;
 
 				if (opts.enabled)
-					ApplyLauncherWakeupAtCommit();
+					ApplyLauncherWakeupAtEOXact(true);
 
 				update_tuple = true;
 				break;
@@ -1962,7 +1989,7 @@ AlterSubscriptionOwner_internal(Relation rel, HeapTuple tup, Oid newOwnerId)
 							  form->oid, 0);
 
 	/* Wake up related background processes to handle this change quickly. */
-	ApplyLauncherWakeupAtCommit();
+	ApplyLauncherWakeupAtEOXact(true);
 	LogicalRepWorkersWakeupAtCommit(form->oid);
 }
 
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 66070e9..899ec22 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -89,6 +89,7 @@ static dsa_area *last_start_times_dsa = NULL;
 static dshash_table *last_start_times = NULL;
 
 static bool on_commit_launcher_wakeup = false;
+static bool launcher_wakeup = false;
 
 
 static void ApplyLauncherWakeup(void);
@@ -1085,13 +1086,22 @@ ApplyLauncherForgetWorkerStartTime(Oid subid)
 void
 AtEOXact_ApplyLauncher(bool isCommit)
 {
+	bool kicked = false;
+
 	if (isCommit)
 	{
 		if (on_commit_launcher_wakeup)
+		{
 			ApplyLauncherWakeup();
+			kicked = true;
+		}
 	}
 
+	if (!kicked && launcher_wakeup)
+		ApplyLauncherWakeup();
+
 	on_commit_launcher_wakeup = false;
+	launcher_wakeup = false;
 }
 
 /*
@@ -1102,10 +1112,16 @@ AtEOXact_ApplyLauncher(bool isCommit)
  * tuple was added to the pg_subscription catalog.
 */
 void
-ApplyLauncherWakeupAtCommit(void)
+ApplyLauncherWakeupAtEOXact(bool on_commit)
 {
-	if (!on_commit_launcher_wakeup)
-		on_commit_launcher_wakeup = true;
+	if (on_commit)
+	{
+		if (!on_commit_launcher_wakeup)
+			on_commit_launcher_wakeup = true;
+	}
+	else
+		if (!launcher_wakeup)
+			launcher_wakeup = true;
 }
 
 static void
diff --git a/src/backend/replication/logical/worker.c b/src/backend/replication/logical/worker.c
index b5a80fe..ca3d260 100644
--- a/src/backend/replication/logical/worker.c
+++ b/src/backend/replication/logical/worker.c
@@ -3911,9 +3911,6 @@ maybe_reread_subscription(void)
 	/* !slotname should never happen when enabled is true. */
 	Assert(newsub->slotname);
 
-	/* two-phase should not be altered */
-	Assert(newsub->twophasestate == MySubscription->twophasestate);
-
 	/*
 	 * Exit if any parameter that affects the remote connection was changed.
 	 * The launcher will start a new worker but note that the parallel apply
diff --git a/src/include/access/twophase.h b/src/include/access/twophase.h
index 56248c0..d493ed2 100644
--- a/src/include/access/twophase.h
+++ b/src/include/access/twophase.h
@@ -62,4 +62,7 @@ extern void PrepareRedoRemove(TransactionId xid, bool giveWarning);
 extern void restoreTwoPhaseData(void);
 extern bool LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 						TimestampTz origin_prepare_timestamp);
+
+extern bool LookupGXactBySubid(Oid subid);
+
 #endif							/* TWOPHASE_H */
diff --git a/src/include/replication/logicallauncher.h b/src/include/replication/logicallauncher.h
index ff0438b..075842c 100644
--- a/src/include/replication/logicallauncher.h
+++ b/src/include/replication/logicallauncher.h
@@ -24,7 +24,7 @@ extern void ApplyLauncherShmemInit(void);
 
 extern void ApplyLauncherForgetWorkerStartTime(Oid subid);
 
-extern void ApplyLauncherWakeupAtCommit(void);
+extern void ApplyLauncherWakeupAtEOXact(bool on_commit);
 extern void AtEOXact_ApplyLauncher(bool isCommit);
 
 extern bool IsLogicalLauncher(void);
-- 
1.8.3.1

From 10604538a61c4b015378b5e33af49405ec774366 Mon Sep 17 00:00:00 2001
From: Ajin Cherian <ajinc@fast.au.fujitsu.com>
Date: Fri, 5 Apr 2024 06:47:18 -0400
Subject: [PATCH v2] Allow altering of two_phase option of a SUBSCRIPTION

This patch allows user to alter two_phase option of a subscriber provided no uncommitted
prepared transactions are pending on that subscription.
---
 src/backend/access/transam/twophase.c              | 42 ++++++++++++++++++++++
 src/backend/commands/subscriptioncmds.c            | 42 ++++++++++++++++++----
 .../libpqwalreceiver/libpqwalreceiver.c            |  7 ++--
 src/backend/replication/logical/launcher.c         | 22 ++++++++++--
 src/backend/replication/logical/worker.c           |  3 --
 src/backend/replication/slot.c                     | 19 +++++++++-
 src/backend/replication/walsender.c                | 20 ++++++++---
 src/include/access/twophase.h                      |  3 ++
 src/include/replication/logicallauncher.h          |  2 +-
 src/include/replication/slot.h                     |  3 +-
 src/include/replication/walreceiver.h              |  5 +--
 11 files changed, 143 insertions(+), 25 deletions(-)

diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index 8090ac9..b0aae25 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -2682,3 +2682,45 @@ LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 	LWLockRelease(TwoPhaseStateLock);
 	return found;
 }
+
+/*
+ * checkGid
+ */
+static bool
+checkGid(char *gid, Oid subid)
+{
+	int ret;
+	Oid subid_written, xid;
+
+	ret = sscanf(gid, "pg_gid_%u_%u", &subid_written, &xid);
+
+	if (ret != 2 || subid != subid_written)
+		return false;
+
+	return true;
+}
+
+/*
+ * LookupGXactBySubid
+ *		Check if the prepared transaction done by apply worker exists.
+ */
+bool
+LookupGXactBySubid(Oid subid)
+{
+	bool		found = false;
+
+	LWLockAcquire(TwoPhaseStateLock, LW_SHARED);
+	for (int i = 0; i < TwoPhaseState->numPrepXacts; i++)
+	{
+		GlobalTransaction gxact = TwoPhaseState->prepXacts[i];
+
+		/* Ignore not-yet-valid GIDs. */
+		if (gxact->valid &&	checkGid(gxact->gid, subid))
+		{
+			found = true;
+			break;
+		}
+	}
+	LWLockRelease(TwoPhaseStateLock);
+	return found;
+}
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index 5a47fa9..6643fc0 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -16,6 +16,7 @@
 
 #include "access/htup_details.h"
 #include "access/table.h"
+#include "access/twophase.h"
 #include "access/xact.h"
 #include "catalog/catalog.h"
 #include "catalog/dependency.h"
@@ -849,7 +850,7 @@ CreateSubscription(ParseState *pstate, CreateSubscriptionStmt *stmt,
 			else if (opts.slot_name &&
 					 (opts.failover || walrcv_server_version(wrconn) >= 170000))
 			{
-				walrcv_alter_slot(wrconn, opts.slot_name, opts.failover);
+				walrcv_alter_slot(wrconn, opts.slot_name, opts.twophase, opts.failover);
 			}
 		}
 		PG_FINALLY();
@@ -868,7 +869,7 @@ CreateSubscription(ParseState *pstate, CreateSubscriptionStmt *stmt,
 	pgstat_create_subscription(subid);
 
 	if (opts.enabled)
-		ApplyLauncherWakeupAtCommit();
+		ApplyLauncherWakeupAtEOXact(true);
 
 	ObjectAddressSet(myself, SubscriptionRelationId, subid);
 
@@ -1165,7 +1166,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 			{
 				supported_opts = (SUBOPT_SLOT_NAME |
 								  SUBOPT_SYNCHRONOUS_COMMIT | SUBOPT_BINARY |
-								  SUBOPT_STREAMING | SUBOPT_DISABLE_ON_ERR |
+								  SUBOPT_STREAMING | SUBOPT_TWOPHASE_COMMIT |
+								  SUBOPT_DISABLE_ON_ERR |
 								  SUBOPT_PASSWORD_REQUIRED |
 								  SUBOPT_RUN_AS_OWNER | SUBOPT_FAILOVER |
 								  SUBOPT_ORIGIN);
@@ -1173,6 +1175,31 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 				parse_subscription_options(pstate, stmt->options,
 										   supported_opts, &opts);
 
+				/* XXX */
+				if (IsSet(opts.specified_opts, SUBOPT_TWOPHASE_COMMIT))
+				{
+					/* Stop corresponding worker */
+					logicalrep_worker_stop(subid, InvalidOid);
+
+					/* Request to start worker at the end of transaction */
+					ApplyLauncherWakeupAtEOXact(false);
+
+					/* Check whether the number of prepared transactions */
+					if (!opts.twophase &&
+						form->subtwophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
+						LookupGXactBySubid(subid))
+						ereport(ERROR,
+								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+								 errmsg("cannot disable two_phase when uncommitted prepared transactions present")));
+
+					/* Change system catalog acoordingly */
+					values[Anum_pg_subscription_subtwophasestate - 1] =
+						CharGetDatum(opts.twophase ?
+									 LOGICALREP_TWOPHASE_STATE_PENDING :
+									 LOGICALREP_TWOPHASE_STATE_DISABLED);
+					replaces[Anum_pg_subscription_subtwophasestate - 1] = true;
+				}
+
 				if (IsSet(opts.specified_opts, SUBOPT_SLOT_NAME))
 				{
 					/*
@@ -1299,7 +1326,7 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 				replaces[Anum_pg_subscription_subenabled - 1] = true;
 
 				if (opts.enabled)
-					ApplyLauncherWakeupAtCommit();
+					ApplyLauncherWakeupAtEOXact(true);
 
 				update_tuple = true;
 				break;
@@ -1521,7 +1548,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 	 * doing the database operations we won't be able to rollback altered
 	 * slot.
 	 */
-	if (replaces[Anum_pg_subscription_subfailover - 1])
+	if (replaces[Anum_pg_subscription_subtwophasestate - 1] ||
+		replaces[Anum_pg_subscription_subfailover - 1])
 	{
 		bool		must_use_password;
 		char	   *err;
@@ -1541,7 +1569,7 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 
 		PG_TRY();
 		{
-			walrcv_alter_slot(wrconn, sub->slotname, opts.failover);
+			walrcv_alter_slot(wrconn, sub->slotname, opts.twophase, opts.failover);
 		}
 		PG_FINALLY();
 		{
@@ -1962,7 +1990,7 @@ AlterSubscriptionOwner_internal(Relation rel, HeapTuple tup, Oid newOwnerId)
 							  form->oid, 0);
 
 	/* Wake up related background processes to handle this change quickly. */
-	ApplyLauncherWakeupAtCommit();
+	ApplyLauncherWakeupAtEOXact(true);
 	LogicalRepWorkersWakeupAtCommit(form->oid);
 }
 
diff --git a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
index 761bf0f..9f7a936 100644
--- a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
+++ b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
@@ -80,7 +80,7 @@ static char *libpqrcv_create_slot(WalReceiverConn *conn,
 								  CRSSnapshotAction snapshot_action,
 								  XLogRecPtr *lsn);
 static void libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-								bool failover);
+								bool two_phase, bool failover);
 static pid_t libpqrcv_get_backend_pid(WalReceiverConn *conn);
 static WalRcvExecResult *libpqrcv_exec(WalReceiverConn *conn,
 									   const char *query,
@@ -1121,14 +1121,15 @@ libpqrcv_create_slot(WalReceiverConn *conn, const char *slotname,
  */
 static void
 libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-					bool failover)
+					bool two_phase, bool failover)
 {
 	StringInfoData cmd;
 	PGresult   *res;
 
 	initStringInfo(&cmd);
-	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( FAILOVER %s )",
+	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( TWO_PHASE %s, FAILOVER %s )",
 					 quote_identifier(slotname),
+					 two_phase ? "true" : "false",
 					 failover ? "true" : "false");
 
 	res = libpqrcv_PQexec(conn->streamConn, cmd.data);
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 66070e9..899ec22 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -89,6 +89,7 @@ static dsa_area *last_start_times_dsa = NULL;
 static dshash_table *last_start_times = NULL;
 
 static bool on_commit_launcher_wakeup = false;
+static bool launcher_wakeup = false;
 
 
 static void ApplyLauncherWakeup(void);
@@ -1085,13 +1086,22 @@ ApplyLauncherForgetWorkerStartTime(Oid subid)
 void
 AtEOXact_ApplyLauncher(bool isCommit)
 {
+	bool kicked = false;
+
 	if (isCommit)
 	{
 		if (on_commit_launcher_wakeup)
+		{
 			ApplyLauncherWakeup();
+			kicked = true;
+		}
 	}
 
+	if (!kicked && launcher_wakeup)
+		ApplyLauncherWakeup();
+
 	on_commit_launcher_wakeup = false;
+	launcher_wakeup = false;
 }
 
 /*
@@ -1102,10 +1112,16 @@ AtEOXact_ApplyLauncher(bool isCommit)
  * tuple was added to the pg_subscription catalog.
 */
 void
-ApplyLauncherWakeupAtCommit(void)
+ApplyLauncherWakeupAtEOXact(bool on_commit)
 {
-	if (!on_commit_launcher_wakeup)
-		on_commit_launcher_wakeup = true;
+	if (on_commit)
+	{
+		if (!on_commit_launcher_wakeup)
+			on_commit_launcher_wakeup = true;
+	}
+	else
+		if (!launcher_wakeup)
+			launcher_wakeup = true;
 }
 
 static void
diff --git a/src/backend/replication/logical/worker.c b/src/backend/replication/logical/worker.c
index b5a80fe..ca3d260 100644
--- a/src/backend/replication/logical/worker.c
+++ b/src/backend/replication/logical/worker.c
@@ -3911,9 +3911,6 @@ maybe_reread_subscription(void)
 	/* !slotname should never happen when enabled is true. */
 	Assert(newsub->slotname);
 
-	/* two-phase should not be altered */
-	Assert(newsub->twophasestate == MySubscription->twophasestate);
-
 	/*
 	 * Exit if any parameter that affects the remote connection was changed.
 	 * The launcher will start a new worker but note that the parallel apply
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 3bddaae..3d24ebb 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -800,8 +800,10 @@ ReplicationSlotDrop(const char *name, bool nowait)
  * Change the definition of the slot identified by the specified name.
  */
 void
-ReplicationSlotAlter(const char *name, bool failover)
+ReplicationSlotAlter(const char *name, bool two_phase, bool failover)
 {
+	bool		update_slot = false;
+
 	Assert(MyReplicationSlot == NULL);
 
 	ReplicationSlotAcquire(name, false);
@@ -844,12 +846,27 @@ ReplicationSlotAlter(const char *name, bool failover)
 				errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 				errmsg("cannot enable failover for a temporary replication slot"));
 
+	if (MyReplicationSlot->data.two_phase != two_phase)
+	{
+		SpinLockAcquire(&MyReplicationSlot->mutex);
+		MyReplicationSlot->data.two_phase = two_phase;
+		SpinLockRelease(&MyReplicationSlot->mutex);
+
+		update_slot = true;
+	}
+
+
 	if (MyReplicationSlot->data.failover != failover)
 	{
 		SpinLockAcquire(&MyReplicationSlot->mutex);
 		MyReplicationSlot->data.failover = failover;
 		SpinLockRelease(&MyReplicationSlot->mutex);
 
+		update_slot = true;
+	}
+
+	if (update_slot)
+	{
 		ReplicationSlotMarkDirty();
 		ReplicationSlotSave();
 	}
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index bc40c45..be15506 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1411,14 +1411,25 @@ DropReplicationSlot(DropReplicationSlotCmd *cmd)
  * Process extra options given to ALTER_REPLICATION_SLOT.
  */
 static void
-ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd, bool *failover)
+ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd,
+						  bool *two_phase, bool *failover)
 {
+	bool		two_phase_given = false;
 	bool		failover_given = false;
 
 	/* Parse options */
 	foreach_ptr(DefElem, defel, cmd->options)
 	{
-		if (strcmp(defel->defname, "failover") == 0)
+		if (strcmp(defel->defname, "two_phase") == 0)
+		{
+			if (two_phase_given)
+				ereport(ERROR,
+						(errcode(ERRCODE_SYNTAX_ERROR),
+						 errmsg("conflicting or redundant options")));
+			two_phase_given = true;
+			*two_phase = defGetBoolean(defel);
+		}
+		else if (strcmp(defel->defname, "failover") == 0)
 		{
 			if (failover_given)
 				ereport(ERROR,
@@ -1438,10 +1449,11 @@ ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd, bool *failover)
 static void
 AlterReplicationSlot(AlterReplicationSlotCmd *cmd)
 {
+	bool		two_phase = false;
 	bool		failover = false;
 
-	ParseAlterReplSlotOptions(cmd, &failover);
-	ReplicationSlotAlter(cmd->slotname, failover);
+	ParseAlterReplSlotOptions(cmd, &two_phase, &failover);
+	ReplicationSlotAlter(cmd->slotname, two_phase, failover);
 }
 
 /*
diff --git a/src/include/access/twophase.h b/src/include/access/twophase.h
index 56248c0..d493ed2 100644
--- a/src/include/access/twophase.h
+++ b/src/include/access/twophase.h
@@ -62,4 +62,7 @@ extern void PrepareRedoRemove(TransactionId xid, bool giveWarning);
 extern void restoreTwoPhaseData(void);
 extern bool LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 						TimestampTz origin_prepare_timestamp);
+
+extern bool LookupGXactBySubid(Oid subid);
+
 #endif							/* TWOPHASE_H */
diff --git a/src/include/replication/logicallauncher.h b/src/include/replication/logicallauncher.h
index ff0438b..075842c 100644
--- a/src/include/replication/logicallauncher.h
+++ b/src/include/replication/logicallauncher.h
@@ -24,7 +24,7 @@ extern void ApplyLauncherShmemInit(void);
 
 extern void ApplyLauncherForgetWorkerStartTime(Oid subid);
 
-extern void ApplyLauncherWakeupAtCommit(void);
+extern void ApplyLauncherWakeupAtEOXact(bool on_commit);
 extern void AtEOXact_ApplyLauncher(bool isCommit);
 
 extern bool IsLogicalLauncher(void);
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 7b937d1..2fcb114 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -243,7 +243,8 @@ extern void ReplicationSlotCreate(const char *name, bool db_specific,
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
 extern void ReplicationSlotDropAcquired(void);
-extern void ReplicationSlotAlter(const char *name, bool failover);
+extern void ReplicationSlotAlter(const char *name, bool two_phase,
+								 bool failover);
 
 extern void ReplicationSlotAcquire(const char *name, bool nowait);
 extern void ReplicationSlotRelease(void);
diff --git a/src/include/replication/walreceiver.h b/src/include/replication/walreceiver.h
index 12f71fa..a443f40 100644
--- a/src/include/replication/walreceiver.h
+++ b/src/include/replication/walreceiver.h
@@ -377,6 +377,7 @@ typedef char *(*walrcv_create_slot_fn) (WalReceiverConn *conn,
  */
 typedef void (*walrcv_alter_slot_fn) (WalReceiverConn *conn,
 									  const char *slotname,
+									  bool two_phase,
 									  bool failover);
 
 /*
@@ -455,8 +456,8 @@ extern PGDLLIMPORT WalReceiverFunctionsType *WalReceiverFunctions;
 	WalReceiverFunctions->walrcv_send(conn, buffer, nbytes)
 #define walrcv_create_slot(conn, slotname, temporary, two_phase, failover, snapshot_action, lsn) \
 	WalReceiverFunctions->walrcv_create_slot(conn, slotname, temporary, two_phase, failover, snapshot_action, lsn)
-#define walrcv_alter_slot(conn, slotname, failover) \
-	WalReceiverFunctions->walrcv_alter_slot(conn, slotname, failover)
+#define walrcv_alter_slot(conn, slotname, two_phase, failover) \
+	WalReceiverFunctions->walrcv_alter_slot(conn, slotname, two_phase, failover)
 #define walrcv_get_backend_pid(conn) \
 	WalReceiverFunctions->walrcv_get_backend_pid(conn)
 #define walrcv_exec(conn, exec, nRetTypes, retTypes) \
-- 
1.8.3.1

From d6d4b8ac93c60dcaadb53c6cb9a446ae0882511b Mon Sep 17 00:00:00 2001
From: Ajin Cherian <ajinc@fast.au.fujitsu.com>
Date: Fri, 5 Apr 2024 06:47:18 -0400
Subject: [PATCH v3 1/5] Allow altering of two_phase option of a SUBSCRIPTION

This patch allows user to alter two_phase option of a subscriber provided no uncommitted
prepared transactions are pending on that subscription.

Author: Cherian Ajin, Hayato Kuroda
---
 src/backend/access/transam/twophase.c         | 43 +++++++++++++++++++
 src/backend/commands/subscriptioncmds.c       | 42 +++++++++++++++---
 .../libpqwalreceiver/libpqwalreceiver.c       |  7 +--
 src/backend/replication/logical/launcher.c    | 21 +++++++--
 src/backend/replication/logical/worker.c      |  3 --
 src/backend/replication/slot.c                | 19 +++++++-
 src/backend/replication/walsender.c           | 20 +++++++--
 src/bin/psql/tab-complete.c                   |  2 +-
 src/include/access/twophase.h                 |  3 ++
 src/include/replication/logicallauncher.h     |  2 +-
 src/include/replication/slot.h                |  3 +-
 src/include/replication/walreceiver.h         |  5 ++-
 src/test/regress/expected/subscription.out    |  5 +--
 src/test/regress/sql/subscription.sql         |  5 +--
 14 files changed, 146 insertions(+), 34 deletions(-)

diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index 8090ac9fc1..495f99a357 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -2682,3 +2682,46 @@ LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 	LWLockRelease(TwoPhaseStateLock);
 	return found;
 }
+
+/*
+ * checkGid
+ */
+static bool
+checkGid(char *gid, Oid subid)
+{
+	int			ret;
+	Oid			subid_written,
+				xid;
+
+	ret = sscanf(gid, "pg_gid_%u_%u", &subid_written, &xid);
+
+	if (ret != 2 || subid != subid_written)
+		return false;
+
+	return true;
+}
+
+/*
+ * LookupGXactBySubid
+ *		Check if the prepared transaction done by apply worker exists.
+ */
+bool
+LookupGXactBySubid(Oid subid)
+{
+	bool		found = false;
+
+	LWLockAcquire(TwoPhaseStateLock, LW_SHARED);
+	for (int i = 0; i < TwoPhaseState->numPrepXacts; i++)
+	{
+		GlobalTransaction gxact = TwoPhaseState->prepXacts[i];
+
+		/* Ignore not-yet-valid GIDs. */
+		if (gxact->valid && checkGid(gxact->gid, subid))
+		{
+			found = true;
+			break;
+		}
+	}
+	LWLockRelease(TwoPhaseStateLock);
+	return found;
+}
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index 5a47fa984d..6643fc08a6 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -16,6 +16,7 @@
 
 #include "access/htup_details.h"
 #include "access/table.h"
+#include "access/twophase.h"
 #include "access/xact.h"
 #include "catalog/catalog.h"
 #include "catalog/dependency.h"
@@ -849,7 +850,7 @@ CreateSubscription(ParseState *pstate, CreateSubscriptionStmt *stmt,
 			else if (opts.slot_name &&
 					 (opts.failover || walrcv_server_version(wrconn) >= 170000))
 			{
-				walrcv_alter_slot(wrconn, opts.slot_name, opts.failover);
+				walrcv_alter_slot(wrconn, opts.slot_name, opts.twophase, opts.failover);
 			}
 		}
 		PG_FINALLY();
@@ -868,7 +869,7 @@ CreateSubscription(ParseState *pstate, CreateSubscriptionStmt *stmt,
 	pgstat_create_subscription(subid);
 
 	if (opts.enabled)
-		ApplyLauncherWakeupAtCommit();
+		ApplyLauncherWakeupAtEOXact(true);
 
 	ObjectAddressSet(myself, SubscriptionRelationId, subid);
 
@@ -1165,7 +1166,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 			{
 				supported_opts = (SUBOPT_SLOT_NAME |
 								  SUBOPT_SYNCHRONOUS_COMMIT | SUBOPT_BINARY |
-								  SUBOPT_STREAMING | SUBOPT_DISABLE_ON_ERR |
+								  SUBOPT_STREAMING | SUBOPT_TWOPHASE_COMMIT |
+								  SUBOPT_DISABLE_ON_ERR |
 								  SUBOPT_PASSWORD_REQUIRED |
 								  SUBOPT_RUN_AS_OWNER | SUBOPT_FAILOVER |
 								  SUBOPT_ORIGIN);
@@ -1173,6 +1175,31 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 				parse_subscription_options(pstate, stmt->options,
 										   supported_opts, &opts);
 
+				/* XXX */
+				if (IsSet(opts.specified_opts, SUBOPT_TWOPHASE_COMMIT))
+				{
+					/* Stop corresponding worker */
+					logicalrep_worker_stop(subid, InvalidOid);
+
+					/* Request to start worker at the end of transaction */
+					ApplyLauncherWakeupAtEOXact(false);
+
+					/* Check whether the number of prepared transactions */
+					if (!opts.twophase &&
+						form->subtwophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
+						LookupGXactBySubid(subid))
+						ereport(ERROR,
+								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+								 errmsg("cannot disable two_phase when uncommitted prepared transactions present")));
+
+					/* Change system catalog acoordingly */
+					values[Anum_pg_subscription_subtwophasestate - 1] =
+						CharGetDatum(opts.twophase ?
+									 LOGICALREP_TWOPHASE_STATE_PENDING :
+									 LOGICALREP_TWOPHASE_STATE_DISABLED);
+					replaces[Anum_pg_subscription_subtwophasestate - 1] = true;
+				}
+
 				if (IsSet(opts.specified_opts, SUBOPT_SLOT_NAME))
 				{
 					/*
@@ -1299,7 +1326,7 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 				replaces[Anum_pg_subscription_subenabled - 1] = true;
 
 				if (opts.enabled)
-					ApplyLauncherWakeupAtCommit();
+					ApplyLauncherWakeupAtEOXact(true);
 
 				update_tuple = true;
 				break;
@@ -1521,7 +1548,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 	 * doing the database operations we won't be able to rollback altered
 	 * slot.
 	 */
-	if (replaces[Anum_pg_subscription_subfailover - 1])
+	if (replaces[Anum_pg_subscription_subtwophasestate - 1] ||
+		replaces[Anum_pg_subscription_subfailover - 1])
 	{
 		bool		must_use_password;
 		char	   *err;
@@ -1541,7 +1569,7 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 
 		PG_TRY();
 		{
-			walrcv_alter_slot(wrconn, sub->slotname, opts.failover);
+			walrcv_alter_slot(wrconn, sub->slotname, opts.twophase, opts.failover);
 		}
 		PG_FINALLY();
 		{
@@ -1962,7 +1990,7 @@ AlterSubscriptionOwner_internal(Relation rel, HeapTuple tup, Oid newOwnerId)
 							  form->oid, 0);
 
 	/* Wake up related background processes to handle this change quickly. */
-	ApplyLauncherWakeupAtCommit();
+	ApplyLauncherWakeupAtEOXact(true);
 	LogicalRepWorkersWakeupAtCommit(form->oid);
 }
 
diff --git a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
index 3c2b1bb496..baef3bdec0 100644
--- a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
+++ b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
@@ -80,7 +80,7 @@ static char *libpqrcv_create_slot(WalReceiverConn *conn,
 								  CRSSnapshotAction snapshot_action,
 								  XLogRecPtr *lsn);
 static void libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-								bool failover);
+								bool two_phase, bool failover);
 static pid_t libpqrcv_get_backend_pid(WalReceiverConn *conn);
 static WalRcvExecResult *libpqrcv_exec(WalReceiverConn *conn,
 									   const char *query,
@@ -1121,14 +1121,15 @@ libpqrcv_create_slot(WalReceiverConn *conn, const char *slotname,
  */
 static void
 libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-					bool failover)
+					bool two_phase, bool failover)
 {
 	StringInfoData cmd;
 	PGresult   *res;
 
 	initStringInfo(&cmd);
-	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( FAILOVER %s )",
+	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( TWO_PHASE %s, FAILOVER %s )",
 					 quote_identifier(slotname),
+					 two_phase ? "true" : "false",
 					 failover ? "true" : "false");
 
 	res = libpqrcv_PQexec(conn->streamConn, cmd.data);
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 66070e9131..3e0e5a77e0 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -89,6 +89,7 @@ static dsa_area *last_start_times_dsa = NULL;
 static dshash_table *last_start_times = NULL;
 
 static bool on_commit_launcher_wakeup = false;
+static bool launcher_wakeup = false;
 
 
 static void ApplyLauncherWakeup(void);
@@ -1085,13 +1086,22 @@ ApplyLauncherForgetWorkerStartTime(Oid subid)
 void
 AtEOXact_ApplyLauncher(bool isCommit)
 {
+	bool		kicked = false;
+
 	if (isCommit)
 	{
 		if (on_commit_launcher_wakeup)
+		{
 			ApplyLauncherWakeup();
+			kicked = true;
+		}
 	}
 
+	if (!kicked && launcher_wakeup)
+		ApplyLauncherWakeup();
+
 	on_commit_launcher_wakeup = false;
+	launcher_wakeup = false;
 }
 
 /*
@@ -1102,10 +1112,15 @@ AtEOXact_ApplyLauncher(bool isCommit)
  * tuple was added to the pg_subscription catalog.
 */
 void
-ApplyLauncherWakeupAtCommit(void)
+ApplyLauncherWakeupAtEOXact(bool on_commit)
 {
-	if (!on_commit_launcher_wakeup)
-		on_commit_launcher_wakeup = true;
+	if (on_commit)
+	{
+		if (!on_commit_launcher_wakeup)
+			on_commit_launcher_wakeup = true;
+	}
+	else if (!launcher_wakeup)
+		launcher_wakeup = true;
 }
 
 static void
diff --git a/src/backend/replication/logical/worker.c b/src/backend/replication/logical/worker.c
index b5a80fe3e8..ca3d260fc3 100644
--- a/src/backend/replication/logical/worker.c
+++ b/src/backend/replication/logical/worker.c
@@ -3911,9 +3911,6 @@ maybe_reread_subscription(void)
 	/* !slotname should never happen when enabled is true. */
 	Assert(newsub->slotname);
 
-	/* two-phase should not be altered */
-	Assert(newsub->twophasestate == MySubscription->twophasestate);
-
 	/*
 	 * Exit if any parameter that affects the remote connection was changed.
 	 * The launcher will start a new worker but note that the parallel apply
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index cebf44bb0f..621f35ab1e 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -800,8 +800,10 @@ ReplicationSlotDrop(const char *name, bool nowait)
  * Change the definition of the slot identified by the specified name.
  */
 void
-ReplicationSlotAlter(const char *name, bool failover)
+ReplicationSlotAlter(const char *name, bool two_phase, bool failover)
 {
+	bool		update_slot = false;
+
 	Assert(MyReplicationSlot == NULL);
 
 	ReplicationSlotAcquire(name, false);
@@ -844,12 +846,27 @@ ReplicationSlotAlter(const char *name, bool failover)
 				errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 				errmsg("cannot enable failover for a temporary replication slot"));
 
+	if (MyReplicationSlot->data.two_phase != two_phase)
+	{
+		SpinLockAcquire(&MyReplicationSlot->mutex);
+		MyReplicationSlot->data.two_phase = two_phase;
+		SpinLockRelease(&MyReplicationSlot->mutex);
+
+		update_slot = true;
+	}
+
+
 	if (MyReplicationSlot->data.failover != failover)
 	{
 		SpinLockAcquire(&MyReplicationSlot->mutex);
 		MyReplicationSlot->data.failover = failover;
 		SpinLockRelease(&MyReplicationSlot->mutex);
 
+		update_slot = true;
+	}
+
+	if (update_slot)
+	{
 		ReplicationSlotMarkDirty();
 		ReplicationSlotSave();
 	}
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index bc40c454de..be155067ce 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1411,14 +1411,25 @@ DropReplicationSlot(DropReplicationSlotCmd *cmd)
  * Process extra options given to ALTER_REPLICATION_SLOT.
  */
 static void
-ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd, bool *failover)
+ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd,
+						  bool *two_phase, bool *failover)
 {
+	bool		two_phase_given = false;
 	bool		failover_given = false;
 
 	/* Parse options */
 	foreach_ptr(DefElem, defel, cmd->options)
 	{
-		if (strcmp(defel->defname, "failover") == 0)
+		if (strcmp(defel->defname, "two_phase") == 0)
+		{
+			if (two_phase_given)
+				ereport(ERROR,
+						(errcode(ERRCODE_SYNTAX_ERROR),
+						 errmsg("conflicting or redundant options")));
+			two_phase_given = true;
+			*two_phase = defGetBoolean(defel);
+		}
+		else if (strcmp(defel->defname, "failover") == 0)
 		{
 			if (failover_given)
 				ereport(ERROR,
@@ -1438,10 +1449,11 @@ ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd, bool *failover)
 static void
 AlterReplicationSlot(AlterReplicationSlotCmd *cmd)
 {
+	bool		two_phase = false;
 	bool		failover = false;
 
-	ParseAlterReplSlotOptions(cmd, &failover);
-	ReplicationSlotAlter(cmd->slotname, failover);
+	ParseAlterReplSlotOptions(cmd, &two_phase, &failover);
+	ReplicationSlotAlter(cmd->slotname, two_phase, failover);
 }
 
 /*
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
index 6fee3160f0..5ff84301cd 100644
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -1948,7 +1948,7 @@ psql_completion(const char *text, int start, int end)
 	else if (HeadMatches("ALTER", "SUBSCRIPTION", MatchAny) && TailMatches("SET", "("))
 		COMPLETE_WITH("binary", "disable_on_error", "failover", "origin",
 					  "password_required", "run_as_owner", "slot_name",
-					  "streaming", "synchronous_commit");
+					  "streaming", "synchronous_commit", "two_phase");
 	/* ALTER SUBSCRIPTION <name> SKIP ( */
 	else if (HeadMatches("ALTER", "SUBSCRIPTION", MatchAny) && TailMatches("SKIP", "("))
 		COMPLETE_WITH("lsn");
diff --git a/src/include/access/twophase.h b/src/include/access/twophase.h
index 56248c0006..d493ed24c5 100644
--- a/src/include/access/twophase.h
+++ b/src/include/access/twophase.h
@@ -62,4 +62,7 @@ extern void PrepareRedoRemove(TransactionId xid, bool giveWarning);
 extern void restoreTwoPhaseData(void);
 extern bool LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 						TimestampTz origin_prepare_timestamp);
+
+extern bool LookupGXactBySubid(Oid subid);
+
 #endif							/* TWOPHASE_H */
diff --git a/src/include/replication/logicallauncher.h b/src/include/replication/logicallauncher.h
index ff0438b5bb..075842c67e 100644
--- a/src/include/replication/logicallauncher.h
+++ b/src/include/replication/logicallauncher.h
@@ -24,7 +24,7 @@ extern void ApplyLauncherShmemInit(void);
 
 extern void ApplyLauncherForgetWorkerStartTime(Oid subid);
 
-extern void ApplyLauncherWakeupAtCommit(void);
+extern void ApplyLauncherWakeupAtEOXact(bool on_commit);
 extern void AtEOXact_ApplyLauncher(bool isCommit);
 
 extern bool IsLogicalLauncher(void);
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 7b937d1a0c..2fcb11418f 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -243,7 +243,8 @@ extern void ReplicationSlotCreate(const char *name, bool db_specific,
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
 extern void ReplicationSlotDropAcquired(void);
-extern void ReplicationSlotAlter(const char *name, bool failover);
+extern void ReplicationSlotAlter(const char *name, bool two_phase,
+								 bool failover);
 
 extern void ReplicationSlotAcquire(const char *name, bool nowait);
 extern void ReplicationSlotRelease(void);
diff --git a/src/include/replication/walreceiver.h b/src/include/replication/walreceiver.h
index 12f71fa99b..a443f402f5 100644
--- a/src/include/replication/walreceiver.h
+++ b/src/include/replication/walreceiver.h
@@ -377,6 +377,7 @@ typedef char *(*walrcv_create_slot_fn) (WalReceiverConn *conn,
  */
 typedef void (*walrcv_alter_slot_fn) (WalReceiverConn *conn,
 									  const char *slotname,
+									  bool two_phase,
 									  bool failover);
 
 /*
@@ -455,8 +456,8 @@ extern PGDLLIMPORT WalReceiverFunctionsType *WalReceiverFunctions;
 	WalReceiverFunctions->walrcv_send(conn, buffer, nbytes)
 #define walrcv_create_slot(conn, slotname, temporary, two_phase, failover, snapshot_action, lsn) \
 	WalReceiverFunctions->walrcv_create_slot(conn, slotname, temporary, two_phase, failover, snapshot_action, lsn)
-#define walrcv_alter_slot(conn, slotname, failover) \
-	WalReceiverFunctions->walrcv_alter_slot(conn, slotname, failover)
+#define walrcv_alter_slot(conn, slotname, two_phase, failover) \
+	WalReceiverFunctions->walrcv_alter_slot(conn, slotname, two_phase, failover)
 #define walrcv_get_backend_pid(conn) \
 	WalReceiverFunctions->walrcv_get_backend_pid(conn)
 #define walrcv_exec(conn, exec, nRetTypes, retTypes) \
diff --git a/src/test/regress/expected/subscription.out b/src/test/regress/expected/subscription.out
index 1eee6b17b8..9bba656e00 100644
--- a/src/test/regress/expected/subscription.out
+++ b/src/test/regress/expected/subscription.out
@@ -379,10 +379,7 @@ HINT:  To initiate replication, you must manually create the replication slot, e
  regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | p                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
---fail - alter of two_phase option not supported.
-ALTER SUBSCRIPTION regress_testsub SET (two_phase = false);
-ERROR:  unrecognized subscription parameter: "two_phase"
--- but can alter streaming when two_phase enabled
+-- We can alter streaming when two_phase enabled
 ALTER SUBSCRIPTION regress_testsub SET (streaming = true);
 \dRs+
                                                                                                                 List of subscriptions
diff --git a/src/test/regress/sql/subscription.sql b/src/test/regress/sql/subscription.sql
index 1b2a23ba7b..9ff151f806 100644
--- a/src/test/regress/sql/subscription.sql
+++ b/src/test/regress/sql/subscription.sql
@@ -257,10 +257,7 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUBLICATION testpub WITH (connect = false, two_phase = true);
 
 \dRs+
---fail - alter of two_phase option not supported.
-ALTER SUBSCRIPTION regress_testsub SET (two_phase = false);
-
--- but can alter streaming when two_phase enabled
+-- We can alter streaming when two_phase enabled
 ALTER SUBSCRIPTION regress_testsub SET (streaming = true);
 
 \dRs+
-- 
2.43.0

From e5da6b142c6bcfb2943cdc24c6d63bf110dcf75e Mon Sep 17 00:00:00 2001
From: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Date: Mon, 8 Apr 2024 02:32:38 +0000
Subject: [PATCH v3 2/5] Mandate the subscription has been disabled

---
 doc/src/sgml/ref/alter_subscription.sgml   |  6 ++++--
 src/backend/commands/subscriptioncmds.c    | 20 ++++++++++++--------
 src/backend/replication/logical/launcher.c | 21 +++------------------
 src/backend/replication/logical/worker.c   |  3 +++
 src/include/replication/logicallauncher.h  |  2 +-
 5 files changed, 23 insertions(+), 29 deletions(-)

diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index 413ce68ce2..20b45e36e0 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -227,9 +227,11 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-disable-on-error"><literal>disable_on_error</literal></link>,
       <link linkend="sql-createsubscription-params-with-password-required"><literal>password_required</literal></link>,
       <link linkend="sql-createsubscription-params-with-run-as-owner"><literal>run_as_owner</literal></link>,
-      <link linkend="sql-createsubscription-params-with-origin"><literal>origin</literal></link>, and
-      <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>.
+      <link linkend="sql-createsubscription-params-with-origin"><literal>origin</literal></link>,
+      <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>, and
+      <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>.
       Only a superuser can set <literal>password_required = false</literal>.
+      <literal>two_phase</literal> can be altered only for disabled subscription.
      </para>
 
      <para>
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index 6643fc08a6..bfbb2873b1 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -869,7 +869,7 @@ CreateSubscription(ParseState *pstate, CreateSubscriptionStmt *stmt,
 	pgstat_create_subscription(subid);
 
 	if (opts.enabled)
-		ApplyLauncherWakeupAtEOXact(true);
+		ApplyLauncherWakeupAtCommit();
 
 	ObjectAddressSet(myself, SubscriptionRelationId, subid);
 
@@ -1178,11 +1178,15 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 				/* XXX */
 				if (IsSet(opts.specified_opts, SUBOPT_TWOPHASE_COMMIT))
 				{
-					/* Stop corresponding worker */
-					logicalrep_worker_stop(subid, InvalidOid);
-
-					/* Request to start worker at the end of transaction */
-					ApplyLauncherWakeupAtEOXact(false);
+					/*
+					 * two_phase can be only changed for disabled
+					 * subscriptions
+					 */
+					if (form->subenabled)
+						ereport(ERROR,
+								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+								 errmsg("cannot set %s for enabled subscription",
+										"two_phase")));
 
 					/* Check whether the number of prepared transactions */
 					if (!opts.twophase &&
@@ -1326,7 +1330,7 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 				replaces[Anum_pg_subscription_subenabled - 1] = true;
 
 				if (opts.enabled)
-					ApplyLauncherWakeupAtEOXact(true);
+					ApplyLauncherWakeupAtCommit();
 
 				update_tuple = true;
 				break;
@@ -1990,7 +1994,7 @@ AlterSubscriptionOwner_internal(Relation rel, HeapTuple tup, Oid newOwnerId)
 							  form->oid, 0);
 
 	/* Wake up related background processes to handle this change quickly. */
-	ApplyLauncherWakeupAtEOXact(true);
+	ApplyLauncherWakeupAtCommit();
 	LogicalRepWorkersWakeupAtCommit(form->oid);
 }
 
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 3e0e5a77e0..66070e9131 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -89,7 +89,6 @@ static dsa_area *last_start_times_dsa = NULL;
 static dshash_table *last_start_times = NULL;
 
 static bool on_commit_launcher_wakeup = false;
-static bool launcher_wakeup = false;
 
 
 static void ApplyLauncherWakeup(void);
@@ -1086,22 +1085,13 @@ ApplyLauncherForgetWorkerStartTime(Oid subid)
 void
 AtEOXact_ApplyLauncher(bool isCommit)
 {
-	bool		kicked = false;
-
 	if (isCommit)
 	{
 		if (on_commit_launcher_wakeup)
-		{
 			ApplyLauncherWakeup();
-			kicked = true;
-		}
 	}
 
-	if (!kicked && launcher_wakeup)
-		ApplyLauncherWakeup();
-
 	on_commit_launcher_wakeup = false;
-	launcher_wakeup = false;
 }
 
 /*
@@ -1112,15 +1102,10 @@ AtEOXact_ApplyLauncher(bool isCommit)
  * tuple was added to the pg_subscription catalog.
 */
 void
-ApplyLauncherWakeupAtEOXact(bool on_commit)
+ApplyLauncherWakeupAtCommit(void)
 {
-	if (on_commit)
-	{
-		if (!on_commit_launcher_wakeup)
-			on_commit_launcher_wakeup = true;
-	}
-	else if (!launcher_wakeup)
-		launcher_wakeup = true;
+	if (!on_commit_launcher_wakeup)
+		on_commit_launcher_wakeup = true;
 }
 
 static void
diff --git a/src/backend/replication/logical/worker.c b/src/backend/replication/logical/worker.c
index ca3d260fc3..374aa22091 100644
--- a/src/backend/replication/logical/worker.c
+++ b/src/backend/replication/logical/worker.c
@@ -3911,6 +3911,9 @@ maybe_reread_subscription(void)
 	/* !slotname should never happen when enabled is true. */
 	Assert(newsub->slotname);
 
+	/* two-phase should not be altered while the worker exists */
+	Assert(newsub->twophasestate == MySubscription->twophasestate);
+
 	/*
 	 * Exit if any parameter that affects the remote connection was changed.
 	 * The launcher will start a new worker but note that the parallel apply
diff --git a/src/include/replication/logicallauncher.h b/src/include/replication/logicallauncher.h
index 075842c67e..ff0438b5bb 100644
--- a/src/include/replication/logicallauncher.h
+++ b/src/include/replication/logicallauncher.h
@@ -24,7 +24,7 @@ extern void ApplyLauncherShmemInit(void);
 
 extern void ApplyLauncherForgetWorkerStartTime(Oid subid);
 
-extern void ApplyLauncherWakeupAtEOXact(bool on_commit);
+extern void ApplyLauncherWakeupAtCommit(void);
 extern void AtEOXact_ApplyLauncher(bool isCommit);
 
 extern bool IsLogicalLauncher(void);
-- 
2.43.0

From 929515539b0919d560088f97d89b02376ca5492b Mon Sep 17 00:00:00 2001
From: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Date: Mon, 8 Apr 2024 12:39:12 +0000
Subject: [PATCH v3 3/5] Prohibit altering from true to false if there are
 prepared transactions on subscriber

---
 doc/src/sgml/ref/alter_subscription.sgml |  8 +++++++-
 src/backend/access/transam/twophase.c    |  4 +++-
 src/backend/commands/subscriptioncmds.c  | 13 ++++++++++---
 3 files changed, 20 insertions(+), 5 deletions(-)

diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index 20b45e36e0..4f33769858 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -231,7 +231,6 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>, and
       <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>.
       Only a superuser can set <literal>password_required = false</literal>.
-      <literal>two_phase</literal> can be altered only for disabled subscription.
      </para>
 
      <para>
@@ -253,6 +252,13 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>
       option is enabled.
      </para>
+
+     <para>
+      <literal>two_phase</literal> can be altered only for disabled
+      subscriptions.  Prepared transactions done by the logical replication
+      worker must not be existed. If found, the <command>ALTER
+      SUBSCRIPTION</command> command will fail.
+     </para>
     </listitem>
    </varlistentry>
 
diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index 495f99a357..34bf6bfb0b 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -2703,7 +2703,7 @@ checkGid(char *gid, Oid subid)
 
 /*
  * LookupGXactBySubid
- *		Check if the prepared transaction done by apply worker exists.
+ *      Check if the prepared transaction done by the given subscription.
  */
 bool
 LookupGXactBySubid(Oid subid)
@@ -2721,7 +2721,9 @@ LookupGXactBySubid(Oid subid)
 			found = true;
 			break;
 		}
+
 	}
 	LWLockRelease(TwoPhaseStateLock);
+
 	return found;
 }
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index bfbb2873b1..563c757be5 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -1188,13 +1188,20 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 								 errmsg("cannot set %s for enabled subscription",
 										"two_phase")));
 
-					/* Check whether the number of prepared transactions */
+					/*
+					 * If the two_phase is altered from true to false,
+					 * prepared transactions shipped from the publisher won't
+					 * be resolved anymore. Therefore, reject the ALTER
+					 * command if they exists.
+					 */
 					if (!opts.twophase &&
 						form->subtwophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
-						LookupGXactBySubid(subid))
+						LookupGXactBySubid(form->oid))
 						ereport(ERROR,
 								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-								 errmsg("cannot disable two_phase when uncommitted prepared transactions present")));
+								 errmsg("cannot alter %s to false if there are prepared transactions by the subscription",
+										"two_phase")));
+
 
 					/* Change system catalog acoordingly */
 					values[Anum_pg_subscription_subtwophasestate - 1] =
-- 
2.43.0

From 3a7125c89de3d6fd6c1081e1100476e99d74c9c1 Mon Sep 17 00:00:00 2001
From: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Date: Mon, 15 Apr 2024 04:58:29 +0000
Subject: [PATCH v3 4/5] Prohibit altering from false to true if there are
 prepared transactions on publisher

---
 doc/src/sgml/ref/alter_subscription.sgml |  9 +--
 src/backend/commands/subscriptioncmds.c  | 73 ++++++++++++++++++++++++
 2 files changed, 78 insertions(+), 4 deletions(-)

diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index 4f33769858..12d6ca2f5e 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -254,10 +254,11 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
      </para>
 
      <para>
-      <literal>two_phase</literal> can be altered only for disabled
-      subscriptions.  Prepared transactions done by the logical replication
-      worker must not be existed. If found, the <command>ALTER
-      SUBSCRIPTION</command> command will fail.
+      On the publisher side, any prepared transactions must not exist.  On the
+      subscriber side, prepared transactions done by the logical replication
+      worker must not exist. Prepared transactions done by users are allowed.
+      The <command>ALTER SUBSCRIPTION</command> command will fail if they are
+      found.
      </para>
     </listitem>
    </varlistentry>
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index 563c757be5..57d2e615c6 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -110,6 +110,7 @@ static void check_publications_origin(WalReceiverConn *wrconn,
 static void check_duplicates_in_publist(List *publist, Datum *datums);
 static List *merge_publications(List *oldpublist, List *newpublist, bool addpub, const char *subname);
 static void ReportSlotConnectionError(List *rstates, Oid subid, char *slotname, char *err);
+static bool IsPreparedTransactionExistsOnPublisher(Subscription *sub);
 
 
 /*
@@ -1202,6 +1203,24 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 								 errmsg("cannot alter %s to false if there are prepared transactions by the subscription",
 										"two_phase")));
 
+					/*
+					 * Suppose the two_phase is altering from false to true,
+					 * and there have been prepared transactions on the
+					 * publisher. In that case, only the COMMIT PREPARED
+					 * record may be decoded and sent to the subscriber. It
+					 * occurs because confirmed_flush_lsn can be ahead of the
+					 * PREPARE record, so decoding all the transactions might
+					 * be skipped after enabling the subscription.
+					 *
+					 * We prohibit the existing prepared transactions on the
+					 * publisher to avoid the issue.
+					 */
+					else if (opts.twophase &&
+							 IsPreparedTransactionExistsOnPublisher(sub))
+						ereport(ERROR,
+								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+								 errmsg("cannot alter %s to true if there are prepared transactions on publisher",
+										"two_phase")));
 
 					/* Change system catalog acoordingly */
 					values[Anum_pg_subscription_subtwophasestate - 1] =
@@ -2489,3 +2508,57 @@ defGetStreamingMode(DefElem *def)
 					def->defname)));
 	return LOGICALREP_STREAM_OFF;	/* keep compiler quiet */
 }
+
+/*
+ * Check whether there are prepared transactions on the publisher node. Returns
+ * true if exists, otherwise false.
+ */
+static bool
+IsPreparedTransactionExistsOnPublisher(Subscription *sub)
+{
+	bool		must_use_password;
+	bool		found = false;
+	WalReceiverConn *wrconn;
+	WalRcvExecResult *res;
+	char	   *err;
+	StringInfo	cmd;
+	Oid			tableRow[1] = {INT4OID};
+
+	/* Load the library providing us libpq calls. */
+	load_file("libpqwalreceiver", false);
+	/* Try to connect to the publisher. */
+	must_use_password = (!superuser_arg(GetUserId()) &&
+						 sub->passwordrequired);
+	wrconn = walrcv_connect(sub->conninfo, true, true,
+							must_use_password,
+							sub->name, &err);
+	if (!wrconn)
+		ereport(ERROR,
+				(errcode(ERRCODE_CONNECTION_FAILURE),
+				 errmsg("could not connect to the publisher: %s", err)));
+
+	/* Construct a query and execute it */
+	cmd = makeStringInfo();
+	appendStringInfo(cmd,
+					 "SELECT 1 FROM pg_prepared_xacts WHERE database = '%s'",
+					 get_database_name(sub->dbid));
+
+	res = walrcv_exec(wrconn, cmd->data, 1, tableRow);
+	destroyStringInfo(cmd);
+
+	if (res->status != WALRCV_OK_TUPLES)
+		ereport(ERROR,
+				errmsg("could not fetch number of prepared transactions from the primary server: %s",
+					   res->err));
+
+	/*
+	 * We are only interested in the existence of prepared transactions.
+	 * Hence, it is sufficient to check the number of returned rows.
+	 */
+	if (tuplestore_tuple_count(res->tuplestore) > 1)
+		found = true;
+
+	walrcv_clear_result(res);
+
+	return found;
+}
-- 
2.43.0

From 0fedd27b5a9d01cc6ea65bedb8bbb3bf765ca1ec Mon Sep 17 00:00:00 2001
From: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Date: Mon, 15 Apr 2024 05:40:07 +0000
Subject: [PATCH v3 5/5] Add TAP tests for altering two_phase option

---
 src/test/subscription/t/021_twophase.pl | 66 ++++++++++++++++++++++++-
 1 file changed, 64 insertions(+), 2 deletions(-)

diff --git a/src/test/subscription/t/021_twophase.pl b/src/test/subscription/t/021_twophase.pl
index 9437cd4c3b..1937905493 100644
--- a/src/test/subscription/t/021_twophase.pl
+++ b/src/test/subscription/t/021_twophase.pl
@@ -367,6 +367,70 @@ $result =
   $node_subscriber->safe_psql('postgres', "SELECT count(*) FROM tab_copy;");
 is($result, qq(2), 'replicated data in subscriber table');
 
+# Disable the subscription and alter it to two_phase = false,
+# verify that the altered subscription reflects the two_phase option.
+
+# Alter subscription two_phase to false
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy DISABLE");
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = false)");
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy ENABLE");
+
+# Wait for subscription startup
+$node_subscriber->wait_for_subscription_sync($node_publisher, $appname_copy);
+
+# Make sure that the two-phase is disabled on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT subtwophasestate FROM pg_subscription WHERE subname = 'tap_sub_copy';"
+);
+is($result, qq(d), 'two-phase is disabled');
+
+# Now do a prepare on publisher and make sure that it is not replicated.
+$node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub");
+$node_publisher->safe_psql(
+	'postgres', "
+    BEGIN;
+    INSERT INTO tab_copy VALUES (100);
+    PREPARE TRANSACTION 'newgid';");
+
+# Wait for the subscriber to catchup
+$node_publisher->wait_for_catchup($appname_copy);
+
+# Make sure that there is 0 prepared transaction on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT count(*) FROM pg_prepared_xacts;");
+is($result, qq(0), 'transaction is prepared on subscriber');
+
+# Now commit the insert and verify that it IS replicated
+$node_publisher->safe_psql('postgres', "COMMIT PREPARED 'newgid';");
+
+# Wait for the subscriber to catchup
+$node_publisher->wait_for_catchup($appname_copy);
+
+# made sure that the commited transaction is replicated.
+$result =
+  $node_subscriber->safe_psql('postgres', "SELECT count(*) FROM tab_copy;");
+is($result, qq(3), 'replicated data in subscriber table');
+
+# Alter subscription two_phase to true
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy DISABLE");
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = true)");
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy ENABLE");
+
+# Wait for subscription startup
+$node_subscriber->wait_for_subscription_sync($node_publisher, $appname_copy);
+
+# Make sure that the two-phase is enabled on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT subtwophasestate FROM pg_subscription WHERE subname = 'tap_sub_copy';"
+);
+is($result, qq(e), 'two-phase is disabled');
+
 $node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub_copy;");
 $node_publisher->safe_psql('postgres', "DROP PUBLICATION tap_pub_copy;");
 
@@ -374,8 +438,6 @@ $node_publisher->safe_psql('postgres', "DROP PUBLICATION tap_pub_copy;");
 # check all the cleanup
 ###############################
 
-$node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub");
-
 $result = $node_subscriber->safe_psql('postgres',
 	"SELECT count(*) FROM pg_subscription");
 is($result, qq(0), 'check subscription was dropped on subscriber');
-- 
2.43.0

From 5e4e79a5056bae374911d96eef6c4d945e23903e Mon Sep 17 00:00:00 2001
From: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Date: Wed, 17 Apr 2024 06:18:23 +0000
Subject: [PATCH v4 2/3] Alter slot option two_phase only when altering true to
 false

---
 src/backend/commands/subscriptioncmds.c       | 21 +++++-
 .../libpqwalreceiver/libpqwalreceiver.c       | 21 ++++--
 src/include/replication/walreceiver.h         |  8 +--
 src/test/subscription/meson.build             |  1 +
 src/test/subscription/t/099_twophase_added.pl | 72 +++++++++++++++++++
 5 files changed, 111 insertions(+), 12 deletions(-)
 create mode 100644 src/test/subscription/t/099_twophase_added.pl

diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index 3299a60fff..0d80d6e110 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -850,7 +850,7 @@ CreateSubscription(ParseState *pstate, CreateSubscriptionStmt *stmt,
 			else if (opts.slot_name &&
 					 (opts.failover || walrcv_server_version(wrconn) >= 170000))
 			{
-				walrcv_alter_slot(wrconn, opts.slot_name, opts.twophase, opts.failover);
+				walrcv_alter_slot(wrconn, opts.slot_name, NULL, &opts.failover);
 			}
 		}
 		PG_FINALLY();
@@ -1564,6 +1564,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 		bool		must_use_password;
 		char	   *err;
 		WalReceiverConn *wrconn;
+		bool		two_phase_needs_to_be_updated;
+		bool		failover_needs_to_be_updated;
 
 		/* Load the library providing us libpq calls. */
 		load_file("libpqwalreceiver", false);
@@ -1577,9 +1579,24 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 					(errcode(ERRCODE_CONNECTION_FAILURE),
 					 errmsg("could not connect to the publisher: %s", err)));
 
+		/*
+		 * Consider which slot option must be altered.
+		 *
+		 * We must alter the failover option whenever subfailover is updated.
+		 * Two_phase, however, is altered only when changing true to false.
+		 */
+		two_phase_needs_to_be_updated =
+						(replaces[Anum_pg_subscription_subtwophasestate - 1] &&
+						 !opts.twophase);
+		failover_needs_to_be_updated =
+								replaces[Anum_pg_subscription_subfailover - 1];
+
 		PG_TRY();
 		{
-			walrcv_alter_slot(wrconn, sub->slotname, opts.twophase, opts.failover);
+			if (two_phase_needs_to_be_updated || failover_needs_to_be_updated)
+				walrcv_alter_slot(wrconn, sub->slotname,
+								  two_phase_needs_to_be_updated ? &opts.twophase : NULL,
+								  failover_needs_to_be_updated ? &opts.failover : NULL);
 		}
 		PG_FINALLY();
 		{
diff --git a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
index baef3bdec0..546b599848 100644
--- a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
+++ b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
@@ -80,7 +80,7 @@ static char *libpqrcv_create_slot(WalReceiverConn *conn,
 								  CRSSnapshotAction snapshot_action,
 								  XLogRecPtr *lsn);
 static void libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-								bool two_phase, bool failover);
+								const bool *two_phase, const bool *failover);
 static pid_t libpqrcv_get_backend_pid(WalReceiverConn *conn);
 static WalRcvExecResult *libpqrcv_exec(WalReceiverConn *conn,
 									   const char *query,
@@ -1121,16 +1121,25 @@ libpqrcv_create_slot(WalReceiverConn *conn, const char *slotname,
  */
 static void
 libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-					bool two_phase, bool failover)
+					const bool *two_phase, const bool *failover)
 {
 	StringInfoData cmd;
 	PGresult   *res;
 
 	initStringInfo(&cmd);
-	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( TWO_PHASE %s, FAILOVER %s )",
-					 quote_identifier(slotname),
-					 two_phase ? "true" : "false",
-					 failover ? "true" : "false");
+	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( ",
+					 quote_identifier(slotname));
+
+	if (two_phase)
+		appendStringInfo(&cmd, "TWO_PHASE %s%s ",
+						 (*two_phase) ? "true" : "false",
+						 failover ? ", " : "");
+
+	if (failover)
+		appendStringInfo(&cmd, "FAILOVER %s ",
+						 (*failover) ? "true" : "false");
+
+	appendStringInfoString(&cmd, ");");
 
 	res = libpqrcv_PQexec(conn->streamConn, cmd.data);
 	pfree(cmd.data);
diff --git a/src/include/replication/walreceiver.h b/src/include/replication/walreceiver.h
index a443f402f5..f30637aa4a 100644
--- a/src/include/replication/walreceiver.h
+++ b/src/include/replication/walreceiver.h
@@ -372,13 +372,13 @@ typedef char *(*walrcv_create_slot_fn) (WalReceiverConn *conn,
 /*
  * walrcv_alter_slot_fn
  *
- * Change the definition of a replication slot. Currently, it only supports
- * changing the failover property of the slot.
+ * Change the definition of a replication slot. Currently, it supports
+ * changing the two_phase and the failover property of the slot.
  */
 typedef void (*walrcv_alter_slot_fn) (WalReceiverConn *conn,
 									  const char *slotname,
-									  bool two_phase,
-									  bool failover);
+									  const bool *two_phase,
+									  const bool *failover);
 
 /*
  * walrcv_get_backend_pid_fn
diff --git a/src/test/subscription/meson.build b/src/test/subscription/meson.build
index c591cd7d61..b4bd522c3d 100644
--- a/src/test/subscription/meson.build
+++ b/src/test/subscription/meson.build
@@ -40,6 +40,7 @@ tests += {
       't/031_column_list.pl',
       't/032_subscribe_use_index.pl',
       't/033_run_as_table_owner.pl',
+      't/099_twophase_added.pl',
       't/100_bugs.pl',
     ],
   },
diff --git a/src/test/subscription/t/099_twophase_added.pl b/src/test/subscription/t/099_twophase_added.pl
new file mode 100644
index 0000000000..c13a37675a
--- /dev/null
+++ b/src/test/subscription/t/099_twophase_added.pl
@@ -0,0 +1,72 @@
+# Copyright (c) 2021-2024, PostgreSQL Global Development Group
+
+# Additional tests for altering two_phase option
+use strict;
+use warnings FATAL => 'all';
+use PostgreSQL::Test::Cluster;
+use PostgreSQL::Test::Utils;
+use Test::More;
+
+# Initialize publisher node
+my $node_publisher = PostgreSQL::Test::Cluster->new('publisher');
+$node_publisher->init(allows_streaming => 'logical');
+$node_publisher->append_conf('postgresql.conf',
+	qq(max_prepared_transactions = 10));
+$node_publisher->start;
+
+# Create subscriber node
+my $node_subscriber = PostgreSQL::Test::Cluster->new('subscriber');
+$node_subscriber->init;
+$node_subscriber->append_conf('postgresql.conf',
+	qq(max_prepared_transactions = 10));
+$node_subscriber->start;
+
+# Define pre-existing tables on both nodes
+$node_publisher->safe_psql('postgres',
+    "CREATE TABLE tab_full (a int PRIMARY KEY);");
+$node_subscriber->safe_psql('postgres',
+	"CREATE TABLE tab_full (a int PRIMARY KEY)");
+
+# Setup logical replication, with two_phase = off
+my $publisher_connstr = $node_publisher->connstr . ' dbname=postgres';
+$node_publisher->safe_psql('postgres',
+	"CREATE PUBLICATION pub FOR ALL TABLES");
+
+$node_subscriber->safe_psql(
+	'postgres', "
+	CREATE SUBSCRIPTION sub
+	CONNECTION '$publisher_connstr' PUBLICATION pub
+	WITH (two_phase = off, copy_data = off)");
+
+######
+# Check the case that prepared transactions exist on publisher node
+######
+
+$node_publisher->safe_psql(
+	'postgres', "
+	BEGIN;
+	INSERT INTO tab_full VALUES (generate_series(1, 5));
+	PREPARE TRANSACTION 'test_prepared_tab_full';");
+
+$node_publisher->wait_for_catchup('sub');
+
+my $result = $node_subscriber->safe_psql('postgres',
+    "SELECT count(*) FROM pg_prepared_xacts;");
+is($result, q(0), "transaction is not prepared on subscriber");
+
+$node_subscriber->safe_psql(
+    'postgres', "
+    ALTER SUBSCRIPTION sub DISABLE;
+    ALTER SUBSCRIPTION sub SET (two_phase = on);
+    ALTER SUBSCRIPTION sub ENABLE;");
+
+$node_publisher->safe_psql( 'postgres',
+    "COMMIT PREPARED 'test_prepared_tab_full';");
+$node_publisher->wait_for_catchup('sub');
+
+$result = $node_subscriber->safe_psql('postgres',
+    "SELECT count(*) FROM tab_full;");
+is($result, q(5),
+   "prepared transactions done before altering can be replicated");
+
+done_testing();
-- 
2.43.0

From 35d6a2a4f3ffe42aeebb56f219cd7004777baf10 Mon Sep 17 00:00:00 2001
From: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Date: Mon, 8 Apr 2024 12:39:12 +0000
Subject: [PATCH v4 3/3] Abort prepared transactions while altering two_phase
 to false

---
 doc/src/sgml/ref/alter_subscription.sgml      | 10 +++++-
 src/backend/access/transam/twophase.c         | 19 +++++-----
 src/backend/commands/subscriptioncmds.c       | 27 +++++++++++---
 src/include/access/twophase.h                 |  3 +-
 src/test/subscription/t/099_twophase_added.pl | 35 +++++++++++++++++++
 5 files changed, 77 insertions(+), 17 deletions(-)

diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index 20b45e36e0..cfd2a18e2c 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -231,7 +231,6 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>, and
       <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>.
       Only a superuser can set <literal>password_required = false</literal>.
-      <literal>two_phase</literal> can be altered only for disabled subscription.
      </para>
 
      <para>
@@ -253,6 +252,15 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>
       option is enabled.
      </para>
+
+     <para>
+      <literal>two_phase</literal> can be altered only for disabled
+      subscriptions. When altering the parameter from <literal>true</literal>
+      to <literal>false</literal>,  the backend process checks prepared
+      transactions done by the logical replication worker and aborts them. If
+      prepared transactions are found, the parameter cannot be altered to
+      <literal>false</literal> inside a transaction block.
+     </para>
     </listitem>
    </varlistentry>
 
diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index 495f99a357..9121195725 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -2702,13 +2702,13 @@ checkGid(char *gid, Oid subid)
 }
 
 /*
- * LookupGXactBySubid
- *		Check if the prepared transaction done by apply worker exists.
+ * GetGidListBySubid
+ *      Get a list of GIDs which is PREPARE'd by the given subscription.
  */
-bool
-LookupGXactBySubid(Oid subid)
+List *
+GetGidListBySubid(Oid subid)
 {
-	bool		found = false;
+	List *list = NIL;
 
 	LWLockAcquire(TwoPhaseStateLock, LW_SHARED);
 	for (int i = 0; i < TwoPhaseState->numPrepXacts; i++)
@@ -2717,11 +2717,10 @@ LookupGXactBySubid(Oid subid)
 
 		/* Ignore not-yet-valid GIDs. */
 		if (gxact->valid && checkGid(gxact->gid, subid))
-		{
-			found = true;
-			break;
-		}
+			list = lappend(list, pstrdup(gxact->gid));
+
 	}
 	LWLockRelease(TwoPhaseStateLock);
-	return found;
+
+	return list;
 }
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index 0d80d6e110..cf3e5c64b0 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -1178,6 +1178,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 				/* XXX */
 				if (IsSet(opts.specified_opts, SUBOPT_TWOPHASE_COMMIT))
 				{
+					List *prepared_xacts = NIL;
+
 					/*
 					 * two_phase can be only changed for disabled
 					 * subscriptions
@@ -1194,13 +1196,28 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 					 */
 					logicalrep_workers_stop(subid);
 
-					/* Check whether the number of prepared transactions */
+					/*
+					 * If two phase was enabled, there is a possibility the
+					 * transactions has already been PREPARE'd.
+					 */
 					if (!opts.twophase &&
 						form->subtwophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
-						LookupGXactBySubid(subid))
-						ereport(ERROR,
-								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-								 errmsg("cannot disable two_phase when uncommitted prepared transactions present")));
+						(prepared_xacts = GetGidListBySubid(subid)) != NIL)
+					{
+						ListCell	*cell;
+
+						/* Must not be in the transaction */
+						PreventInTransactionBlock(isTopLevel,
+												  "ALTER SUBSCRIPTION ... SET (two_phase = ...)");
+
+						/* Abort all listed transactions */
+						foreach(cell, prepared_xacts)
+						{
+							FinishPreparedTransaction((char *) lfirst(cell),
+													  false);
+							prepared_xacts = list_delete_cell(prepared_xacts, cell);
+						}
+					}
 
 					/* Change system catalog acoordingly */
 					values[Anum_pg_subscription_subtwophasestate - 1] =
diff --git a/src/include/access/twophase.h b/src/include/access/twophase.h
index d493ed24c5..95770bbd69 100644
--- a/src/include/access/twophase.h
+++ b/src/include/access/twophase.h
@@ -18,6 +18,7 @@
 #include "access/xlogdefs.h"
 #include "datatype/timestamp.h"
 #include "storage/lock.h"
+#include "nodes/pg_list.h"
 
 /*
  * GlobalTransactionData is defined in twophase.c; other places have no
@@ -63,6 +64,6 @@ extern void restoreTwoPhaseData(void);
 extern bool LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 						TimestampTz origin_prepare_timestamp);
 
-extern bool LookupGXactBySubid(Oid subid);
+extern List *GetGidListBySubid(Oid subid);
 
 #endif							/* TWOPHASE_H */
diff --git a/src/test/subscription/t/099_twophase_added.pl b/src/test/subscription/t/099_twophase_added.pl
index c13a37675a..a8135b671c 100644
--- a/src/test/subscription/t/099_twophase_added.pl
+++ b/src/test/subscription/t/099_twophase_added.pl
@@ -69,4 +69,39 @@ $result = $node_subscriber->safe_psql('postgres',
 is($result, q(5),
    "prepared transactions done before altering can be replicated");
 
+######
+# Check the case that prepared transactions exist on subscriber node
+######
+
+$node_publisher->safe_psql(
+	'postgres', "
+	BEGIN;
+	INSERT INTO tab_full VALUES (generate_series(6, 10));
+	PREPARE TRANSACTION 'test_prepared_tab_full';");
+
+$node_publisher->wait_for_catchup('sub');
+
+$result = $node_subscriber->safe_psql('postgres',
+    "SELECT count(*) FROM pg_prepared_xacts;");
+is($result, q(1), "transaction has been prepared on subscriber");
+
+$node_subscriber->safe_psql(
+    'postgres', "
+    ALTER SUBSCRIPTION sub DISABLE;
+    ALTER SUBSCRIPTION sub SET (two_phase = off);
+    ALTER SUBSCRIPTION sub ENABLE;");
+
+$result = $node_subscriber->safe_psql('postgres',
+    "SELECT count(*) FROM pg_prepared_xacts;");
+is($result, q(0), "prepared transaction done by worker is aborted");
+
+$node_publisher->safe_psql( 'postgres',
+    "COMMIT PREPARED 'test_prepared_tab_full';");
+$node_publisher->wait_for_catchup('sub');
+
+$result = $node_subscriber->safe_psql('postgres',
+    "SELECT count(10) FROM tab_full;");
+is($result, q(10),
+   "prepared transactions on publisher can be replicated");
+
 done_testing();
-- 
2.43.0

From 8295540696e9699ac8191f1c2b0e09b6b684cb50 Mon Sep 17 00:00:00 2001
From: Ajin Cherian <ajinc@fast.au.fujitsu.com>
Date: Fri, 5 Apr 2024 06:47:18 -0400
Subject: [PATCH v4 1/3] Allow altering of two_phase option of a SUBSCRIPTION

This patch allows user to alter two_phase option of a subscriber provided no uncommitted
prepared transactions are pending on that subscription.

Author: Cherian Ajin, Hayato Kuroda
---
 doc/src/sgml/ref/alter_subscription.sgml      |  6 +-
 src/backend/access/transam/twophase.c         | 43 ++++++++++++
 src/backend/commands/subscriptioncmds.c       | 58 +++++++++++-----
 .../libpqwalreceiver/libpqwalreceiver.c       |  7 +-
 src/backend/replication/logical/launcher.c    | 21 ++++++
 src/backend/replication/logical/worker.c      |  2 +-
 src/backend/replication/slot.c                | 19 +++++-
 src/backend/replication/walsender.c           | 20 ++++--
 src/bin/psql/tab-complete.c                   |  2 +-
 src/include/access/twophase.h                 |  3 +
 src/include/replication/slot.h                |  3 +-
 src/include/replication/walreceiver.h         |  5 +-
 src/include/replication/worker_internal.h     |  1 +
 src/test/regress/expected/subscription.out    |  5 +-
 src/test/regress/sql/subscription.sql         |  5 +-
 src/test/subscription/t/021_twophase.pl       | 67 ++++++++++++++++++-
 16 files changed, 227 insertions(+), 40 deletions(-)

diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index 413ce68ce2..20b45e36e0 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -227,9 +227,11 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-disable-on-error"><literal>disable_on_error</literal></link>,
       <link linkend="sql-createsubscription-params-with-password-required"><literal>password_required</literal></link>,
       <link linkend="sql-createsubscription-params-with-run-as-owner"><literal>run_as_owner</literal></link>,
-      <link linkend="sql-createsubscription-params-with-origin"><literal>origin</literal></link>, and
-      <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>.
+      <link linkend="sql-createsubscription-params-with-origin"><literal>origin</literal></link>,
+      <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>, and
+      <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>.
       Only a superuser can set <literal>password_required = false</literal>.
+      <literal>two_phase</literal> can be altered only for disabled subscription.
      </para>
 
      <para>
diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index 8090ac9fc1..495f99a357 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -2682,3 +2682,46 @@ LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 	LWLockRelease(TwoPhaseStateLock);
 	return found;
 }
+
+/*
+ * checkGid
+ */
+static bool
+checkGid(char *gid, Oid subid)
+{
+	int			ret;
+	Oid			subid_written,
+				xid;
+
+	ret = sscanf(gid, "pg_gid_%u_%u", &subid_written, &xid);
+
+	if (ret != 2 || subid != subid_written)
+		return false;
+
+	return true;
+}
+
+/*
+ * LookupGXactBySubid
+ *		Check if the prepared transaction done by apply worker exists.
+ */
+bool
+LookupGXactBySubid(Oid subid)
+{
+	bool		found = false;
+
+	LWLockAcquire(TwoPhaseStateLock, LW_SHARED);
+	for (int i = 0; i < TwoPhaseState->numPrepXacts; i++)
+	{
+		GlobalTransaction gxact = TwoPhaseState->prepXacts[i];
+
+		/* Ignore not-yet-valid GIDs. */
+		if (gxact->valid && checkGid(gxact->gid, subid))
+		{
+			found = true;
+			break;
+		}
+	}
+	LWLockRelease(TwoPhaseStateLock);
+	return found;
+}
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index 5a47fa984d..3299a60fff 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -16,6 +16,7 @@
 
 #include "access/htup_details.h"
 #include "access/table.h"
+#include "access/twophase.h"
 #include "access/xact.h"
 #include "catalog/catalog.h"
 #include "catalog/dependency.h"
@@ -849,7 +850,7 @@ CreateSubscription(ParseState *pstate, CreateSubscriptionStmt *stmt,
 			else if (opts.slot_name &&
 					 (opts.failover || walrcv_server_version(wrconn) >= 170000))
 			{
-				walrcv_alter_slot(wrconn, opts.slot_name, opts.failover);
+				walrcv_alter_slot(wrconn, opts.slot_name, opts.twophase, opts.failover);
 			}
 		}
 		PG_FINALLY();
@@ -1165,7 +1166,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 			{
 				supported_opts = (SUBOPT_SLOT_NAME |
 								  SUBOPT_SYNCHRONOUS_COMMIT | SUBOPT_BINARY |
-								  SUBOPT_STREAMING | SUBOPT_DISABLE_ON_ERR |
+								  SUBOPT_STREAMING | SUBOPT_TWOPHASE_COMMIT |
+								  SUBOPT_DISABLE_ON_ERR |
 								  SUBOPT_PASSWORD_REQUIRED |
 								  SUBOPT_RUN_AS_OWNER | SUBOPT_FAILOVER |
 								  SUBOPT_ORIGIN);
@@ -1173,6 +1175,41 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 				parse_subscription_options(pstate, stmt->options,
 										   supported_opts, &opts);
 
+				/* XXX */
+				if (IsSet(opts.specified_opts, SUBOPT_TWOPHASE_COMMIT))
+				{
+					/*
+					 * two_phase can be only changed for disabled
+					 * subscriptions
+					 */
+					if (form->subenabled)
+						ereport(ERROR,
+								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+								 errmsg("cannot set %s for enabled subscription",
+										"two_phase")));
+
+					/*
+					 * Stop all the subscription workers, just in case. Workers
+					 * may still survive even if the subscription is disabled.
+					 */
+					logicalrep_workers_stop(subid);
+
+					/* Check whether the number of prepared transactions */
+					if (!opts.twophase &&
+						form->subtwophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
+						LookupGXactBySubid(subid))
+						ereport(ERROR,
+								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+								 errmsg("cannot disable two_phase when uncommitted prepared transactions present")));
+
+					/* Change system catalog acoordingly */
+					values[Anum_pg_subscription_subtwophasestate - 1] =
+						CharGetDatum(opts.twophase ?
+									 LOGICALREP_TWOPHASE_STATE_PENDING :
+									 LOGICALREP_TWOPHASE_STATE_DISABLED);
+					replaces[Anum_pg_subscription_subtwophasestate - 1] = true;
+				}
+
 				if (IsSet(opts.specified_opts, SUBOPT_SLOT_NAME))
 				{
 					/*
@@ -1521,7 +1558,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 	 * doing the database operations we won't be able to rollback altered
 	 * slot.
 	 */
-	if (replaces[Anum_pg_subscription_subfailover - 1])
+	if (replaces[Anum_pg_subscription_subtwophasestate - 1] ||
+		replaces[Anum_pg_subscription_subfailover - 1])
 	{
 		bool		must_use_password;
 		char	   *err;
@@ -1541,7 +1579,7 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 
 		PG_TRY();
 		{
-			walrcv_alter_slot(wrconn, sub->slotname, opts.failover);
+			walrcv_alter_slot(wrconn, sub->slotname, opts.twophase, opts.failover);
 		}
 		PG_FINALLY();
 		{
@@ -1578,7 +1616,6 @@ DropSubscription(DropSubscriptionStmt *stmt, bool isTopLevel)
 	char	   *subname;
 	char	   *conninfo;
 	char	   *slotname;
-	List	   *subworkers;
 	ListCell   *lc;
 	char		originname[NAMEDATALEN];
 	char	   *err = NULL;
@@ -1688,16 +1725,7 @@ DropSubscription(DropSubscriptionStmt *stmt, bool isTopLevel)
 	 * New workers won't be started because we hold an exclusive lock on the
 	 * subscription till the end of the transaction.
 	 */
-	LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
-	subworkers = logicalrep_workers_find(subid, false);
-	LWLockRelease(LogicalRepWorkerLock);
-	foreach(lc, subworkers)
-	{
-		LogicalRepWorker *w = (LogicalRepWorker *) lfirst(lc);
-
-		logicalrep_worker_stop(w->subid, w->relid);
-	}
-	list_free(subworkers);
+	logicalrep_workers_stop(subid);
 
 	/*
 	 * Remove the no-longer-useful entry in the launcher's table of apply
diff --git a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
index 3c2b1bb496..baef3bdec0 100644
--- a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
+++ b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
@@ -80,7 +80,7 @@ static char *libpqrcv_create_slot(WalReceiverConn *conn,
 								  CRSSnapshotAction snapshot_action,
 								  XLogRecPtr *lsn);
 static void libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-								bool failover);
+								bool two_phase, bool failover);
 static pid_t libpqrcv_get_backend_pid(WalReceiverConn *conn);
 static WalRcvExecResult *libpqrcv_exec(WalReceiverConn *conn,
 									   const char *query,
@@ -1121,14 +1121,15 @@ libpqrcv_create_slot(WalReceiverConn *conn, const char *slotname,
  */
 static void
 libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-					bool failover)
+					bool two_phase, bool failover)
 {
 	StringInfoData cmd;
 	PGresult   *res;
 
 	initStringInfo(&cmd);
-	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( FAILOVER %s )",
+	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( TWO_PHASE %s, FAILOVER %s )",
 					 quote_identifier(slotname),
+					 two_phase ? "true" : "false",
 					 failover ? "true" : "false");
 
 	res = libpqrcv_PQexec(conn->streamConn, cmd.data);
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 66070e9131..94b73f3085 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -623,6 +623,27 @@ logicalrep_worker_stop(Oid subid, Oid relid)
 	LWLockRelease(LogicalRepWorkerLock);
 }
 
+/*
+ * Stop all the subscription workers.
+ */
+void
+logicalrep_workers_stop(Oid subid)
+{
+	List	   *subworkers;
+	ListCell   *lc;
+
+	LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
+	subworkers = logicalrep_workers_find(subid, false);
+	LWLockRelease(LogicalRepWorkerLock);
+	foreach(lc, subworkers)
+	{
+		LogicalRepWorker *w = (LogicalRepWorker *) lfirst(lc);
+
+		logicalrep_worker_stop(w->subid, w->relid);
+	}
+	list_free(subworkers);
+}
+
 /*
  * Stop the given logical replication parallel apply worker.
  *
diff --git a/src/backend/replication/logical/worker.c b/src/backend/replication/logical/worker.c
index b5a80fe3e8..374aa22091 100644
--- a/src/backend/replication/logical/worker.c
+++ b/src/backend/replication/logical/worker.c
@@ -3911,7 +3911,7 @@ maybe_reread_subscription(void)
 	/* !slotname should never happen when enabled is true. */
 	Assert(newsub->slotname);
 
-	/* two-phase should not be altered */
+	/* two-phase should not be altered while the worker exists */
 	Assert(newsub->twophasestate == MySubscription->twophasestate);
 
 	/*
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index cebf44bb0f..621f35ab1e 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -800,8 +800,10 @@ ReplicationSlotDrop(const char *name, bool nowait)
  * Change the definition of the slot identified by the specified name.
  */
 void
-ReplicationSlotAlter(const char *name, bool failover)
+ReplicationSlotAlter(const char *name, bool two_phase, bool failover)
 {
+	bool		update_slot = false;
+
 	Assert(MyReplicationSlot == NULL);
 
 	ReplicationSlotAcquire(name, false);
@@ -844,12 +846,27 @@ ReplicationSlotAlter(const char *name, bool failover)
 				errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 				errmsg("cannot enable failover for a temporary replication slot"));
 
+	if (MyReplicationSlot->data.two_phase != two_phase)
+	{
+		SpinLockAcquire(&MyReplicationSlot->mutex);
+		MyReplicationSlot->data.two_phase = two_phase;
+		SpinLockRelease(&MyReplicationSlot->mutex);
+
+		update_slot = true;
+	}
+
+
 	if (MyReplicationSlot->data.failover != failover)
 	{
 		SpinLockAcquire(&MyReplicationSlot->mutex);
 		MyReplicationSlot->data.failover = failover;
 		SpinLockRelease(&MyReplicationSlot->mutex);
 
+		update_slot = true;
+	}
+
+	if (update_slot)
+	{
 		ReplicationSlotMarkDirty();
 		ReplicationSlotSave();
 	}
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index bc40c454de..be155067ce 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1411,14 +1411,25 @@ DropReplicationSlot(DropReplicationSlotCmd *cmd)
  * Process extra options given to ALTER_REPLICATION_SLOT.
  */
 static void
-ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd, bool *failover)
+ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd,
+						  bool *two_phase, bool *failover)
 {
+	bool		two_phase_given = false;
 	bool		failover_given = false;
 
 	/* Parse options */
 	foreach_ptr(DefElem, defel, cmd->options)
 	{
-		if (strcmp(defel->defname, "failover") == 0)
+		if (strcmp(defel->defname, "two_phase") == 0)
+		{
+			if (two_phase_given)
+				ereport(ERROR,
+						(errcode(ERRCODE_SYNTAX_ERROR),
+						 errmsg("conflicting or redundant options")));
+			two_phase_given = true;
+			*two_phase = defGetBoolean(defel);
+		}
+		else if (strcmp(defel->defname, "failover") == 0)
 		{
 			if (failover_given)
 				ereport(ERROR,
@@ -1438,10 +1449,11 @@ ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd, bool *failover)
 static void
 AlterReplicationSlot(AlterReplicationSlotCmd *cmd)
 {
+	bool		two_phase = false;
 	bool		failover = false;
 
-	ParseAlterReplSlotOptions(cmd, &failover);
-	ReplicationSlotAlter(cmd->slotname, failover);
+	ParseAlterReplSlotOptions(cmd, &two_phase, &failover);
+	ReplicationSlotAlter(cmd->slotname, two_phase, failover);
 }
 
 /*
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
index 6fee3160f0..5ff84301cd 100644
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -1948,7 +1948,7 @@ psql_completion(const char *text, int start, int end)
 	else if (HeadMatches("ALTER", "SUBSCRIPTION", MatchAny) && TailMatches("SET", "("))
 		COMPLETE_WITH("binary", "disable_on_error", "failover", "origin",
 					  "password_required", "run_as_owner", "slot_name",
-					  "streaming", "synchronous_commit");
+					  "streaming", "synchronous_commit", "two_phase");
 	/* ALTER SUBSCRIPTION <name> SKIP ( */
 	else if (HeadMatches("ALTER", "SUBSCRIPTION", MatchAny) && TailMatches("SKIP", "("))
 		COMPLETE_WITH("lsn");
diff --git a/src/include/access/twophase.h b/src/include/access/twophase.h
index 56248c0006..d493ed24c5 100644
--- a/src/include/access/twophase.h
+++ b/src/include/access/twophase.h
@@ -62,4 +62,7 @@ extern void PrepareRedoRemove(TransactionId xid, bool giveWarning);
 extern void restoreTwoPhaseData(void);
 extern bool LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 						TimestampTz origin_prepare_timestamp);
+
+extern bool LookupGXactBySubid(Oid subid);
+
 #endif							/* TWOPHASE_H */
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 7b937d1a0c..2fcb11418f 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -243,7 +243,8 @@ extern void ReplicationSlotCreate(const char *name, bool db_specific,
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
 extern void ReplicationSlotDropAcquired(void);
-extern void ReplicationSlotAlter(const char *name, bool failover);
+extern void ReplicationSlotAlter(const char *name, bool two_phase,
+								 bool failover);
 
 extern void ReplicationSlotAcquire(const char *name, bool nowait);
 extern void ReplicationSlotRelease(void);
diff --git a/src/include/replication/walreceiver.h b/src/include/replication/walreceiver.h
index 12f71fa99b..a443f402f5 100644
--- a/src/include/replication/walreceiver.h
+++ b/src/include/replication/walreceiver.h
@@ -377,6 +377,7 @@ typedef char *(*walrcv_create_slot_fn) (WalReceiverConn *conn,
  */
 typedef void (*walrcv_alter_slot_fn) (WalReceiverConn *conn,
 									  const char *slotname,
+									  bool two_phase,
 									  bool failover);
 
 /*
@@ -455,8 +456,8 @@ extern PGDLLIMPORT WalReceiverFunctionsType *WalReceiverFunctions;
 	WalReceiverFunctions->walrcv_send(conn, buffer, nbytes)
 #define walrcv_create_slot(conn, slotname, temporary, two_phase, failover, snapshot_action, lsn) \
 	WalReceiverFunctions->walrcv_create_slot(conn, slotname, temporary, two_phase, failover, snapshot_action, lsn)
-#define walrcv_alter_slot(conn, slotname, failover) \
-	WalReceiverFunctions->walrcv_alter_slot(conn, slotname, failover)
+#define walrcv_alter_slot(conn, slotname, two_phase, failover) \
+	WalReceiverFunctions->walrcv_alter_slot(conn, slotname, two_phase, failover)
 #define walrcv_get_backend_pid(conn) \
 	WalReceiverFunctions->walrcv_get_backend_pid(conn)
 #define walrcv_exec(conn, exec, nRetTypes, retTypes) \
diff --git a/src/include/replication/worker_internal.h b/src/include/replication/worker_internal.h
index 515aefd519..d5428263c1 100644
--- a/src/include/replication/worker_internal.h
+++ b/src/include/replication/worker_internal.h
@@ -246,6 +246,7 @@ extern bool logicalrep_worker_launch(LogicalRepWorkerType wtype,
 									 Oid userid, Oid relid,
 									 dsm_handle subworker_dsm);
 extern void logicalrep_worker_stop(Oid subid, Oid relid);
+extern void logicalrep_workers_stop(Oid subid);
 extern void logicalrep_pa_worker_stop(ParallelApplyWorkerInfo *winfo);
 extern void logicalrep_worker_wakeup(Oid subid, Oid relid);
 extern void logicalrep_worker_wakeup_ptr(LogicalRepWorker *worker);
diff --git a/src/test/regress/expected/subscription.out b/src/test/regress/expected/subscription.out
index 1eee6b17b8..9bba656e00 100644
--- a/src/test/regress/expected/subscription.out
+++ b/src/test/regress/expected/subscription.out
@@ -379,10 +379,7 @@ HINT:  To initiate replication, you must manually create the replication slot, e
  regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | p                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
---fail - alter of two_phase option not supported.
-ALTER SUBSCRIPTION regress_testsub SET (two_phase = false);
-ERROR:  unrecognized subscription parameter: "two_phase"
--- but can alter streaming when two_phase enabled
+-- We can alter streaming when two_phase enabled
 ALTER SUBSCRIPTION regress_testsub SET (streaming = true);
 \dRs+
                                                                                                                 List of subscriptions
diff --git a/src/test/regress/sql/subscription.sql b/src/test/regress/sql/subscription.sql
index 1b2a23ba7b..9ff151f806 100644
--- a/src/test/regress/sql/subscription.sql
+++ b/src/test/regress/sql/subscription.sql
@@ -257,10 +257,7 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUBLICATION testpub WITH (connect = false, two_phase = true);
 
 \dRs+
---fail - alter of two_phase option not supported.
-ALTER SUBSCRIPTION regress_testsub SET (two_phase = false);
-
--- but can alter streaming when two_phase enabled
+-- We can alter streaming when two_phase enabled
 ALTER SUBSCRIPTION regress_testsub SET (streaming = true);
 
 \dRs+
diff --git a/src/test/subscription/t/021_twophase.pl b/src/test/subscription/t/021_twophase.pl
index 9437cd4c3b..e710f3c4c0 100644
--- a/src/test/subscription/t/021_twophase.pl
+++ b/src/test/subscription/t/021_twophase.pl
@@ -367,6 +367,71 @@ $result =
   $node_subscriber->safe_psql('postgres', "SELECT count(*) FROM tab_copy;");
 is($result, qq(2), 'replicated data in subscriber table');
 
+# Disable the subscription and alter it to two_phase = false,
+# verify that the altered subscription reflects the two_phase option.
+
+# Alter subscription two_phase to false
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy DISABLE");
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = false)");
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy ENABLE");
+
+# Wait for subscription startup
+$node_subscriber->wait_for_subscription_sync($node_publisher, $appname_copy);
+
+# Make sure that the two-phase is disabled on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+       "SELECT subtwophasestate FROM pg_subscription WHERE subname = 'tap_sub_copy';"
+);
+is($result, qq(d), 'two-phase is disabled');
+
+# Now do a prepare on publisher and make sure that it is not replicated.
+$node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub");
+$node_publisher->safe_psql(
+       'postgres', qq{
+    BEGIN;
+    INSERT INTO tab_copy VALUES (100);
+    PREPARE TRANSACTION 'newgid';
+	});
+
+# Wait for the subscriber to catchup
+$node_publisher->wait_for_catchup($appname_copy);
+
+# Make sure that there is 0 prepared transaction on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT count(*) FROM pg_prepared_xacts;");
+is($result, qq(0), 'transaction is prepared on subscriber');
+
+# Now commit the insert and verify that it IS replicated
+$node_publisher->safe_psql('postgres', "COMMIT PREPARED 'newgid';");
+
+# Wait for the subscriber to catchup
+$node_publisher->wait_for_catchup($appname_copy);
+
+# Made sure that the commited transaction is replicated.
+$result =
+	$node_subscriber->safe_psql('postgres', "SELECT count(*) FROM tab_copy;");
+is($result, qq(3), 'replicated data in subscriber table');
+
+# Alter subscription two_phase to true
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy DISABLE");
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = true)");
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy ENABLE");
+
+# Wait for subscription startup
+$node_subscriber->wait_for_subscription_sync($node_publisher, $appname_copy);
+
+# Make sure that the two-phase is enabled on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT subtwophasestate FROM pg_subscription WHERE subname = 'tap_sub_copy';"
+);
+is($result, qq(e), 'two-phase is disabled');
+
 $node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub_copy;");
 $node_publisher->safe_psql('postgres', "DROP PUBLICATION tap_pub_copy;");
 
@@ -374,8 +439,6 @@ $node_publisher->safe_psql('postgres', "DROP PUBLICATION tap_pub_copy;");
 # check all the cleanup
 ###############################
 
-$node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub");
-
 $result = $node_subscriber->safe_psql('postgres',
 	"SELECT count(*) FROM pg_subscription");
 is($result, qq(0), 'check subscription was dropped on subscriber');
-- 
2.43.0

From 43a5314acbbfdf8210f83c03576cfbcc2faddb80 Mon Sep 17 00:00:00 2001
From: Ajin Cherian <ajinc@fast.au.fujitsu.com>
Date: Fri, 5 Apr 2024 06:47:18 -0400
Subject: [PATCH v5 1/4] Allow altering of two_phase option of a SUBSCRIPTION

This patch allows user to alter two_phase option of a subscriber provided no uncommitted
prepared transactions are pending on that subscription.

Author: Cherian Ajin, Hayato Kuroda
---
 doc/src/sgml/ref/alter_subscription.sgml      |  6 +-
 src/backend/access/transam/twophase.c         | 43 ++++++++++++
 src/backend/commands/subscriptioncmds.c       | 58 +++++++++++-----
 .../libpqwalreceiver/libpqwalreceiver.c       |  7 +-
 src/backend/replication/logical/launcher.c    | 21 ++++++
 src/backend/replication/logical/worker.c      |  2 +-
 src/backend/replication/slot.c                | 19 +++++-
 src/backend/replication/walsender.c           | 20 ++++--
 src/bin/psql/tab-complete.c                   |  2 +-
 src/include/access/twophase.h                 |  3 +
 src/include/replication/slot.h                |  3 +-
 src/include/replication/walreceiver.h         |  5 +-
 src/include/replication/worker_internal.h     |  1 +
 src/test/regress/expected/subscription.out    |  5 +-
 src/test/regress/sql/subscription.sql         |  5 +-
 src/test/subscription/t/021_twophase.pl       | 67 ++++++++++++++++++-
 16 files changed, 227 insertions(+), 40 deletions(-)

diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index 413ce68ce2..20b45e36e0 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -227,9 +227,11 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-disable-on-error"><literal>disable_on_error</literal></link>,
       <link linkend="sql-createsubscription-params-with-password-required"><literal>password_required</literal></link>,
       <link linkend="sql-createsubscription-params-with-run-as-owner"><literal>run_as_owner</literal></link>,
-      <link linkend="sql-createsubscription-params-with-origin"><literal>origin</literal></link>, and
-      <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>.
+      <link linkend="sql-createsubscription-params-with-origin"><literal>origin</literal></link>,
+      <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>, and
+      <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>.
       Only a superuser can set <literal>password_required = false</literal>.
+      <literal>two_phase</literal> can be altered only for disabled subscription.
      </para>
 
      <para>
diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index 8090ac9fc1..495f99a357 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -2682,3 +2682,46 @@ LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 	LWLockRelease(TwoPhaseStateLock);
 	return found;
 }
+
+/*
+ * checkGid
+ */
+static bool
+checkGid(char *gid, Oid subid)
+{
+	int			ret;
+	Oid			subid_written,
+				xid;
+
+	ret = sscanf(gid, "pg_gid_%u_%u", &subid_written, &xid);
+
+	if (ret != 2 || subid != subid_written)
+		return false;
+
+	return true;
+}
+
+/*
+ * LookupGXactBySubid
+ *		Check if the prepared transaction done by apply worker exists.
+ */
+bool
+LookupGXactBySubid(Oid subid)
+{
+	bool		found = false;
+
+	LWLockAcquire(TwoPhaseStateLock, LW_SHARED);
+	for (int i = 0; i < TwoPhaseState->numPrepXacts; i++)
+	{
+		GlobalTransaction gxact = TwoPhaseState->prepXacts[i];
+
+		/* Ignore not-yet-valid GIDs. */
+		if (gxact->valid && checkGid(gxact->gid, subid))
+		{
+			found = true;
+			break;
+		}
+	}
+	LWLockRelease(TwoPhaseStateLock);
+	return found;
+}
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index 5a47fa984d..3299a60fff 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -16,6 +16,7 @@
 
 #include "access/htup_details.h"
 #include "access/table.h"
+#include "access/twophase.h"
 #include "access/xact.h"
 #include "catalog/catalog.h"
 #include "catalog/dependency.h"
@@ -849,7 +850,7 @@ CreateSubscription(ParseState *pstate, CreateSubscriptionStmt *stmt,
 			else if (opts.slot_name &&
 					 (opts.failover || walrcv_server_version(wrconn) >= 170000))
 			{
-				walrcv_alter_slot(wrconn, opts.slot_name, opts.failover);
+				walrcv_alter_slot(wrconn, opts.slot_name, opts.twophase, opts.failover);
 			}
 		}
 		PG_FINALLY();
@@ -1165,7 +1166,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 			{
 				supported_opts = (SUBOPT_SLOT_NAME |
 								  SUBOPT_SYNCHRONOUS_COMMIT | SUBOPT_BINARY |
-								  SUBOPT_STREAMING | SUBOPT_DISABLE_ON_ERR |
+								  SUBOPT_STREAMING | SUBOPT_TWOPHASE_COMMIT |
+								  SUBOPT_DISABLE_ON_ERR |
 								  SUBOPT_PASSWORD_REQUIRED |
 								  SUBOPT_RUN_AS_OWNER | SUBOPT_FAILOVER |
 								  SUBOPT_ORIGIN);
@@ -1173,6 +1175,41 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 				parse_subscription_options(pstate, stmt->options,
 										   supported_opts, &opts);
 
+				/* XXX */
+				if (IsSet(opts.specified_opts, SUBOPT_TWOPHASE_COMMIT))
+				{
+					/*
+					 * two_phase can be only changed for disabled
+					 * subscriptions
+					 */
+					if (form->subenabled)
+						ereport(ERROR,
+								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+								 errmsg("cannot set %s for enabled subscription",
+										"two_phase")));
+
+					/*
+					 * Stop all the subscription workers, just in case. Workers
+					 * may still survive even if the subscription is disabled.
+					 */
+					logicalrep_workers_stop(subid);
+
+					/* Check whether the number of prepared transactions */
+					if (!opts.twophase &&
+						form->subtwophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
+						LookupGXactBySubid(subid))
+						ereport(ERROR,
+								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+								 errmsg("cannot disable two_phase when uncommitted prepared transactions present")));
+
+					/* Change system catalog acoordingly */
+					values[Anum_pg_subscription_subtwophasestate - 1] =
+						CharGetDatum(opts.twophase ?
+									 LOGICALREP_TWOPHASE_STATE_PENDING :
+									 LOGICALREP_TWOPHASE_STATE_DISABLED);
+					replaces[Anum_pg_subscription_subtwophasestate - 1] = true;
+				}
+
 				if (IsSet(opts.specified_opts, SUBOPT_SLOT_NAME))
 				{
 					/*
@@ -1521,7 +1558,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 	 * doing the database operations we won't be able to rollback altered
 	 * slot.
 	 */
-	if (replaces[Anum_pg_subscription_subfailover - 1])
+	if (replaces[Anum_pg_subscription_subtwophasestate - 1] ||
+		replaces[Anum_pg_subscription_subfailover - 1])
 	{
 		bool		must_use_password;
 		char	   *err;
@@ -1541,7 +1579,7 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 
 		PG_TRY();
 		{
-			walrcv_alter_slot(wrconn, sub->slotname, opts.failover);
+			walrcv_alter_slot(wrconn, sub->slotname, opts.twophase, opts.failover);
 		}
 		PG_FINALLY();
 		{
@@ -1578,7 +1616,6 @@ DropSubscription(DropSubscriptionStmt *stmt, bool isTopLevel)
 	char	   *subname;
 	char	   *conninfo;
 	char	   *slotname;
-	List	   *subworkers;
 	ListCell   *lc;
 	char		originname[NAMEDATALEN];
 	char	   *err = NULL;
@@ -1688,16 +1725,7 @@ DropSubscription(DropSubscriptionStmt *stmt, bool isTopLevel)
 	 * New workers won't be started because we hold an exclusive lock on the
 	 * subscription till the end of the transaction.
 	 */
-	LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
-	subworkers = logicalrep_workers_find(subid, false);
-	LWLockRelease(LogicalRepWorkerLock);
-	foreach(lc, subworkers)
-	{
-		LogicalRepWorker *w = (LogicalRepWorker *) lfirst(lc);
-
-		logicalrep_worker_stop(w->subid, w->relid);
-	}
-	list_free(subworkers);
+	logicalrep_workers_stop(subid);
 
 	/*
 	 * Remove the no-longer-useful entry in the launcher's table of apply
diff --git a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
index 3c2b1bb496..baef3bdec0 100644
--- a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
+++ b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
@@ -80,7 +80,7 @@ static char *libpqrcv_create_slot(WalReceiverConn *conn,
 								  CRSSnapshotAction snapshot_action,
 								  XLogRecPtr *lsn);
 static void libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-								bool failover);
+								bool two_phase, bool failover);
 static pid_t libpqrcv_get_backend_pid(WalReceiverConn *conn);
 static WalRcvExecResult *libpqrcv_exec(WalReceiverConn *conn,
 									   const char *query,
@@ -1121,14 +1121,15 @@ libpqrcv_create_slot(WalReceiverConn *conn, const char *slotname,
  */
 static void
 libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-					bool failover)
+					bool two_phase, bool failover)
 {
 	StringInfoData cmd;
 	PGresult   *res;
 
 	initStringInfo(&cmd);
-	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( FAILOVER %s )",
+	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( TWO_PHASE %s, FAILOVER %s )",
 					 quote_identifier(slotname),
+					 two_phase ? "true" : "false",
 					 failover ? "true" : "false");
 
 	res = libpqrcv_PQexec(conn->streamConn, cmd.data);
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 66070e9131..94b73f3085 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -623,6 +623,27 @@ logicalrep_worker_stop(Oid subid, Oid relid)
 	LWLockRelease(LogicalRepWorkerLock);
 }
 
+/*
+ * Stop all the subscription workers.
+ */
+void
+logicalrep_workers_stop(Oid subid)
+{
+	List	   *subworkers;
+	ListCell   *lc;
+
+	LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
+	subworkers = logicalrep_workers_find(subid, false);
+	LWLockRelease(LogicalRepWorkerLock);
+	foreach(lc, subworkers)
+	{
+		LogicalRepWorker *w = (LogicalRepWorker *) lfirst(lc);
+
+		logicalrep_worker_stop(w->subid, w->relid);
+	}
+	list_free(subworkers);
+}
+
 /*
  * Stop the given logical replication parallel apply worker.
  *
diff --git a/src/backend/replication/logical/worker.c b/src/backend/replication/logical/worker.c
index b5a80fe3e8..374aa22091 100644
--- a/src/backend/replication/logical/worker.c
+++ b/src/backend/replication/logical/worker.c
@@ -3911,7 +3911,7 @@ maybe_reread_subscription(void)
 	/* !slotname should never happen when enabled is true. */
 	Assert(newsub->slotname);
 
-	/* two-phase should not be altered */
+	/* two-phase should not be altered while the worker exists */
 	Assert(newsub->twophasestate == MySubscription->twophasestate);
 
 	/*
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index cebf44bb0f..621f35ab1e 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -800,8 +800,10 @@ ReplicationSlotDrop(const char *name, bool nowait)
  * Change the definition of the slot identified by the specified name.
  */
 void
-ReplicationSlotAlter(const char *name, bool failover)
+ReplicationSlotAlter(const char *name, bool two_phase, bool failover)
 {
+	bool		update_slot = false;
+
 	Assert(MyReplicationSlot == NULL);
 
 	ReplicationSlotAcquire(name, false);
@@ -844,12 +846,27 @@ ReplicationSlotAlter(const char *name, bool failover)
 				errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 				errmsg("cannot enable failover for a temporary replication slot"));
 
+	if (MyReplicationSlot->data.two_phase != two_phase)
+	{
+		SpinLockAcquire(&MyReplicationSlot->mutex);
+		MyReplicationSlot->data.two_phase = two_phase;
+		SpinLockRelease(&MyReplicationSlot->mutex);
+
+		update_slot = true;
+	}
+
+
 	if (MyReplicationSlot->data.failover != failover)
 	{
 		SpinLockAcquire(&MyReplicationSlot->mutex);
 		MyReplicationSlot->data.failover = failover;
 		SpinLockRelease(&MyReplicationSlot->mutex);
 
+		update_slot = true;
+	}
+
+	if (update_slot)
+	{
 		ReplicationSlotMarkDirty();
 		ReplicationSlotSave();
 	}
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 9bf7c67f37..c45881554b 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1411,14 +1411,25 @@ DropReplicationSlot(DropReplicationSlotCmd *cmd)
  * Process extra options given to ALTER_REPLICATION_SLOT.
  */
 static void
-ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd, bool *failover)
+ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd,
+						  bool *two_phase, bool *failover)
 {
+	bool		two_phase_given = false;
 	bool		failover_given = false;
 
 	/* Parse options */
 	foreach_ptr(DefElem, defel, cmd->options)
 	{
-		if (strcmp(defel->defname, "failover") == 0)
+		if (strcmp(defel->defname, "two_phase") == 0)
+		{
+			if (two_phase_given)
+				ereport(ERROR,
+						(errcode(ERRCODE_SYNTAX_ERROR),
+						 errmsg("conflicting or redundant options")));
+			two_phase_given = true;
+			*two_phase = defGetBoolean(defel);
+		}
+		else if (strcmp(defel->defname, "failover") == 0)
 		{
 			if (failover_given)
 				ereport(ERROR,
@@ -1438,10 +1449,11 @@ ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd, bool *failover)
 static void
 AlterReplicationSlot(AlterReplicationSlotCmd *cmd)
 {
+	bool		two_phase = false;
 	bool		failover = false;
 
-	ParseAlterReplSlotOptions(cmd, &failover);
-	ReplicationSlotAlter(cmd->slotname, failover);
+	ParseAlterReplSlotOptions(cmd, &two_phase, &failover);
+	ReplicationSlotAlter(cmd->slotname, two_phase, failover);
 }
 
 /*
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
index 6fee3160f0..5ff84301cd 100644
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -1948,7 +1948,7 @@ psql_completion(const char *text, int start, int end)
 	else if (HeadMatches("ALTER", "SUBSCRIPTION", MatchAny) && TailMatches("SET", "("))
 		COMPLETE_WITH("binary", "disable_on_error", "failover", "origin",
 					  "password_required", "run_as_owner", "slot_name",
-					  "streaming", "synchronous_commit");
+					  "streaming", "synchronous_commit", "two_phase");
 	/* ALTER SUBSCRIPTION <name> SKIP ( */
 	else if (HeadMatches("ALTER", "SUBSCRIPTION", MatchAny) && TailMatches("SKIP", "("))
 		COMPLETE_WITH("lsn");
diff --git a/src/include/access/twophase.h b/src/include/access/twophase.h
index 56248c0006..d493ed24c5 100644
--- a/src/include/access/twophase.h
+++ b/src/include/access/twophase.h
@@ -62,4 +62,7 @@ extern void PrepareRedoRemove(TransactionId xid, bool giveWarning);
 extern void restoreTwoPhaseData(void);
 extern bool LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 						TimestampTz origin_prepare_timestamp);
+
+extern bool LookupGXactBySubid(Oid subid);
+
 #endif							/* TWOPHASE_H */
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 7b937d1a0c..2fcb11418f 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -243,7 +243,8 @@ extern void ReplicationSlotCreate(const char *name, bool db_specific,
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
 extern void ReplicationSlotDropAcquired(void);
-extern void ReplicationSlotAlter(const char *name, bool failover);
+extern void ReplicationSlotAlter(const char *name, bool two_phase,
+								 bool failover);
 
 extern void ReplicationSlotAcquire(const char *name, bool nowait);
 extern void ReplicationSlotRelease(void);
diff --git a/src/include/replication/walreceiver.h b/src/include/replication/walreceiver.h
index 12f71fa99b..a443f402f5 100644
--- a/src/include/replication/walreceiver.h
+++ b/src/include/replication/walreceiver.h
@@ -377,6 +377,7 @@ typedef char *(*walrcv_create_slot_fn) (WalReceiverConn *conn,
  */
 typedef void (*walrcv_alter_slot_fn) (WalReceiverConn *conn,
 									  const char *slotname,
+									  bool two_phase,
 									  bool failover);
 
 /*
@@ -455,8 +456,8 @@ extern PGDLLIMPORT WalReceiverFunctionsType *WalReceiverFunctions;
 	WalReceiverFunctions->walrcv_send(conn, buffer, nbytes)
 #define walrcv_create_slot(conn, slotname, temporary, two_phase, failover, snapshot_action, lsn) \
 	WalReceiverFunctions->walrcv_create_slot(conn, slotname, temporary, two_phase, failover, snapshot_action, lsn)
-#define walrcv_alter_slot(conn, slotname, failover) \
-	WalReceiverFunctions->walrcv_alter_slot(conn, slotname, failover)
+#define walrcv_alter_slot(conn, slotname, two_phase, failover) \
+	WalReceiverFunctions->walrcv_alter_slot(conn, slotname, two_phase, failover)
 #define walrcv_get_backend_pid(conn) \
 	WalReceiverFunctions->walrcv_get_backend_pid(conn)
 #define walrcv_exec(conn, exec, nRetTypes, retTypes) \
diff --git a/src/include/replication/worker_internal.h b/src/include/replication/worker_internal.h
index 515aefd519..d5428263c1 100644
--- a/src/include/replication/worker_internal.h
+++ b/src/include/replication/worker_internal.h
@@ -246,6 +246,7 @@ extern bool logicalrep_worker_launch(LogicalRepWorkerType wtype,
 									 Oid userid, Oid relid,
 									 dsm_handle subworker_dsm);
 extern void logicalrep_worker_stop(Oid subid, Oid relid);
+extern void logicalrep_workers_stop(Oid subid);
 extern void logicalrep_pa_worker_stop(ParallelApplyWorkerInfo *winfo);
 extern void logicalrep_worker_wakeup(Oid subid, Oid relid);
 extern void logicalrep_worker_wakeup_ptr(LogicalRepWorker *worker);
diff --git a/src/test/regress/expected/subscription.out b/src/test/regress/expected/subscription.out
index 1eee6b17b8..9bba656e00 100644
--- a/src/test/regress/expected/subscription.out
+++ b/src/test/regress/expected/subscription.out
@@ -379,10 +379,7 @@ HINT:  To initiate replication, you must manually create the replication slot, e
  regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | p                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
---fail - alter of two_phase option not supported.
-ALTER SUBSCRIPTION regress_testsub SET (two_phase = false);
-ERROR:  unrecognized subscription parameter: "two_phase"
--- but can alter streaming when two_phase enabled
+-- We can alter streaming when two_phase enabled
 ALTER SUBSCRIPTION regress_testsub SET (streaming = true);
 \dRs+
                                                                                                                 List of subscriptions
diff --git a/src/test/regress/sql/subscription.sql b/src/test/regress/sql/subscription.sql
index 1b2a23ba7b..9ff151f806 100644
--- a/src/test/regress/sql/subscription.sql
+++ b/src/test/regress/sql/subscription.sql
@@ -257,10 +257,7 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUBLICATION testpub WITH (connect = false, two_phase = true);
 
 \dRs+
---fail - alter of two_phase option not supported.
-ALTER SUBSCRIPTION regress_testsub SET (two_phase = false);
-
--- but can alter streaming when two_phase enabled
+-- We can alter streaming when two_phase enabled
 ALTER SUBSCRIPTION regress_testsub SET (streaming = true);
 
 \dRs+
diff --git a/src/test/subscription/t/021_twophase.pl b/src/test/subscription/t/021_twophase.pl
index 9437cd4c3b..e710f3c4c0 100644
--- a/src/test/subscription/t/021_twophase.pl
+++ b/src/test/subscription/t/021_twophase.pl
@@ -367,6 +367,71 @@ $result =
   $node_subscriber->safe_psql('postgres', "SELECT count(*) FROM tab_copy;");
 is($result, qq(2), 'replicated data in subscriber table');
 
+# Disable the subscription and alter it to two_phase = false,
+# verify that the altered subscription reflects the two_phase option.
+
+# Alter subscription two_phase to false
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy DISABLE");
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = false)");
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy ENABLE");
+
+# Wait for subscription startup
+$node_subscriber->wait_for_subscription_sync($node_publisher, $appname_copy);
+
+# Make sure that the two-phase is disabled on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+       "SELECT subtwophasestate FROM pg_subscription WHERE subname = 'tap_sub_copy';"
+);
+is($result, qq(d), 'two-phase is disabled');
+
+# Now do a prepare on publisher and make sure that it is not replicated.
+$node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub");
+$node_publisher->safe_psql(
+       'postgres', qq{
+    BEGIN;
+    INSERT INTO tab_copy VALUES (100);
+    PREPARE TRANSACTION 'newgid';
+	});
+
+# Wait for the subscriber to catchup
+$node_publisher->wait_for_catchup($appname_copy);
+
+# Make sure that there is 0 prepared transaction on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT count(*) FROM pg_prepared_xacts;");
+is($result, qq(0), 'transaction is prepared on subscriber');
+
+# Now commit the insert and verify that it IS replicated
+$node_publisher->safe_psql('postgres', "COMMIT PREPARED 'newgid';");
+
+# Wait for the subscriber to catchup
+$node_publisher->wait_for_catchup($appname_copy);
+
+# Made sure that the commited transaction is replicated.
+$result =
+	$node_subscriber->safe_psql('postgres', "SELECT count(*) FROM tab_copy;");
+is($result, qq(3), 'replicated data in subscriber table');
+
+# Alter subscription two_phase to true
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy DISABLE");
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = true)");
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy ENABLE");
+
+# Wait for subscription startup
+$node_subscriber->wait_for_subscription_sync($node_publisher, $appname_copy);
+
+# Make sure that the two-phase is enabled on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT subtwophasestate FROM pg_subscription WHERE subname = 'tap_sub_copy';"
+);
+is($result, qq(e), 'two-phase is disabled');
+
 $node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub_copy;");
 $node_publisher->safe_psql('postgres', "DROP PUBLICATION tap_pub_copy;");
 
@@ -374,8 +439,6 @@ $node_publisher->safe_psql('postgres', "DROP PUBLICATION tap_pub_copy;");
 # check all the cleanup
 ###############################
 
-$node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub");
-
 $result = $node_subscriber->safe_psql('postgres',
 	"SELECT count(*) FROM pg_subscription");
 is($result, qq(0), 'check subscription was dropped on subscriber');
-- 
2.43.0

From 5db0fa5a9f6d7522ec65fb0acacfa630b02bb63c Mon Sep 17 00:00:00 2001
From: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Date: Wed, 17 Apr 2024 06:18:23 +0000
Subject: [PATCH v5 2/4] Alter slot option two_phase only when altering true to
 false

---
 src/backend/commands/subscriptioncmds.c       | 21 +++++-
 .../libpqwalreceiver/libpqwalreceiver.c       | 21 ++++--
 src/include/replication/walreceiver.h         |  8 +--
 src/test/subscription/meson.build             |  1 +
 src/test/subscription/t/099_twophase_added.pl | 72 +++++++++++++++++++
 5 files changed, 111 insertions(+), 12 deletions(-)
 create mode 100644 src/test/subscription/t/099_twophase_added.pl

diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index 3299a60fff..0d80d6e110 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -850,7 +850,7 @@ CreateSubscription(ParseState *pstate, CreateSubscriptionStmt *stmt,
 			else if (opts.slot_name &&
 					 (opts.failover || walrcv_server_version(wrconn) >= 170000))
 			{
-				walrcv_alter_slot(wrconn, opts.slot_name, opts.twophase, opts.failover);
+				walrcv_alter_slot(wrconn, opts.slot_name, NULL, &opts.failover);
 			}
 		}
 		PG_FINALLY();
@@ -1564,6 +1564,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 		bool		must_use_password;
 		char	   *err;
 		WalReceiverConn *wrconn;
+		bool		two_phase_needs_to_be_updated;
+		bool		failover_needs_to_be_updated;
 
 		/* Load the library providing us libpq calls. */
 		load_file("libpqwalreceiver", false);
@@ -1577,9 +1579,24 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 					(errcode(ERRCODE_CONNECTION_FAILURE),
 					 errmsg("could not connect to the publisher: %s", err)));
 
+		/*
+		 * Consider which slot option must be altered.
+		 *
+		 * We must alter the failover option whenever subfailover is updated.
+		 * Two_phase, however, is altered only when changing true to false.
+		 */
+		two_phase_needs_to_be_updated =
+						(replaces[Anum_pg_subscription_subtwophasestate - 1] &&
+						 !opts.twophase);
+		failover_needs_to_be_updated =
+								replaces[Anum_pg_subscription_subfailover - 1];
+
 		PG_TRY();
 		{
-			walrcv_alter_slot(wrconn, sub->slotname, opts.twophase, opts.failover);
+			if (two_phase_needs_to_be_updated || failover_needs_to_be_updated)
+				walrcv_alter_slot(wrconn, sub->slotname,
+								  two_phase_needs_to_be_updated ? &opts.twophase : NULL,
+								  failover_needs_to_be_updated ? &opts.failover : NULL);
 		}
 		PG_FINALLY();
 		{
diff --git a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
index baef3bdec0..546b599848 100644
--- a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
+++ b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
@@ -80,7 +80,7 @@ static char *libpqrcv_create_slot(WalReceiverConn *conn,
 								  CRSSnapshotAction snapshot_action,
 								  XLogRecPtr *lsn);
 static void libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-								bool two_phase, bool failover);
+								const bool *two_phase, const bool *failover);
 static pid_t libpqrcv_get_backend_pid(WalReceiverConn *conn);
 static WalRcvExecResult *libpqrcv_exec(WalReceiverConn *conn,
 									   const char *query,
@@ -1121,16 +1121,25 @@ libpqrcv_create_slot(WalReceiverConn *conn, const char *slotname,
  */
 static void
 libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-					bool two_phase, bool failover)
+					const bool *two_phase, const bool *failover)
 {
 	StringInfoData cmd;
 	PGresult   *res;
 
 	initStringInfo(&cmd);
-	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( TWO_PHASE %s, FAILOVER %s )",
-					 quote_identifier(slotname),
-					 two_phase ? "true" : "false",
-					 failover ? "true" : "false");
+	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( ",
+					 quote_identifier(slotname));
+
+	if (two_phase)
+		appendStringInfo(&cmd, "TWO_PHASE %s%s ",
+						 (*two_phase) ? "true" : "false",
+						 failover ? ", " : "");
+
+	if (failover)
+		appendStringInfo(&cmd, "FAILOVER %s ",
+						 (*failover) ? "true" : "false");
+
+	appendStringInfoString(&cmd, ");");
 
 	res = libpqrcv_PQexec(conn->streamConn, cmd.data);
 	pfree(cmd.data);
diff --git a/src/include/replication/walreceiver.h b/src/include/replication/walreceiver.h
index a443f402f5..f30637aa4a 100644
--- a/src/include/replication/walreceiver.h
+++ b/src/include/replication/walreceiver.h
@@ -372,13 +372,13 @@ typedef char *(*walrcv_create_slot_fn) (WalReceiverConn *conn,
 /*
  * walrcv_alter_slot_fn
  *
- * Change the definition of a replication slot. Currently, it only supports
- * changing the failover property of the slot.
+ * Change the definition of a replication slot. Currently, it supports
+ * changing the two_phase and the failover property of the slot.
  */
 typedef void (*walrcv_alter_slot_fn) (WalReceiverConn *conn,
 									  const char *slotname,
-									  bool two_phase,
-									  bool failover);
+									  const bool *two_phase,
+									  const bool *failover);
 
 /*
  * walrcv_get_backend_pid_fn
diff --git a/src/test/subscription/meson.build b/src/test/subscription/meson.build
index c591cd7d61..b4bd522c3d 100644
--- a/src/test/subscription/meson.build
+++ b/src/test/subscription/meson.build
@@ -40,6 +40,7 @@ tests += {
       't/031_column_list.pl',
       't/032_subscribe_use_index.pl',
       't/033_run_as_table_owner.pl',
+      't/099_twophase_added.pl',
       't/100_bugs.pl',
     ],
   },
diff --git a/src/test/subscription/t/099_twophase_added.pl b/src/test/subscription/t/099_twophase_added.pl
new file mode 100644
index 0000000000..c13a37675a
--- /dev/null
+++ b/src/test/subscription/t/099_twophase_added.pl
@@ -0,0 +1,72 @@
+# Copyright (c) 2021-2024, PostgreSQL Global Development Group
+
+# Additional tests for altering two_phase option
+use strict;
+use warnings FATAL => 'all';
+use PostgreSQL::Test::Cluster;
+use PostgreSQL::Test::Utils;
+use Test::More;
+
+# Initialize publisher node
+my $node_publisher = PostgreSQL::Test::Cluster->new('publisher');
+$node_publisher->init(allows_streaming => 'logical');
+$node_publisher->append_conf('postgresql.conf',
+	qq(max_prepared_transactions = 10));
+$node_publisher->start;
+
+# Create subscriber node
+my $node_subscriber = PostgreSQL::Test::Cluster->new('subscriber');
+$node_subscriber->init;
+$node_subscriber->append_conf('postgresql.conf',
+	qq(max_prepared_transactions = 10));
+$node_subscriber->start;
+
+# Define pre-existing tables on both nodes
+$node_publisher->safe_psql('postgres',
+    "CREATE TABLE tab_full (a int PRIMARY KEY);");
+$node_subscriber->safe_psql('postgres',
+	"CREATE TABLE tab_full (a int PRIMARY KEY)");
+
+# Setup logical replication, with two_phase = off
+my $publisher_connstr = $node_publisher->connstr . ' dbname=postgres';
+$node_publisher->safe_psql('postgres',
+	"CREATE PUBLICATION pub FOR ALL TABLES");
+
+$node_subscriber->safe_psql(
+	'postgres', "
+	CREATE SUBSCRIPTION sub
+	CONNECTION '$publisher_connstr' PUBLICATION pub
+	WITH (two_phase = off, copy_data = off)");
+
+######
+# Check the case that prepared transactions exist on publisher node
+######
+
+$node_publisher->safe_psql(
+	'postgres', "
+	BEGIN;
+	INSERT INTO tab_full VALUES (generate_series(1, 5));
+	PREPARE TRANSACTION 'test_prepared_tab_full';");
+
+$node_publisher->wait_for_catchup('sub');
+
+my $result = $node_subscriber->safe_psql('postgres',
+    "SELECT count(*) FROM pg_prepared_xacts;");
+is($result, q(0), "transaction is not prepared on subscriber");
+
+$node_subscriber->safe_psql(
+    'postgres', "
+    ALTER SUBSCRIPTION sub DISABLE;
+    ALTER SUBSCRIPTION sub SET (two_phase = on);
+    ALTER SUBSCRIPTION sub ENABLE;");
+
+$node_publisher->safe_psql( 'postgres',
+    "COMMIT PREPARED 'test_prepared_tab_full';");
+$node_publisher->wait_for_catchup('sub');
+
+$result = $node_subscriber->safe_psql('postgres',
+    "SELECT count(*) FROM tab_full;");
+is($result, q(5),
+   "prepared transactions done before altering can be replicated");
+
+done_testing();
-- 
2.43.0

From bf47ee629d262dae465b3113e946baf6dca9b592 Mon Sep 17 00:00:00 2001
From: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Date: Mon, 8 Apr 2024 12:39:12 +0000
Subject: [PATCH v5 3/4] Abort prepared transactions while altering two_phase
 to false

---
 doc/src/sgml/ref/alter_subscription.sgml      | 10 +++++-
 src/backend/access/transam/twophase.c         | 19 +++++-----
 src/backend/commands/subscriptioncmds.c       | 27 +++++++++++---
 src/include/access/twophase.h                 |  3 +-
 src/test/subscription/t/099_twophase_added.pl | 35 +++++++++++++++++++
 5 files changed, 77 insertions(+), 17 deletions(-)

diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index 20b45e36e0..cfd2a18e2c 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -231,7 +231,6 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>, and
       <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>.
       Only a superuser can set <literal>password_required = false</literal>.
-      <literal>two_phase</literal> can be altered only for disabled subscription.
      </para>
 
      <para>
@@ -253,6 +252,15 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>
       option is enabled.
      </para>
+
+     <para>
+      <literal>two_phase</literal> can be altered only for disabled
+      subscriptions. When altering the parameter from <literal>true</literal>
+      to <literal>false</literal>,  the backend process checks prepared
+      transactions done by the logical replication worker and aborts them. If
+      prepared transactions are found, the parameter cannot be altered to
+      <literal>false</literal> inside a transaction block.
+     </para>
     </listitem>
    </varlistentry>
 
diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index 495f99a357..9121195725 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -2702,13 +2702,13 @@ checkGid(char *gid, Oid subid)
 }
 
 /*
- * LookupGXactBySubid
- *		Check if the prepared transaction done by apply worker exists.
+ * GetGidListBySubid
+ *      Get a list of GIDs which is PREPARE'd by the given subscription.
  */
-bool
-LookupGXactBySubid(Oid subid)
+List *
+GetGidListBySubid(Oid subid)
 {
-	bool		found = false;
+	List *list = NIL;
 
 	LWLockAcquire(TwoPhaseStateLock, LW_SHARED);
 	for (int i = 0; i < TwoPhaseState->numPrepXacts; i++)
@@ -2717,11 +2717,10 @@ LookupGXactBySubid(Oid subid)
 
 		/* Ignore not-yet-valid GIDs. */
 		if (gxact->valid && checkGid(gxact->gid, subid))
-		{
-			found = true;
-			break;
-		}
+			list = lappend(list, pstrdup(gxact->gid));
+
 	}
 	LWLockRelease(TwoPhaseStateLock);
-	return found;
+
+	return list;
 }
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index 0d80d6e110..cf3e5c64b0 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -1178,6 +1178,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 				/* XXX */
 				if (IsSet(opts.specified_opts, SUBOPT_TWOPHASE_COMMIT))
 				{
+					List *prepared_xacts = NIL;
+
 					/*
 					 * two_phase can be only changed for disabled
 					 * subscriptions
@@ -1194,13 +1196,28 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 					 */
 					logicalrep_workers_stop(subid);
 
-					/* Check whether the number of prepared transactions */
+					/*
+					 * If two phase was enabled, there is a possibility the
+					 * transactions has already been PREPARE'd.
+					 */
 					if (!opts.twophase &&
 						form->subtwophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
-						LookupGXactBySubid(subid))
-						ereport(ERROR,
-								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-								 errmsg("cannot disable two_phase when uncommitted prepared transactions present")));
+						(prepared_xacts = GetGidListBySubid(subid)) != NIL)
+					{
+						ListCell	*cell;
+
+						/* Must not be in the transaction */
+						PreventInTransactionBlock(isTopLevel,
+												  "ALTER SUBSCRIPTION ... SET (two_phase = ...)");
+
+						/* Abort all listed transactions */
+						foreach(cell, prepared_xacts)
+						{
+							FinishPreparedTransaction((char *) lfirst(cell),
+													  false);
+							prepared_xacts = list_delete_cell(prepared_xacts, cell);
+						}
+					}
 
 					/* Change system catalog acoordingly */
 					values[Anum_pg_subscription_subtwophasestate - 1] =
diff --git a/src/include/access/twophase.h b/src/include/access/twophase.h
index d493ed24c5..95770bbd69 100644
--- a/src/include/access/twophase.h
+++ b/src/include/access/twophase.h
@@ -18,6 +18,7 @@
 #include "access/xlogdefs.h"
 #include "datatype/timestamp.h"
 #include "storage/lock.h"
+#include "nodes/pg_list.h"
 
 /*
  * GlobalTransactionData is defined in twophase.c; other places have no
@@ -63,6 +64,6 @@ extern void restoreTwoPhaseData(void);
 extern bool LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 						TimestampTz origin_prepare_timestamp);
 
-extern bool LookupGXactBySubid(Oid subid);
+extern List *GetGidListBySubid(Oid subid);
 
 #endif							/* TWOPHASE_H */
diff --git a/src/test/subscription/t/099_twophase_added.pl b/src/test/subscription/t/099_twophase_added.pl
index c13a37675a..a8135b671c 100644
--- a/src/test/subscription/t/099_twophase_added.pl
+++ b/src/test/subscription/t/099_twophase_added.pl
@@ -69,4 +69,39 @@ $result = $node_subscriber->safe_psql('postgres',
 is($result, q(5),
    "prepared transactions done before altering can be replicated");
 
+######
+# Check the case that prepared transactions exist on subscriber node
+######
+
+$node_publisher->safe_psql(
+	'postgres', "
+	BEGIN;
+	INSERT INTO tab_full VALUES (generate_series(6, 10));
+	PREPARE TRANSACTION 'test_prepared_tab_full';");
+
+$node_publisher->wait_for_catchup('sub');
+
+$result = $node_subscriber->safe_psql('postgres',
+    "SELECT count(*) FROM pg_prepared_xacts;");
+is($result, q(1), "transaction has been prepared on subscriber");
+
+$node_subscriber->safe_psql(
+    'postgres', "
+    ALTER SUBSCRIPTION sub DISABLE;
+    ALTER SUBSCRIPTION sub SET (two_phase = off);
+    ALTER SUBSCRIPTION sub ENABLE;");
+
+$result = $node_subscriber->safe_psql('postgres',
+    "SELECT count(*) FROM pg_prepared_xacts;");
+is($result, q(0), "prepared transaction done by worker is aborted");
+
+$node_publisher->safe_psql( 'postgres',
+    "COMMIT PREPARED 'test_prepared_tab_full';");
+$node_publisher->wait_for_catchup('sub');
+
+$result = $node_subscriber->safe_psql('postgres',
+    "SELECT count(10) FROM tab_full;");
+is($result, q(10),
+   "prepared transactions on publisher can be replicated");
+
 done_testing();
-- 
2.43.0

From f92c5166b808e70d7907b099c847dbffed8136c7 Mon Sep 17 00:00:00 2001
From: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Date: Fri, 19 Apr 2024 11:03:19 +0000
Subject: [PATCH v5 4/4] Add force_alter option

---
 src/backend/commands/subscriptioncmds.c       | 36 +++++++++++++++++--
 src/test/regress/expected/subscription.out    |  3 ++
 src/test/regress/sql/subscription.sql         |  3 ++
 src/test/subscription/t/099_twophase_added.pl | 23 +++++++++---
 4 files changed, 58 insertions(+), 7 deletions(-)

diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index cf3e5c64b0..33b789b730 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -73,6 +73,7 @@
 #define SUBOPT_FAILOVER				0x00002000
 #define SUBOPT_LSN					0x00004000
 #define SUBOPT_ORIGIN				0x00008000
+#define SUBOPT_FORCE_ALTER			0x00010000
 
 /* check if the 'val' has 'bits' set */
 #define IsSet(val, bits)  (((val) & (bits)) == (bits))
@@ -100,6 +101,7 @@ typedef struct SubOpts
 	bool		failover;
 	char	   *origin;
 	XLogRecPtr	lsn;
+	bool		twophase_force;
 } SubOpts;
 
 static List *fetch_table_list(WalReceiverConn *wrconn, List *publications);
@@ -162,6 +164,8 @@ parse_subscription_options(ParseState *pstate, List *stmt_options,
 		opts->failover = false;
 	if (IsSet(supported_opts, SUBOPT_ORIGIN))
 		opts->origin = pstrdup(LOGICALREP_ORIGIN_ANY);
+	if (IsSet(supported_opts, SUBOPT_FORCE_ALTER))
+		opts->twophase_force = false;
 
 	/* Parse options */
 	foreach(lc, stmt_options)
@@ -367,6 +371,15 @@ parse_subscription_options(ParseState *pstate, List *stmt_options,
 			opts->specified_opts |= SUBOPT_LSN;
 			opts->lsn = lsn;
 		}
+		else if (IsSet(supported_opts, SUBOPT_FORCE_ALTER) &&
+				 strcmp(defel->defname, "force_alter") == 0)
+		{
+			if (IsSet(opts->specified_opts, SUBOPT_FORCE_ALTER))
+				errorConflictingDefElem(defel, pstate);
+
+			opts->specified_opts |= SUBOPT_FORCE_ALTER;
+			opts->twophase_force = defGetBoolean(defel);
+		}
 		else
 			ereport(ERROR,
 					(errcode(ERRCODE_SYNTAX_ERROR),
@@ -1170,7 +1183,7 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 								  SUBOPT_DISABLE_ON_ERR |
 								  SUBOPT_PASSWORD_REQUIRED |
 								  SUBOPT_RUN_AS_OWNER | SUBOPT_FAILOVER |
-								  SUBOPT_ORIGIN);
+								  SUBOPT_ORIGIN | SUBOPT_FORCE_ALTER);
 
 				parse_subscription_options(pstate, stmt->options,
 										   supported_opts, &opts);
@@ -1206,6 +1219,16 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 					{
 						ListCell	*cell;
 
+						/*
+						 * Abort prepared transactions if force option is also
+						 * specified. Otherwise raise an ERROR.
+						 */
+						if (!opts.twophase_force)
+							ereport(ERROR,
+									(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+									 errmsg("cannot alter %s when there are prepared transactions",
+											"two_phase = false")));
+
 						/* Must not be in the transaction */
 						PreventInTransactionBlock(isTopLevel,
 												  "ALTER SUBSCRIPTION ... SET (two_phase = ...)");
@@ -1215,8 +1238,9 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 						{
 							FinishPreparedTransaction((char *) lfirst(cell),
 													  false);
-							prepared_xacts = list_delete_cell(prepared_xacts, cell);
 						}
+
+						list_free(prepared_xacts);
 					}
 
 					/* Change system catalog acoordingly */
@@ -1333,6 +1357,14 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 					replaces[Anum_pg_subscription_suborigin - 1] = true;
 				}
 
+				/* force_alter cannot be used standalone */
+				if (IsSet(opts.specified_opts, SUBOPT_FORCE_ALTER) &&
+					!IsSet(opts.specified_opts, SUBOPT_TWOPHASE_COMMIT))
+					ereport(ERROR,
+							(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+							 errmsg("%s must be specified with %s",
+									"force_alter", "two_phase")));
+
 				update_tuple = true;
 				break;
 			}
diff --git a/src/test/regress/expected/subscription.out b/src/test/regress/expected/subscription.out
index 9bba656e00..16154d1bee 100644
--- a/src/test/regress/expected/subscription.out
+++ b/src/test/regress/expected/subscription.out
@@ -372,6 +372,9 @@ ERROR:  two_phase requires a Boolean value
 CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUBLICATION testpub WITH (connect = false, two_phase = true);
 WARNING:  subscription was created, but is not connected
 HINT:  To initiate replication, you must manually create the replication slot, enable the subscription, and refresh the subscription.
+-- fail - force_alter cannot be set alone
+ALTER SUBSCRIPTION regress_testsub SET (force_alter = true);
+ERROR:  force_alter must be specified with two_phase
 \dRs+
                                                                                                                 List of subscriptions
       Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
diff --git a/src/test/regress/sql/subscription.sql b/src/test/regress/sql/subscription.sql
index 9ff151f806..8d8f5bb670 100644
--- a/src/test/regress/sql/subscription.sql
+++ b/src/test/regress/sql/subscription.sql
@@ -256,6 +256,9 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 -- now it works
 CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUBLICATION testpub WITH (connect = false, two_phase = true);
 
+-- fail - force_alter cannot be set alone
+ALTER SUBSCRIPTION regress_testsub SET (force_alter = true);
+
 \dRs+
 -- We can alter streaming when two_phase enabled
 ALTER SUBSCRIPTION regress_testsub SET (streaming = true);
diff --git a/src/test/subscription/t/099_twophase_added.pl b/src/test/subscription/t/099_twophase_added.pl
index a8135b671c..7c73a58f2a 100644
--- a/src/test/subscription/t/099_twophase_added.pl
+++ b/src/test/subscription/t/099_twophase_added.pl
@@ -85,16 +85,29 @@ $result = $node_subscriber->safe_psql('postgres',
     "SELECT count(*) FROM pg_prepared_xacts;");
 is($result, q(1), "transaction has been prepared on subscriber");
 
-$node_subscriber->safe_psql(
-    'postgres', "
-    ALTER SUBSCRIPTION sub DISABLE;
-    ALTER SUBSCRIPTION sub SET (two_phase = off);
-    ALTER SUBSCRIPTION sub ENABLE;");
+$node_subscriber->safe_psql('postgres', "ALTER SUBSCRIPTION sub DISABLE;");
+
+my $stdout;
+my $stderr;
+
+($result, $stdout, $stderr) = $node_subscriber->psql(
+	'postgres', "ALTER SUBSCRIPTION sub SET (two_phase = off);");
+ok($stderr =~ /cannot alter two_phase = false when there are prepared transactions/,
+	'ALTER SUBSCRIPTION failed');
+
+$result = $node_subscriber->safe_psql('postgres',
+    "SELECT count(*) FROM pg_prepared_xacts;");
+is($result, q(1), "prepared transaction still exits");
+
+$node_subscriber->safe_psql('postgres',
+    "ALTER SUBSCRIPTION sub SET (two_phase = off, force_alter = on);");
 
 $result = $node_subscriber->safe_psql('postgres',
     "SELECT count(*) FROM pg_prepared_xacts;");
 is($result, q(0), "prepared transaction done by worker is aborted");
 
+$node_subscriber->safe_psql('postgres', "ALTER SUBSCRIPTION sub ENABLE;");
+
 $node_publisher->safe_psql( 'postgres',
     "COMMIT PREPARED 'test_prepared_tab_full';");
 $node_publisher->wait_for_catchup('sub');
-- 
2.43.0

From e5c865867983282814c60723499546913fd2d8c1 Mon Sep 17 00:00:00 2001
From: Ajin Cherian <ajinc@fast.au.fujitsu.com>
Date: Fri, 5 Apr 2024 06:47:18 -0400
Subject: [PATCH 1/4] Allow altering of two_phase option of a SUBSCRIPTION

This patch allows user to alter two_phase option of a subscriber provided no uncommitted
prepared transactions are pending on that subscription.

Author: Cherian Ajin, Hayato Kuroda
---
 src/backend/access/transam/twophase.c         | 43 ++++++++++
 src/backend/commands/subscriptioncmds.c       | 83 ++++++++++++++++---
 src/backend/nodes/gen_node_support.pl         |  2 +-
 .../libpqwalreceiver/libpqwalreceiver.c       | 30 +++++++
 src/backend/replication/logical/launcher.c    | 21 +++++
 src/backend/replication/logical/worker.c      |  2 +-
 src/backend/replication/repl_gram.y           | 20 ++++-
 src/backend/replication/repl_scanner.l        |  2 +
 src/backend/replication/slot.c                | 25 ++++++
 src/backend/replication/walsender.c           | 47 +++++++++++
 src/bin/psql/tab-complete.c                   |  2 +-
 src/include/access/twophase.h                 |  3 +
 src/include/nodes/replnodes.h                 | 12 +++
 src/include/replication/slot.h                |  2 +-
 src/include/replication/walreceiver.h         | 10 +++
 src/include/replication/worker_internal.h     |  1 +
 src/test/regress/expected/subscription.out    |  5 +-
 src/test/regress/sql/subscription.sql         |  5 +-
 src/test/subscription/t/021_twophase.pl       | 67 ++++++++++++++-
 19 files changed, 354 insertions(+), 28 deletions(-)

diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index c6af8cfd7e..2148daba3c 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -2658,3 +2658,46 @@ LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 	LWLockRelease(TwoPhaseStateLock);
 	return found;
 }
+
+/*
+ * checkGid
+ */
+static bool
+checkGid(char *gid, Oid subid)
+{
+	int			ret;
+	Oid			subid_written,
+				xid;
+
+	ret = sscanf(gid, "pg_gid_%u_%u", &subid_written, &xid);
+
+	if (ret != 2 || subid != subid_written)
+		return false;
+
+	return true;
+}
+
+/*
+ * LookupGXactBySubid
+ *		Check if the prepared transaction done by apply worker exists.
+ */
+bool
+LookupGXactBySubid(Oid subid)
+{
+	bool		found = false;
+
+	LWLockAcquire(TwoPhaseStateLock, LW_SHARED);
+	for (int i = 0; i < TwoPhaseState->numPrepXacts; i++)
+	{
+		GlobalTransaction gxact = TwoPhaseState->prepXacts[i];
+
+		/* Ignore not-yet-valid GIDs. */
+		if (gxact->valid && checkGid(gxact->gid, subid))
+		{
+			found = true;
+			break;
+		}
+	}
+	LWLockRelease(TwoPhaseStateLock);
+	return found;
+}
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index 6fe111e98d..59852fd9af 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -16,6 +16,7 @@
 
 #include "access/htup_details.h"
 #include "access/table.h"
+#include "access/twophase.h"
 #include "access/xact.h"
 #include "catalog/catalog.h"
 #include "catalog/dependency.h"
@@ -1130,13 +1131,49 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 			{
 				supported_opts = (SUBOPT_SLOT_NAME |
 								  SUBOPT_SYNCHRONOUS_COMMIT | SUBOPT_BINARY |
-								  SUBOPT_STREAMING | SUBOPT_DISABLE_ON_ERR |
+								  SUBOPT_STREAMING | SUBOPT_TWOPHASE_COMMIT |
+								  SUBOPT_DISABLE_ON_ERR |
 								  SUBOPT_PASSWORD_REQUIRED |
 								  SUBOPT_RUN_AS_OWNER | SUBOPT_ORIGIN);
 
 				parse_subscription_options(pstate, stmt->options,
 										   supported_opts, &opts);
 
+				/* XXX */
+				if (IsSet(opts.specified_opts, SUBOPT_TWOPHASE_COMMIT))
+				{
+					/*
+					 * two_phase can be only changed for disabled
+					 * subscriptions
+					 */
+					if (form->subenabled)
+						ereport(ERROR,
+								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+								 errmsg("cannot set %s for enabled subscription",
+										"two_phase")));
+
+					/*
+					 * Stop all the subscription workers, just in case. Workers
+					 * may still survive even if the subscription is disabled.
+					 */
+					logicalrep_workers_stop(subid);
+
+					/* Check whether the number of prepared transactions */
+					if (!opts.twophase &&
+						form->subtwophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
+						LookupGXactBySubid(subid))
+						ereport(ERROR,
+								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+								 errmsg("cannot disable two_phase when uncommitted prepared transactions present")));
+
+					/* Change system catalog acoordingly */
+					values[Anum_pg_subscription_subtwophasestate - 1] =
+						CharGetDatum(opts.twophase ?
+									 LOGICALREP_TWOPHASE_STATE_PENDING :
+									 LOGICALREP_TWOPHASE_STATE_DISABLED);
+					replaces[Anum_pg_subscription_subtwophasestate - 1] = true;
+				}
+
 				if (IsSet(opts.specified_opts, SUBOPT_SLOT_NAME))
 				{
 					/*
@@ -1453,6 +1490,38 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 		heap_freetuple(tup);
 	}
 
+	/*
+	 * Try to acquire the connection necessary for altering slot.
+	 */
+	if (replaces[Anum_pg_subscription_subtwophasestate - 1])
+	{
+		bool		must_use_password;
+		char	   *err;
+		WalReceiverConn *wrconn;
+
+		/* Load the library providing us libpq calls. */
+		load_file("libpqwalreceiver", false);
+
+		/* Try to connect to the publisher */
+		must_use_password = (!superuser() && opts.passwordrequired);
+		wrconn = walrcv_connect(sub->conninfo, true, must_use_password,
+								sub->name, &err);
+		if (!wrconn)
+			ereport(ERROR,
+					(errcode(ERRCODE_CONNECTION_FAILURE),
+					 errmsg("could not connect to the publisher: %s", err)));
+
+		PG_TRY();
+		{
+			walrcv_alter_slot(wrconn, sub->slotname, opts.twophase);
+		}
+		PG_FINALLY();
+		{
+			walrcv_disconnect(wrconn);
+		}
+		PG_END_TRY();
+	}
+
 	table_close(rel, RowExclusiveLock);
 
 	ObjectAddressSet(myself, SubscriptionRelationId, subid);
@@ -1481,7 +1550,6 @@ DropSubscription(DropSubscriptionStmt *stmt, bool isTopLevel)
 	char	   *subname;
 	char	   *conninfo;
 	char	   *slotname;
-	List	   *subworkers;
 	ListCell   *lc;
 	char		originname[NAMEDATALEN];
 	char	   *err = NULL;
@@ -1591,16 +1659,7 @@ DropSubscription(DropSubscriptionStmt *stmt, bool isTopLevel)
 	 * New workers won't be started because we hold an exclusive lock on the
 	 * subscription till the end of the transaction.
 	 */
-	LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
-	subworkers = logicalrep_workers_find(subid, false);
-	LWLockRelease(LogicalRepWorkerLock);
-	foreach(lc, subworkers)
-	{
-		LogicalRepWorker *w = (LogicalRepWorker *) lfirst(lc);
-
-		logicalrep_worker_stop(w->subid, w->relid);
-	}
-	list_free(subworkers);
+	logicalrep_workers_stop(subid);
 
 	/*
 	 * Remove the no-longer-useful entry in the launcher's table of apply
diff --git a/src/backend/nodes/gen_node_support.pl b/src/backend/nodes/gen_node_support.pl
index d67565b925..fcba6f986f 100644
--- a/src/backend/nodes/gen_node_support.pl
+++ b/src/backend/nodes/gen_node_support.pl
@@ -107,7 +107,7 @@ my @nodetag_only_files = qw(
 # ABI stability during development.
 
 my $last_nodetag = 'WindowObjectData';
-my $last_nodetag_no = 454;
+my $last_nodetag_no = 455;
 
 # output file names
 my @output_files;
diff --git a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
index b4038e114d..815ab8f9df 100644
--- a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
+++ b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
@@ -75,6 +75,8 @@ static char *libpqrcv_create_slot(WalReceiverConn *conn,
 								  bool two_phase,
 								  CRSSnapshotAction snapshot_action,
 								  XLogRecPtr *lsn);
+static void libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
+								bool two_phase);
 static pid_t libpqrcv_get_backend_pid(WalReceiverConn *conn);
 static WalRcvExecResult *libpqrcv_exec(WalReceiverConn *conn,
 									   const char *query,
@@ -95,6 +97,7 @@ static WalReceiverFunctionsType PQWalReceiverFunctions = {
 	.walrcv_receive = libpqrcv_receive,
 	.walrcv_send = libpqrcv_send,
 	.walrcv_create_slot = libpqrcv_create_slot,
+	.walrcv_alter_slot = libpqrcv_alter_slot,
 	.walrcv_get_backend_pid = libpqrcv_get_backend_pid,
 	.walrcv_exec = libpqrcv_exec,
 	.walrcv_disconnect = libpqrcv_disconnect
@@ -1039,6 +1042,33 @@ libpqrcv_create_slot(WalReceiverConn *conn, const char *slotname,
 	return snapshot;
 }
 
+/*
+ * Change the definition of the replication slot.
+ */
+static void
+libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
+					bool two_phase)
+{
+	StringInfoData cmd;
+	PGresult   *res;
+
+	initStringInfo(&cmd);
+	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( TWO_PHASE %s )",
+					 quote_identifier(slotname),
+					 two_phase ? "true" : "false");
+
+	res = libpqrcv_PQexec(conn->streamConn, cmd.data);
+	pfree(cmd.data);
+
+	if (PQresultStatus(res) != PGRES_COMMAND_OK)
+		ereport(ERROR,
+				(errcode(ERRCODE_PROTOCOL_VIOLATION),
+				 errmsg("could not alter replication slot \"%s\": %s",
+						slotname, pchomp(PQerrorMessage(conn->streamConn)))));
+
+	PQclear(res);
+}
+
 /*
  * Return PID of remote backend process.
  */
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 8395ae7b23..295fe0f2a0 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -608,6 +608,27 @@ logicalrep_worker_stop(Oid subid, Oid relid)
 	LWLockRelease(LogicalRepWorkerLock);
 }
 
+/*
+ * Stop all the subscription workers.
+ */
+void
+logicalrep_workers_stop(Oid subid)
+{
+	List	   *subworkers;
+	ListCell   *lc;
+
+	LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
+	subworkers = logicalrep_workers_find(subid, false);
+	LWLockRelease(LogicalRepWorkerLock);
+	foreach(lc, subworkers)
+	{
+		LogicalRepWorker *w = (LogicalRepWorker *) lfirst(lc);
+
+		logicalrep_worker_stop(w->subid, w->relid);
+	}
+	list_free(subworkers);
+}
+
 /*
  * Stop the given logical replication parallel apply worker.
  *
diff --git a/src/backend/replication/logical/worker.c b/src/backend/replication/logical/worker.c
index 832b1cf764..7da6d546dd 100644
--- a/src/backend/replication/logical/worker.c
+++ b/src/backend/replication/logical/worker.c
@@ -3926,7 +3926,7 @@ maybe_reread_subscription(void)
 	/* !slotname should never happen when enabled is true. */
 	Assert(newsub->slotname);
 
-	/* two-phase should not be altered */
+	/* two-phase should not be altered while the worker exists */
 	Assert(newsub->twophasestate == MySubscription->twophasestate);
 
 	/*
diff --git a/src/backend/replication/repl_gram.y b/src/backend/replication/repl_gram.y
index 0c874e33cf..bff501263e 100644
--- a/src/backend/replication/repl_gram.y
+++ b/src/backend/replication/repl_gram.y
@@ -64,6 +64,7 @@ Node *replication_parse_result;
 %token K_START_REPLICATION
 %token K_CREATE_REPLICATION_SLOT
 %token K_DROP_REPLICATION_SLOT
+%token K_ALTER_REPLICATION_SLOT
 %token K_TIMELINE_HISTORY
 %token K_WAIT
 %token K_TIMELINE
@@ -79,8 +80,9 @@ Node *replication_parse_result;
 
 %type <node>	command
 %type <node>	base_backup start_replication start_logical_replication
-				create_replication_slot drop_replication_slot identify_system
-				read_replication_slot timeline_history show
+				create_replication_slot drop_replication_slot
+				alter_replication_slot identify_system read_replication_slot
+				timeline_history show
 %type <list>	generic_option_list
 %type <defelt>	generic_option
 %type <uintval>	opt_timeline
@@ -111,6 +113,7 @@ command:
 			| start_logical_replication
 			| create_replication_slot
 			| drop_replication_slot
+			| alter_replication_slot
 			| read_replication_slot
 			| timeline_history
 			| show
@@ -257,6 +260,18 @@ drop_replication_slot:
 				}
 			;
 
+/* ALTER_REPLICATION_SLOT slot (options) */
+alter_replication_slot:
+			K_ALTER_REPLICATION_SLOT IDENT '(' generic_option_list ')'
+				{
+					AlterReplicationSlotCmd *cmd;
+					cmd = makeNode(AlterReplicationSlotCmd);
+					cmd->slotname = $2;
+					cmd->options = $4;
+					$$ = (Node *) cmd;
+				}
+			;
+
 /*
  * START_REPLICATION [SLOT slot] [PHYSICAL] %X/%X [TIMELINE %d]
  */
@@ -399,6 +414,7 @@ ident_or_keyword:
 			| K_START_REPLICATION			{ $$ = "start_replication"; }
 			| K_CREATE_REPLICATION_SLOT	{ $$ = "create_replication_slot"; }
 			| K_DROP_REPLICATION_SLOT		{ $$ = "drop_replication_slot"; }
+			| K_ALTER_REPLICATION_SLOT		{ $$ = "alter_replication_slot"; }
 			| K_TIMELINE_HISTORY			{ $$ = "timeline_history"; }
 			| K_WAIT						{ $$ = "wait"; }
 			| K_TIMELINE					{ $$ = "timeline"; }
diff --git a/src/backend/replication/repl_scanner.l b/src/backend/replication/repl_scanner.l
index cb467ca46f..6396463cf9 100644
--- a/src/backend/replication/repl_scanner.l
+++ b/src/backend/replication/repl_scanner.l
@@ -125,6 +125,7 @@ TIMELINE			{ return K_TIMELINE; }
 START_REPLICATION	{ return K_START_REPLICATION; }
 CREATE_REPLICATION_SLOT		{ return K_CREATE_REPLICATION_SLOT; }
 DROP_REPLICATION_SLOT		{ return K_DROP_REPLICATION_SLOT; }
+ALTER_REPLICATION_SLOT		{ return K_ALTER_REPLICATION_SLOT; }
 TIMELINE_HISTORY	{ return K_TIMELINE_HISTORY; }
 PHYSICAL			{ return K_PHYSICAL; }
 RESERVE_WAL			{ return K_RESERVE_WAL; }
@@ -301,6 +302,7 @@ replication_scanner_is_replication_command(void)
 		case K_START_REPLICATION:
 		case K_CREATE_REPLICATION_SLOT:
 		case K_DROP_REPLICATION_SLOT:
+		case K_ALTER_REPLICATION_SLOT:
 		case K_READ_REPLICATION_SLOT:
 		case K_TIMELINE_HISTORY:
 		case K_SHOW:
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 1f9d0ed9b3..04915590d2 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -648,6 +648,31 @@ ReplicationSlotDrop(const char *name, bool nowait)
 	ReplicationSlotDropAcquired();
 }
 
+/*
+ * Change the definition of the slot identified by the specified name.
+ */
+void
+ReplicationSlotAlter(const char *name, bool two_phase)
+{
+	Assert(MyReplicationSlot == NULL);
+
+	ReplicationSlotAcquire(name, false);
+
+	if (SlotIsPhysical(MyReplicationSlot))
+		ereport(ERROR,
+				errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				errmsg("cannot use %s with a physical replication slot",
+					   "ALTER_REPLICATION_SLOT"));
+
+	SpinLockAcquire(&MyReplicationSlot->mutex);
+	MyReplicationSlot->data.two_phase = two_phase;
+	SpinLockRelease(&MyReplicationSlot->mutex);
+
+	ReplicationSlotMarkDirty();
+	ReplicationSlotSave();
+	ReplicationSlotRelease();
+}
+
 /*
  * Permanently drop the currently acquired replication slot.
  */
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 4c53de08b9..4c18dadaad 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1247,6 +1247,46 @@ DropReplicationSlot(DropReplicationSlotCmd *cmd)
 	ReplicationSlotDrop(cmd->slotname, !cmd->wait);
 }
 
+/*
+ * Process extra options given to ALTER_REPLICATION_SLOT.
+ */
+static void
+ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd, bool *two_phase)
+{
+	bool		two_phase_given = false;
+	ListCell   *lc;
+
+	/* Parse options */
+	foreach(lc, cmd->options)
+	{
+		DefElem    *defel = (DefElem *) lfirst(lc);
+
+		if (strcmp(defel->defname, "two_phase") == 0)
+		{
+			if (two_phase_given)
+				ereport(ERROR,
+						(errcode(ERRCODE_SYNTAX_ERROR),
+						 errmsg("conflicting or redundant options")));
+			two_phase_given = true;
+			*two_phase = defGetBoolean(defel);
+		}
+		else
+			elog(ERROR, "unrecognized option: %s", defel->defname);
+	}
+}
+
+/*
+ * Change the definition of a replication slot.
+ */
+static void
+AlterReplicationSlot(AlterReplicationSlotCmd *cmd)
+{
+	bool		two_phase = false;
+
+	ParseAlterReplSlotOptions(cmd, &two_phase);
+	ReplicationSlotAlter(cmd->slotname, two_phase);
+}
+
 /*
  * Load previously initiated logical slot and prepare for sending data (via
  * WalSndLoop).
@@ -1820,6 +1860,13 @@ exec_replication_command(const char *cmd_string)
 			EndReplicationCommand(cmdtag);
 			break;
 
+		case T_AlterReplicationSlotCmd:
+			cmdtag = "ALTER_REPLICATION_SLOT";
+			set_ps_display(cmdtag);
+			AlterReplicationSlot((AlterReplicationSlotCmd *) cmd_node);
+			EndReplicationCommand(cmdtag);
+			break;
+
 		case T_StartReplicationCmd:
 			{
 				StartReplicationCmd *cmd = (StartReplicationCmd *) cmd_node;
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
index a1aa946b30..b689b6906a 100644
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -1927,7 +1927,7 @@ psql_completion(const char *text, int start, int end)
 	else if (HeadMatches("ALTER", "SUBSCRIPTION", MatchAny) && TailMatches("SET", "("))
 		COMPLETE_WITH("binary", "disable_on_error", "origin",
 					  "password_required", "run_as_owner", "slot_name",
-					  "streaming", "synchronous_commit");
+					  "streaming", "synchronous_commit", "two_phase");
 	/* ALTER SUBSCRIPTION <name> SKIP ( */
 	else if (HeadMatches("ALTER", "SUBSCRIPTION", MatchAny) && TailMatches("SKIP", "("))
 		COMPLETE_WITH("lsn");
diff --git a/src/include/access/twophase.h b/src/include/access/twophase.h
index 21e2af7387..dac3f27bc3 100644
--- a/src/include/access/twophase.h
+++ b/src/include/access/twophase.h
@@ -62,4 +62,7 @@ extern void PrepareRedoRemove(TransactionId xid, bool giveWarning);
 extern void restoreTwoPhaseData(void);
 extern bool LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 						TimestampTz origin_prepare_timestamp);
+
+extern bool LookupGXactBySubid(Oid subid);
+
 #endif							/* TWOPHASE_H */
diff --git a/src/include/nodes/replnodes.h b/src/include/nodes/replnodes.h
index 4321ba8f86..5819276d19 100644
--- a/src/include/nodes/replnodes.h
+++ b/src/include/nodes/replnodes.h
@@ -72,6 +72,18 @@ typedef struct DropReplicationSlotCmd
 } DropReplicationSlotCmd;
 
 
+/* ----------------------
+ *		ALTER_REPLICATION_SLOT command
+ * ----------------------
+ */
+typedef struct AlterReplicationSlotCmd
+{
+	NodeTag		type;
+	char	   *slotname;
+	List	   *options;
+} AlterReplicationSlotCmd;
+
+
 /* ----------------------
  *		START_REPLICATION command
  * ----------------------
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index a8a89dc784..24ab5117bd 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -214,7 +214,7 @@ extern void ReplicationSlotCreate(const char *name, bool db_specific,
 								  bool two_phase);
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
-
+extern void ReplicationSlotAlter(const char *name, bool two_phase);
 extern void ReplicationSlotAcquire(const char *name, bool nowait);
 extern void ReplicationSlotRelease(void);
 extern void ReplicationSlotCleanup(void);
diff --git a/src/include/replication/walreceiver.h b/src/include/replication/walreceiver.h
index 281626fa6f..8ba1599fad 100644
--- a/src/include/replication/walreceiver.h
+++ b/src/include/replication/walreceiver.h
@@ -359,6 +359,13 @@ typedef char *(*walrcv_create_slot_fn) (WalReceiverConn *conn,
 										CRSSnapshotAction snapshot_action,
 										XLogRecPtr *lsn);
 
+/*
+ * walrcv_alter_slot_fn
+ */
+typedef void (*walrcv_alter_slot_fn) (WalReceiverConn *conn,
+									  const char *slotname,
+									  bool two_phase);
+
 /*
  * walrcv_get_backend_pid_fn
  *
@@ -400,6 +407,7 @@ typedef struct WalReceiverFunctionsType
 	walrcv_receive_fn walrcv_receive;
 	walrcv_send_fn walrcv_send;
 	walrcv_create_slot_fn walrcv_create_slot;
+	walrcv_alter_slot_fn walrcv_alter_slot;
 	walrcv_get_backend_pid_fn walrcv_get_backend_pid;
 	walrcv_exec_fn walrcv_exec;
 	walrcv_disconnect_fn walrcv_disconnect;
@@ -431,6 +439,8 @@ extern PGDLLIMPORT WalReceiverFunctionsType *WalReceiverFunctions;
 	WalReceiverFunctions->walrcv_send(conn, buffer, nbytes)
 #define walrcv_create_slot(conn, slotname, temporary, two_phase, snapshot_action, lsn) \
 	WalReceiverFunctions->walrcv_create_slot(conn, slotname, temporary, two_phase, snapshot_action, lsn)
+#define walrcv_alter_slot(conn, slotname, two_phase) \
+	WalReceiverFunctions->walrcv_alter_slot(conn, slotname, two_phase)
 #define walrcv_get_backend_pid(conn) \
 	WalReceiverFunctions->walrcv_get_backend_pid(conn)
 #define walrcv_exec(conn, exec, nRetTypes, retTypes) \
diff --git a/src/include/replication/worker_internal.h b/src/include/replication/worker_internal.h
index 343e781896..3f19ae4f5f 100644
--- a/src/include/replication/worker_internal.h
+++ b/src/include/replication/worker_internal.h
@@ -235,6 +235,7 @@ extern bool logicalrep_worker_launch(Oid dbid, Oid subid, const char *subname,
 									 Oid userid, Oid relid,
 									 dsm_handle subworker_dsm);
 extern void logicalrep_worker_stop(Oid subid, Oid relid);
+extern void logicalrep_workers_stop(Oid subid);
 extern void logicalrep_pa_worker_stop(ParallelApplyWorkerInfo *winfo);
 extern void logicalrep_worker_wakeup(Oid subid, Oid relid);
 extern void logicalrep_worker_wakeup_ptr(LogicalRepWorker *worker);
diff --git a/src/test/regress/expected/subscription.out b/src/test/regress/expected/subscription.out
index b15eddbff3..51c466f42e 100644
--- a/src/test/regress/expected/subscription.out
+++ b/src/test/regress/expected/subscription.out
@@ -377,10 +377,7 @@ HINT:  To initiate replication, you must manually create the replication slot, e
  regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | p                | f                | any    | t                 | f             | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
---fail - alter of two_phase option not supported.
-ALTER SUBSCRIPTION regress_testsub SET (two_phase = false);
-ERROR:  unrecognized subscription parameter: "two_phase"
--- but can alter streaming when two_phase enabled
+-- We can alter streaming when two_phase enabled
 ALTER SUBSCRIPTION regress_testsub SET (streaming = true);
 \dRs+
                                                                                                            List of subscriptions
diff --git a/src/test/regress/sql/subscription.sql b/src/test/regress/sql/subscription.sql
index 444e563ff3..b7764c1074 100644
--- a/src/test/regress/sql/subscription.sql
+++ b/src/test/regress/sql/subscription.sql
@@ -256,10 +256,7 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUBLICATION testpub WITH (connect = false, two_phase = true);
 
 \dRs+
---fail - alter of two_phase option not supported.
-ALTER SUBSCRIPTION regress_testsub SET (two_phase = false);
-
--- but can alter streaming when two_phase enabled
+-- We can alter streaming when two_phase enabled
 ALTER SUBSCRIPTION regress_testsub SET (streaming = true);
 
 \dRs+
diff --git a/src/test/subscription/t/021_twophase.pl b/src/test/subscription/t/021_twophase.pl
index 8ce4cfc983..b6ce59763a 100644
--- a/src/test/subscription/t/021_twophase.pl
+++ b/src/test/subscription/t/021_twophase.pl
@@ -367,6 +367,71 @@ $result =
   $node_subscriber->safe_psql('postgres', "SELECT count(*) FROM tab_copy;");
 is($result, qq(2), 'replicated data in subscriber table');
 
+# Disable the subscription and alter it to two_phase = false,
+# verify that the altered subscription reflects the two_phase option.
+
+# Alter subscription two_phase to false
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy DISABLE");
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = false)");
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy ENABLE");
+
+# Wait for subscription startup
+$node_subscriber->wait_for_subscription_sync($node_publisher, $appname_copy);
+
+# Make sure that the two-phase is disabled on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+       "SELECT subtwophasestate FROM pg_subscription WHERE subname = 'tap_sub_copy';"
+);
+is($result, qq(d), 'two-phase is disabled');
+
+# Now do a prepare on publisher and make sure that it is not replicated.
+$node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub");
+$node_publisher->safe_psql(
+       'postgres', qq{
+    BEGIN;
+    INSERT INTO tab_copy VALUES (100);
+    PREPARE TRANSACTION 'newgid';
+	});
+
+# Wait for the subscriber to catchup
+$node_publisher->wait_for_catchup($appname_copy);
+
+# Make sure that there is 0 prepared transaction on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT count(*) FROM pg_prepared_xacts;");
+is($result, qq(0), 'transaction is prepared on subscriber');
+
+# Now commit the insert and verify that it IS replicated
+$node_publisher->safe_psql('postgres', "COMMIT PREPARED 'newgid';");
+
+# Wait for the subscriber to catchup
+$node_publisher->wait_for_catchup($appname_copy);
+
+# Made sure that the commited transaction is replicated.
+$result =
+	$node_subscriber->safe_psql('postgres', "SELECT count(*) FROM tab_copy;");
+is($result, qq(3), 'replicated data in subscriber table');
+
+# Alter subscription two_phase to true
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy DISABLE");
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = true)");
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy ENABLE");
+
+# Wait for subscription startup
+$node_subscriber->wait_for_subscription_sync($node_publisher, $appname_copy);
+
+# Make sure that the two-phase is enabled on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT subtwophasestate FROM pg_subscription WHERE subname = 'tap_sub_copy';"
+);
+is($result, qq(e), 'two-phase is disabled');
+
 $node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub_copy;");
 $node_publisher->safe_psql('postgres', "DROP PUBLICATION tap_pub_copy;");
 
@@ -374,8 +439,6 @@ $node_publisher->safe_psql('postgres', "DROP PUBLICATION tap_pub_copy;");
 # check all the cleanup
 ###############################
 
-$node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub");
-
 $result = $node_subscriber->safe_psql('postgres',
 	"SELECT count(*) FROM pg_subscription");
 is($result, qq(0), 'check subscription was dropped on subscriber');
-- 
2.43.0

From 9adc3d08178b89a95f9e87b76743a796814aaf8f Mon Sep 17 00:00:00 2001
From: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Date: Wed, 17 Apr 2024 06:18:23 +0000
Subject: [PATCH 2/4] Alter slot option two_phase only when altering true to
 false

---
 src/backend/commands/subscriptioncmds.c       |  3 +-
 src/test/subscription/meson.build             |  1 +
 src/test/subscription/t/099_twophase_added.pl | 72 +++++++++++++++++++
 3 files changed, 75 insertions(+), 1 deletion(-)
 create mode 100644 src/test/subscription/t/099_twophase_added.pl

diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index 59852fd9af..955d5e4899 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -1493,7 +1493,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 	/*
 	 * Try to acquire the connection necessary for altering slot.
 	 */
-	if (replaces[Anum_pg_subscription_subtwophasestate - 1])
+	if (replaces[Anum_pg_subscription_subtwophasestate - 1] &&
+		!opts.twophase)
 	{
 		bool		must_use_password;
 		char	   *err;
diff --git a/src/test/subscription/meson.build b/src/test/subscription/meson.build
index bd673a9d68..9e2a458202 100644
--- a/src/test/subscription/meson.build
+++ b/src/test/subscription/meson.build
@@ -40,6 +40,7 @@ tests += {
       't/031_column_list.pl',
       't/032_subscribe_use_index.pl',
       't/033_run_as_table_owner.pl',
+      't/099_twophase_added.pl',
       't/100_bugs.pl',
     ],
   },
diff --git a/src/test/subscription/t/099_twophase_added.pl b/src/test/subscription/t/099_twophase_added.pl
new file mode 100644
index 0000000000..c13a37675a
--- /dev/null
+++ b/src/test/subscription/t/099_twophase_added.pl
@@ -0,0 +1,72 @@
+# Copyright (c) 2021-2024, PostgreSQL Global Development Group
+
+# Additional tests for altering two_phase option
+use strict;
+use warnings FATAL => 'all';
+use PostgreSQL::Test::Cluster;
+use PostgreSQL::Test::Utils;
+use Test::More;
+
+# Initialize publisher node
+my $node_publisher = PostgreSQL::Test::Cluster->new('publisher');
+$node_publisher->init(allows_streaming => 'logical');
+$node_publisher->append_conf('postgresql.conf',
+	qq(max_prepared_transactions = 10));
+$node_publisher->start;
+
+# Create subscriber node
+my $node_subscriber = PostgreSQL::Test::Cluster->new('subscriber');
+$node_subscriber->init;
+$node_subscriber->append_conf('postgresql.conf',
+	qq(max_prepared_transactions = 10));
+$node_subscriber->start;
+
+# Define pre-existing tables on both nodes
+$node_publisher->safe_psql('postgres',
+    "CREATE TABLE tab_full (a int PRIMARY KEY);");
+$node_subscriber->safe_psql('postgres',
+	"CREATE TABLE tab_full (a int PRIMARY KEY)");
+
+# Setup logical replication, with two_phase = off
+my $publisher_connstr = $node_publisher->connstr . ' dbname=postgres';
+$node_publisher->safe_psql('postgres',
+	"CREATE PUBLICATION pub FOR ALL TABLES");
+
+$node_subscriber->safe_psql(
+	'postgres', "
+	CREATE SUBSCRIPTION sub
+	CONNECTION '$publisher_connstr' PUBLICATION pub
+	WITH (two_phase = off, copy_data = off)");
+
+######
+# Check the case that prepared transactions exist on publisher node
+######
+
+$node_publisher->safe_psql(
+	'postgres', "
+	BEGIN;
+	INSERT INTO tab_full VALUES (generate_series(1, 5));
+	PREPARE TRANSACTION 'test_prepared_tab_full';");
+
+$node_publisher->wait_for_catchup('sub');
+
+my $result = $node_subscriber->safe_psql('postgres',
+    "SELECT count(*) FROM pg_prepared_xacts;");
+is($result, q(0), "transaction is not prepared on subscriber");
+
+$node_subscriber->safe_psql(
+    'postgres', "
+    ALTER SUBSCRIPTION sub DISABLE;
+    ALTER SUBSCRIPTION sub SET (two_phase = on);
+    ALTER SUBSCRIPTION sub ENABLE;");
+
+$node_publisher->safe_psql( 'postgres',
+    "COMMIT PREPARED 'test_prepared_tab_full';");
+$node_publisher->wait_for_catchup('sub');
+
+$result = $node_subscriber->safe_psql('postgres',
+    "SELECT count(*) FROM tab_full;");
+is($result, q(5),
+   "prepared transactions done before altering can be replicated");
+
+done_testing();
-- 
2.43.0

From e4ec647fc5114440b1061d1376caca73c03f7936 Mon Sep 17 00:00:00 2001
From: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Date: Mon, 8 Apr 2024 12:39:12 +0000
Subject: [PATCH 3/4] Abort prepared transactions while altering two_phase to
 false

---
 src/backend/access/transam/twophase.c         | 19 +++++-----
 src/backend/commands/subscriptioncmds.c       | 27 +++++++++++---
 src/include/access/twophase.h                 |  3 +-
 src/test/subscription/t/099_twophase_added.pl | 35 +++++++++++++++++++
 4 files changed, 68 insertions(+), 16 deletions(-)

diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index 2148daba3c..e18e80cf4e 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -2678,13 +2678,13 @@ checkGid(char *gid, Oid subid)
 }
 
 /*
- * LookupGXactBySubid
- *		Check if the prepared transaction done by apply worker exists.
+ * GetGidListBySubid
+ *      Get a list of GIDs which is PREPARE'd by the given subscription.
  */
-bool
-LookupGXactBySubid(Oid subid)
+List *
+GetGidListBySubid(Oid subid)
 {
-	bool		found = false;
+	List *list = NIL;
 
 	LWLockAcquire(TwoPhaseStateLock, LW_SHARED);
 	for (int i = 0; i < TwoPhaseState->numPrepXacts; i++)
@@ -2693,11 +2693,10 @@ LookupGXactBySubid(Oid subid)
 
 		/* Ignore not-yet-valid GIDs. */
 		if (gxact->valid && checkGid(gxact->gid, subid))
-		{
-			found = true;
-			break;
-		}
+			list = lappend(list, pstrdup(gxact->gid));
+
 	}
 	LWLockRelease(TwoPhaseStateLock);
-	return found;
+
+	return list;
 }
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index 955d5e4899..b1c00e36db 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -1142,6 +1142,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 				/* XXX */
 				if (IsSet(opts.specified_opts, SUBOPT_TWOPHASE_COMMIT))
 				{
+					List *prepared_xacts = NIL;
+
 					/*
 					 * two_phase can be only changed for disabled
 					 * subscriptions
@@ -1158,13 +1160,28 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 					 */
 					logicalrep_workers_stop(subid);
 
-					/* Check whether the number of prepared transactions */
+					/*
+					 * If two phase was enabled, there is a possibility the
+					 * transactions has already been PREPARE'd.
+					 */
 					if (!opts.twophase &&
 						form->subtwophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
-						LookupGXactBySubid(subid))
-						ereport(ERROR,
-								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-								 errmsg("cannot disable two_phase when uncommitted prepared transactions present")));
+						(prepared_xacts = GetGidListBySubid(subid)) != NIL)
+					{
+						ListCell	*cell;
+
+						/* Must not be in the transaction */
+						PreventInTransactionBlock(isTopLevel,
+												  "ALTER SUBSCRIPTION ... SET (two_phase = ...)");
+
+						/* Abort all listed transactions */
+						foreach(cell, prepared_xacts)
+						{
+							FinishPreparedTransaction((char *) lfirst(cell),
+													  false);
+							prepared_xacts = list_delete_cell(prepared_xacts, cell);
+						}
+					}
 
 					/* Change system catalog acoordingly */
 					values[Anum_pg_subscription_subtwophasestate - 1] =
diff --git a/src/include/access/twophase.h b/src/include/access/twophase.h
index dac3f27bc3..8eebfa7267 100644
--- a/src/include/access/twophase.h
+++ b/src/include/access/twophase.h
@@ -18,6 +18,7 @@
 #include "access/xlogdefs.h"
 #include "datatype/timestamp.h"
 #include "storage/lock.h"
+#include "nodes/pg_list.h"
 
 /*
  * GlobalTransactionData is defined in twophase.c; other places have no
@@ -63,6 +64,6 @@ extern void restoreTwoPhaseData(void);
 extern bool LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 						TimestampTz origin_prepare_timestamp);
 
-extern bool LookupGXactBySubid(Oid subid);
+extern List *GetGidListBySubid(Oid subid);
 
 #endif							/* TWOPHASE_H */
diff --git a/src/test/subscription/t/099_twophase_added.pl b/src/test/subscription/t/099_twophase_added.pl
index c13a37675a..a8135b671c 100644
--- a/src/test/subscription/t/099_twophase_added.pl
+++ b/src/test/subscription/t/099_twophase_added.pl
@@ -69,4 +69,39 @@ $result = $node_subscriber->safe_psql('postgres',
 is($result, q(5),
    "prepared transactions done before altering can be replicated");
 
+######
+# Check the case that prepared transactions exist on subscriber node
+######
+
+$node_publisher->safe_psql(
+	'postgres', "
+	BEGIN;
+	INSERT INTO tab_full VALUES (generate_series(6, 10));
+	PREPARE TRANSACTION 'test_prepared_tab_full';");
+
+$node_publisher->wait_for_catchup('sub');
+
+$result = $node_subscriber->safe_psql('postgres',
+    "SELECT count(*) FROM pg_prepared_xacts;");
+is($result, q(1), "transaction has been prepared on subscriber");
+
+$node_subscriber->safe_psql(
+    'postgres', "
+    ALTER SUBSCRIPTION sub DISABLE;
+    ALTER SUBSCRIPTION sub SET (two_phase = off);
+    ALTER SUBSCRIPTION sub ENABLE;");
+
+$result = $node_subscriber->safe_psql('postgres',
+    "SELECT count(*) FROM pg_prepared_xacts;");
+is($result, q(0), "prepared transaction done by worker is aborted");
+
+$node_publisher->safe_psql( 'postgres',
+    "COMMIT PREPARED 'test_prepared_tab_full';");
+$node_publisher->wait_for_catchup('sub');
+
+$result = $node_subscriber->safe_psql('postgres',
+    "SELECT count(10) FROM tab_full;");
+is($result, q(10),
+   "prepared transactions on publisher can be replicated");
+
 done_testing();
-- 
2.43.0

From 7588a8ddfdce6193c6bfaf43ab5a09c18ed4bc8a Mon Sep 17 00:00:00 2001
From: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Date: Fri, 19 Apr 2024 11:03:19 +0000
Subject: [PATCH 4/4] Add force_alter option

---
 src/backend/commands/subscriptioncmds.c       | 37 ++++++++++++++++++-
 src/test/regress/expected/subscription.out    |  3 ++
 src/test/regress/sql/subscription.sql         |  3 ++
 src/test/subscription/t/099_twophase_added.pl | 23 +++++++++---
 4 files changed, 59 insertions(+), 7 deletions(-)

diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index b1c00e36db..e38d808d32 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -72,6 +72,7 @@
 #define SUBOPT_RUN_AS_OWNER			0x00001000
 #define SUBOPT_LSN					0x00002000
 #define SUBOPT_ORIGIN				0x00004000
+#define SUBOPT_FORCE_ALTER			0x00008000
 
 /* check if the 'val' has 'bits' set */
 #define IsSet(val, bits)  (((val) & (bits)) == (bits))
@@ -98,6 +99,7 @@ typedef struct SubOpts
 	bool		runasowner;
 	char	   *origin;
 	XLogRecPtr	lsn;
+	bool		twophase_force;
 } SubOpts;
 
 static List *fetch_table_list(WalReceiverConn *wrconn, List *publications);
@@ -158,6 +160,8 @@ parse_subscription_options(ParseState *pstate, List *stmt_options,
 		opts->runasowner = false;
 	if (IsSet(supported_opts, SUBOPT_ORIGIN))
 		opts->origin = pstrdup(LOGICALREP_ORIGIN_ANY);
+	if (IsSet(supported_opts, SUBOPT_FORCE_ALTER))
+		opts->twophase_force = false;
 
 	/* Parse options */
 	foreach(lc, stmt_options)
@@ -354,6 +358,15 @@ parse_subscription_options(ParseState *pstate, List *stmt_options,
 			opts->specified_opts |= SUBOPT_LSN;
 			opts->lsn = lsn;
 		}
+		else if (IsSet(supported_opts, SUBOPT_FORCE_ALTER) &&
+				 strcmp(defel->defname, "force_alter") == 0)
+		{
+			if (IsSet(opts->specified_opts, SUBOPT_FORCE_ALTER))
+				errorConflictingDefElem(defel, pstate);
+
+			opts->specified_opts |= SUBOPT_FORCE_ALTER;
+			opts->twophase_force = defGetBoolean(defel);
+		}
 		else
 			ereport(ERROR,
 					(errcode(ERRCODE_SYNTAX_ERROR),
@@ -1134,7 +1147,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 								  SUBOPT_STREAMING | SUBOPT_TWOPHASE_COMMIT |
 								  SUBOPT_DISABLE_ON_ERR |
 								  SUBOPT_PASSWORD_REQUIRED |
-								  SUBOPT_RUN_AS_OWNER | SUBOPT_ORIGIN);
+								  SUBOPT_RUN_AS_OWNER | SUBOPT_ORIGIN |
+								  SUBOPT_FORCE_ALTER);
 
 				parse_subscription_options(pstate, stmt->options,
 										   supported_opts, &opts);
@@ -1170,6 +1184,16 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 					{
 						ListCell	*cell;
 
+						/*
+						 * Abort prepared transactions if force option is also
+						 * specified. Otherwise raise an ERROR.
+						 */
+						if (!opts.twophase_force)
+							ereport(ERROR,
+									(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+									 errmsg("cannot alter %s when there are prepared transactions",
+											"two_phase = false")));
+
 						/* Must not be in the transaction */
 						PreventInTransactionBlock(isTopLevel,
 												  "ALTER SUBSCRIPTION ... SET (two_phase = ...)");
@@ -1179,8 +1203,9 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 						{
 							FinishPreparedTransaction((char *) lfirst(cell),
 													  false);
-							prepared_xacts = list_delete_cell(prepared_xacts, cell);
 						}
+
+						list_free(prepared_xacts);
 					}
 
 					/* Change system catalog acoordingly */
@@ -1272,6 +1297,14 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 					replaces[Anum_pg_subscription_suborigin - 1] = true;
 				}
 
+				/* force_alter cannot be used standalone */
+				if (IsSet(opts.specified_opts, SUBOPT_FORCE_ALTER) &&
+					!IsSet(opts.specified_opts, SUBOPT_TWOPHASE_COMMIT))
+					ereport(ERROR,
+							(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+							 errmsg("%s must be specified with %s",
+									"force_alter", "two_phase")));
+
 				update_tuple = true;
 				break;
 			}
diff --git a/src/test/regress/expected/subscription.out b/src/test/regress/expected/subscription.out
index 51c466f42e..946f3f6721 100644
--- a/src/test/regress/expected/subscription.out
+++ b/src/test/regress/expected/subscription.out
@@ -370,6 +370,9 @@ ERROR:  two_phase requires a Boolean value
 CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUBLICATION testpub WITH (connect = false, two_phase = true);
 WARNING:  subscription was created, but is not connected
 HINT:  To initiate replication, you must manually create the replication slot, enable the subscription, and refresh the subscription.
+-- fail - force_alter cannot be set alone
+ALTER SUBSCRIPTION regress_testsub SET (force_alter = true);
+ERROR:  force_alter must be specified with two_phase
 \dRs+
                                                                                                            List of subscriptions
       Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Synchronous commit |          Conninfo           | Skip LSN 
diff --git a/src/test/regress/sql/subscription.sql b/src/test/regress/sql/subscription.sql
index b7764c1074..2f04675980 100644
--- a/src/test/regress/sql/subscription.sql
+++ b/src/test/regress/sql/subscription.sql
@@ -255,6 +255,9 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 -- now it works
 CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUBLICATION testpub WITH (connect = false, two_phase = true);
 
+-- fail - force_alter cannot be set alone
+ALTER SUBSCRIPTION regress_testsub SET (force_alter = true);
+
 \dRs+
 -- We can alter streaming when two_phase enabled
 ALTER SUBSCRIPTION regress_testsub SET (streaming = true);
diff --git a/src/test/subscription/t/099_twophase_added.pl b/src/test/subscription/t/099_twophase_added.pl
index a8135b671c..7c73a58f2a 100644
--- a/src/test/subscription/t/099_twophase_added.pl
+++ b/src/test/subscription/t/099_twophase_added.pl
@@ -85,16 +85,29 @@ $result = $node_subscriber->safe_psql('postgres',
     "SELECT count(*) FROM pg_prepared_xacts;");
 is($result, q(1), "transaction has been prepared on subscriber");
 
-$node_subscriber->safe_psql(
-    'postgres', "
-    ALTER SUBSCRIPTION sub DISABLE;
-    ALTER SUBSCRIPTION sub SET (two_phase = off);
-    ALTER SUBSCRIPTION sub ENABLE;");
+$node_subscriber->safe_psql('postgres', "ALTER SUBSCRIPTION sub DISABLE;");
+
+my $stdout;
+my $stderr;
+
+($result, $stdout, $stderr) = $node_subscriber->psql(
+	'postgres', "ALTER SUBSCRIPTION sub SET (two_phase = off);");
+ok($stderr =~ /cannot alter two_phase = false when there are prepared transactions/,
+	'ALTER SUBSCRIPTION failed');
+
+$result = $node_subscriber->safe_psql('postgres',
+    "SELECT count(*) FROM pg_prepared_xacts;");
+is($result, q(1), "prepared transaction still exits");
+
+$node_subscriber->safe_psql('postgres',
+    "ALTER SUBSCRIPTION sub SET (two_phase = off, force_alter = on);");
 
 $result = $node_subscriber->safe_psql('postgres',
     "SELECT count(*) FROM pg_prepared_xacts;");
 is($result, q(0), "prepared transaction done by worker is aborted");
 
+$node_subscriber->safe_psql('postgres', "ALTER SUBSCRIPTION sub ENABLE;");
+
 $node_publisher->safe_psql( 'postgres',
     "COMMIT PREPARED 'test_prepared_tab_full';");
 $node_publisher->wait_for_catchup('sub');
-- 
2.43.0

From d4bb208e621c0f47500fd1b4542a5c10ebd2ec59 Mon Sep 17 00:00:00 2001
From: Ajin Cherian <ajinc@fast.au.fujitsu.com>
Date: Fri, 5 Apr 2024 06:47:18 -0400
Subject: [PATCH v6 1/4] Allow altering of two_phase option of a SUBSCRIPTION

This patch allows user to alter two_phase option of a subscriber provided no uncommitted
prepared transactions are pending on that subscription.

Author: Cherian Ajin, Hayato Kuroda
---
 doc/src/sgml/ref/alter_subscription.sgml      | 11 +--
 src/backend/access/transam/twophase.c         | 43 ++++++++++++
 src/backend/commands/subscriptioncmds.c       | 62 +++++++++++++----
 .../libpqwalreceiver/libpqwalreceiver.c       |  7 +-
 src/backend/replication/logical/launcher.c    | 21 ++++++
 src/backend/replication/logical/worker.c      |  2 +-
 src/backend/replication/slot.c                | 19 +++++-
 src/backend/replication/walsender.c           | 20 ++++--
 src/bin/psql/tab-complete.c                   |  2 +-
 src/include/access/twophase.h                 |  3 +
 src/include/replication/slot.h                |  3 +-
 src/include/replication/walreceiver.h         |  5 +-
 src/include/replication/worker_internal.h     |  1 +
 src/test/regress/expected/subscription.out    |  5 +-
 src/test/regress/sql/subscription.sql         |  5 +-
 src/test/subscription/t/021_twophase.pl       | 67 ++++++++++++++++++-
 16 files changed, 235 insertions(+), 41 deletions(-)

diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index a78c1c3a47..e69132c39d 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -68,8 +68,9 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
   <para>
    Commands <command>ALTER SUBSCRIPTION ... REFRESH PUBLICATION</command>,
    <command>ALTER SUBSCRIPTION ... {SET|ADD|DROP} PUBLICATION ...</command>
-   with <literal>refresh</literal> option as <literal>true</literal> and
-   <command>ALTER SUBSCRIPTION ... SET (failover = on|off)</command>
+   with <literal>refresh</literal> option as <literal>true</literal>,
+   <command>ALTER SUBSCRIPTION ... SET (failover = on|off)</command> and
+   <command>ALTER SUBSCRIPTION ... SET (two_phase = on|off)</command>
    cannot be executed inside a transaction block.
 
    These commands also cannot be executed when the subscription has
@@ -228,9 +229,11 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-disable-on-error"><literal>disable_on_error</literal></link>,
       <link linkend="sql-createsubscription-params-with-password-required"><literal>password_required</literal></link>,
       <link linkend="sql-createsubscription-params-with-run-as-owner"><literal>run_as_owner</literal></link>,
-      <link linkend="sql-createsubscription-params-with-origin"><literal>origin</literal></link>, and
-      <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>.
+      <link linkend="sql-createsubscription-params-with-origin"><literal>origin</literal></link>,
+      <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>, and
+      <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>.
       Only a superuser can set <literal>password_required = false</literal>.
+      <literal>two_phase</literal> can be altered only for disabled subscription.
      </para>
 
      <para>
diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index 8090ac9fc1..495f99a357 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -2682,3 +2682,46 @@ LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 	LWLockRelease(TwoPhaseStateLock);
 	return found;
 }
+
+/*
+ * checkGid
+ */
+static bool
+checkGid(char *gid, Oid subid)
+{
+	int			ret;
+	Oid			subid_written,
+				xid;
+
+	ret = sscanf(gid, "pg_gid_%u_%u", &subid_written, &xid);
+
+	if (ret != 2 || subid != subid_written)
+		return false;
+
+	return true;
+}
+
+/*
+ * LookupGXactBySubid
+ *		Check if the prepared transaction done by apply worker exists.
+ */
+bool
+LookupGXactBySubid(Oid subid)
+{
+	bool		found = false;
+
+	LWLockAcquire(TwoPhaseStateLock, LW_SHARED);
+	for (int i = 0; i < TwoPhaseState->numPrepXacts; i++)
+	{
+		GlobalTransaction gxact = TwoPhaseState->prepXacts[i];
+
+		/* Ignore not-yet-valid GIDs. */
+		if (gxact->valid && checkGid(gxact->gid, subid))
+		{
+			found = true;
+			break;
+		}
+	}
+	LWLockRelease(TwoPhaseStateLock);
+	return found;
+}
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index e407428dbc..aa8a8e1f84 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -16,6 +16,7 @@
 
 #include "access/htup_details.h"
 #include "access/table.h"
+#include "access/twophase.h"
 #include "access/xact.h"
 #include "catalog/catalog.h"
 #include "catalog/dependency.h"
@@ -1143,7 +1144,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 			{
 				supported_opts = (SUBOPT_SLOT_NAME |
 								  SUBOPT_SYNCHRONOUS_COMMIT | SUBOPT_BINARY |
-								  SUBOPT_STREAMING | SUBOPT_DISABLE_ON_ERR |
+								  SUBOPT_STREAMING | SUBOPT_TWOPHASE_COMMIT |
+								  SUBOPT_DISABLE_ON_ERR |
 								  SUBOPT_PASSWORD_REQUIRED |
 								  SUBOPT_RUN_AS_OWNER | SUBOPT_FAILOVER |
 								  SUBOPT_ORIGIN);
@@ -1151,6 +1153,47 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 				parse_subscription_options(pstate, stmt->options,
 										   supported_opts, &opts);
 
+				/* XXX */
+				if (IsSet(opts.specified_opts, SUBOPT_TWOPHASE_COMMIT))
+				{
+					/*
+					 * two_phase can be only changed for disabled
+					 * subscriptions
+					 */
+					if (form->subenabled)
+						ereport(ERROR,
+								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+								 errmsg("cannot set %s for enabled subscription",
+										"two_phase")));
+
+					/*
+					 * Stop all the subscription workers, just in case. Workers
+					 * may still survive even if the subscription is disabled.
+					 */
+					logicalrep_workers_stop(subid);
+
+					/* Check whether the number of prepared transactions */
+					if (!opts.twophase &&
+						form->subtwophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
+						LookupGXactBySubid(subid))
+						ereport(ERROR,
+								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+								 errmsg("cannot disable two_phase when uncommitted prepared transactions present")));
+
+					/*
+					 * The changed failover option of the slot can't be rolled
+					 * back.
+					 */
+					PreventInTransactionBlock(isTopLevel, "ALTER SUBSCRIPTION ... SET (two_phase)");
+
+					/* Change system catalog acoordingly */
+					values[Anum_pg_subscription_subtwophasestate - 1] =
+						CharGetDatum(opts.twophase ?
+									 LOGICALREP_TWOPHASE_STATE_PENDING :
+									 LOGICALREP_TWOPHASE_STATE_DISABLED);
+					replaces[Anum_pg_subscription_subtwophasestate - 1] = true;
+				}
+
 				if (IsSet(opts.specified_opts, SUBOPT_SLOT_NAME))
 				{
 					/*
@@ -1505,7 +1548,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 	 * doing the database operations we won't be able to rollback altered
 	 * slot.
 	 */
-	if (replaces[Anum_pg_subscription_subfailover - 1])
+	if (replaces[Anum_pg_subscription_subtwophasestate - 1] ||
+		replaces[Anum_pg_subscription_subfailover - 1])
 	{
 		bool		must_use_password;
 		char	   *err;
@@ -1525,7 +1569,7 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 
 		PG_TRY();
 		{
-			walrcv_alter_slot(wrconn, sub->slotname, opts.failover);
+			walrcv_alter_slot(wrconn, sub->slotname, opts.twophase, opts.failover);
 		}
 		PG_FINALLY();
 		{
@@ -1562,7 +1606,6 @@ DropSubscription(DropSubscriptionStmt *stmt, bool isTopLevel)
 	char	   *subname;
 	char	   *conninfo;
 	char	   *slotname;
-	List	   *subworkers;
 	ListCell   *lc;
 	char		originname[NAMEDATALEN];
 	char	   *err = NULL;
@@ -1672,16 +1715,7 @@ DropSubscription(DropSubscriptionStmt *stmt, bool isTopLevel)
 	 * New workers won't be started because we hold an exclusive lock on the
 	 * subscription till the end of the transaction.
 	 */
-	LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
-	subworkers = logicalrep_workers_find(subid, false);
-	LWLockRelease(LogicalRepWorkerLock);
-	foreach(lc, subworkers)
-	{
-		LogicalRepWorker *w = (LogicalRepWorker *) lfirst(lc);
-
-		logicalrep_worker_stop(w->subid, w->relid);
-	}
-	list_free(subworkers);
+	logicalrep_workers_stop(subid);
 
 	/*
 	 * Remove the no-longer-useful entry in the launcher's table of apply
diff --git a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
index 3c2b1bb496..baef3bdec0 100644
--- a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
+++ b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
@@ -80,7 +80,7 @@ static char *libpqrcv_create_slot(WalReceiverConn *conn,
 								  CRSSnapshotAction snapshot_action,
 								  XLogRecPtr *lsn);
 static void libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-								bool failover);
+								bool two_phase, bool failover);
 static pid_t libpqrcv_get_backend_pid(WalReceiverConn *conn);
 static WalRcvExecResult *libpqrcv_exec(WalReceiverConn *conn,
 									   const char *query,
@@ -1121,14 +1121,15 @@ libpqrcv_create_slot(WalReceiverConn *conn, const char *slotname,
  */
 static void
 libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-					bool failover)
+					bool two_phase, bool failover)
 {
 	StringInfoData cmd;
 	PGresult   *res;
 
 	initStringInfo(&cmd);
-	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( FAILOVER %s )",
+	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( TWO_PHASE %s, FAILOVER %s )",
 					 quote_identifier(slotname),
+					 two_phase ? "true" : "false",
 					 failover ? "true" : "false");
 
 	res = libpqrcv_PQexec(conn->streamConn, cmd.data);
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 66070e9131..94b73f3085 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -623,6 +623,27 @@ logicalrep_worker_stop(Oid subid, Oid relid)
 	LWLockRelease(LogicalRepWorkerLock);
 }
 
+/*
+ * Stop all the subscription workers.
+ */
+void
+logicalrep_workers_stop(Oid subid)
+{
+	List	   *subworkers;
+	ListCell   *lc;
+
+	LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
+	subworkers = logicalrep_workers_find(subid, false);
+	LWLockRelease(LogicalRepWorkerLock);
+	foreach(lc, subworkers)
+	{
+		LogicalRepWorker *w = (LogicalRepWorker *) lfirst(lc);
+
+		logicalrep_worker_stop(w->subid, w->relid);
+	}
+	list_free(subworkers);
+}
+
 /*
  * Stop the given logical replication parallel apply worker.
  *
diff --git a/src/backend/replication/logical/worker.c b/src/backend/replication/logical/worker.c
index b5a80fe3e8..374aa22091 100644
--- a/src/backend/replication/logical/worker.c
+++ b/src/backend/replication/logical/worker.c
@@ -3911,7 +3911,7 @@ maybe_reread_subscription(void)
 	/* !slotname should never happen when enabled is true. */
 	Assert(newsub->slotname);
 
-	/* two-phase should not be altered */
+	/* two-phase should not be altered while the worker exists */
 	Assert(newsub->twophasestate == MySubscription->twophasestate);
 
 	/*
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index cebf44bb0f..621f35ab1e 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -800,8 +800,10 @@ ReplicationSlotDrop(const char *name, bool nowait)
  * Change the definition of the slot identified by the specified name.
  */
 void
-ReplicationSlotAlter(const char *name, bool failover)
+ReplicationSlotAlter(const char *name, bool two_phase, bool failover)
 {
+	bool		update_slot = false;
+
 	Assert(MyReplicationSlot == NULL);
 
 	ReplicationSlotAcquire(name, false);
@@ -844,12 +846,27 @@ ReplicationSlotAlter(const char *name, bool failover)
 				errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 				errmsg("cannot enable failover for a temporary replication slot"));
 
+	if (MyReplicationSlot->data.two_phase != two_phase)
+	{
+		SpinLockAcquire(&MyReplicationSlot->mutex);
+		MyReplicationSlot->data.two_phase = two_phase;
+		SpinLockRelease(&MyReplicationSlot->mutex);
+
+		update_slot = true;
+	}
+
+
 	if (MyReplicationSlot->data.failover != failover)
 	{
 		SpinLockAcquire(&MyReplicationSlot->mutex);
 		MyReplicationSlot->data.failover = failover;
 		SpinLockRelease(&MyReplicationSlot->mutex);
 
+		update_slot = true;
+	}
+
+	if (update_slot)
+	{
 		ReplicationSlotMarkDirty();
 		ReplicationSlotSave();
 	}
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 9bf7c67f37..c45881554b 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1411,14 +1411,25 @@ DropReplicationSlot(DropReplicationSlotCmd *cmd)
  * Process extra options given to ALTER_REPLICATION_SLOT.
  */
 static void
-ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd, bool *failover)
+ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd,
+						  bool *two_phase, bool *failover)
 {
+	bool		two_phase_given = false;
 	bool		failover_given = false;
 
 	/* Parse options */
 	foreach_ptr(DefElem, defel, cmd->options)
 	{
-		if (strcmp(defel->defname, "failover") == 0)
+		if (strcmp(defel->defname, "two_phase") == 0)
+		{
+			if (two_phase_given)
+				ereport(ERROR,
+						(errcode(ERRCODE_SYNTAX_ERROR),
+						 errmsg("conflicting or redundant options")));
+			two_phase_given = true;
+			*two_phase = defGetBoolean(defel);
+		}
+		else if (strcmp(defel->defname, "failover") == 0)
 		{
 			if (failover_given)
 				ereport(ERROR,
@@ -1438,10 +1449,11 @@ ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd, bool *failover)
 static void
 AlterReplicationSlot(AlterReplicationSlotCmd *cmd)
 {
+	bool		two_phase = false;
 	bool		failover = false;
 
-	ParseAlterReplSlotOptions(cmd, &failover);
-	ReplicationSlotAlter(cmd->slotname, failover);
+	ParseAlterReplSlotOptions(cmd, &two_phase, &failover);
+	ReplicationSlotAlter(cmd->slotname, two_phase, failover);
 }
 
 /*
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
index 6fee3160f0..5ff84301cd 100644
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -1948,7 +1948,7 @@ psql_completion(const char *text, int start, int end)
 	else if (HeadMatches("ALTER", "SUBSCRIPTION", MatchAny) && TailMatches("SET", "("))
 		COMPLETE_WITH("binary", "disable_on_error", "failover", "origin",
 					  "password_required", "run_as_owner", "slot_name",
-					  "streaming", "synchronous_commit");
+					  "streaming", "synchronous_commit", "two_phase");
 	/* ALTER SUBSCRIPTION <name> SKIP ( */
 	else if (HeadMatches("ALTER", "SUBSCRIPTION", MatchAny) && TailMatches("SKIP", "("))
 		COMPLETE_WITH("lsn");
diff --git a/src/include/access/twophase.h b/src/include/access/twophase.h
index 56248c0006..d493ed24c5 100644
--- a/src/include/access/twophase.h
+++ b/src/include/access/twophase.h
@@ -62,4 +62,7 @@ extern void PrepareRedoRemove(TransactionId xid, bool giveWarning);
 extern void restoreTwoPhaseData(void);
 extern bool LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 						TimestampTz origin_prepare_timestamp);
+
+extern bool LookupGXactBySubid(Oid subid);
+
 #endif							/* TWOPHASE_H */
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 7b937d1a0c..2fcb11418f 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -243,7 +243,8 @@ extern void ReplicationSlotCreate(const char *name, bool db_specific,
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
 extern void ReplicationSlotDropAcquired(void);
-extern void ReplicationSlotAlter(const char *name, bool failover);
+extern void ReplicationSlotAlter(const char *name, bool two_phase,
+								 bool failover);
 
 extern void ReplicationSlotAcquire(const char *name, bool nowait);
 extern void ReplicationSlotRelease(void);
diff --git a/src/include/replication/walreceiver.h b/src/include/replication/walreceiver.h
index 12f71fa99b..a443f402f5 100644
--- a/src/include/replication/walreceiver.h
+++ b/src/include/replication/walreceiver.h
@@ -377,6 +377,7 @@ typedef char *(*walrcv_create_slot_fn) (WalReceiverConn *conn,
  */
 typedef void (*walrcv_alter_slot_fn) (WalReceiverConn *conn,
 									  const char *slotname,
+									  bool two_phase,
 									  bool failover);
 
 /*
@@ -455,8 +456,8 @@ extern PGDLLIMPORT WalReceiverFunctionsType *WalReceiverFunctions;
 	WalReceiverFunctions->walrcv_send(conn, buffer, nbytes)
 #define walrcv_create_slot(conn, slotname, temporary, two_phase, failover, snapshot_action, lsn) \
 	WalReceiverFunctions->walrcv_create_slot(conn, slotname, temporary, two_phase, failover, snapshot_action, lsn)
-#define walrcv_alter_slot(conn, slotname, failover) \
-	WalReceiverFunctions->walrcv_alter_slot(conn, slotname, failover)
+#define walrcv_alter_slot(conn, slotname, two_phase, failover) \
+	WalReceiverFunctions->walrcv_alter_slot(conn, slotname, two_phase, failover)
 #define walrcv_get_backend_pid(conn) \
 	WalReceiverFunctions->walrcv_get_backend_pid(conn)
 #define walrcv_exec(conn, exec, nRetTypes, retTypes) \
diff --git a/src/include/replication/worker_internal.h b/src/include/replication/worker_internal.h
index 515aefd519..d5428263c1 100644
--- a/src/include/replication/worker_internal.h
+++ b/src/include/replication/worker_internal.h
@@ -246,6 +246,7 @@ extern bool logicalrep_worker_launch(LogicalRepWorkerType wtype,
 									 Oid userid, Oid relid,
 									 dsm_handle subworker_dsm);
 extern void logicalrep_worker_stop(Oid subid, Oid relid);
+extern void logicalrep_workers_stop(Oid subid);
 extern void logicalrep_pa_worker_stop(ParallelApplyWorkerInfo *winfo);
 extern void logicalrep_worker_wakeup(Oid subid, Oid relid);
 extern void logicalrep_worker_wakeup_ptr(LogicalRepWorker *worker);
diff --git a/src/test/regress/expected/subscription.out b/src/test/regress/expected/subscription.out
index 0f2a25cdc1..51fa4b9690 100644
--- a/src/test/regress/expected/subscription.out
+++ b/src/test/regress/expected/subscription.out
@@ -377,10 +377,7 @@ HINT:  To initiate replication, you must manually create the replication slot, e
  regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | p                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
---fail - alter of two_phase option not supported.
-ALTER SUBSCRIPTION regress_testsub SET (two_phase = false);
-ERROR:  unrecognized subscription parameter: "two_phase"
--- but can alter streaming when two_phase enabled
+-- We can alter streaming when two_phase enabled
 ALTER SUBSCRIPTION regress_testsub SET (streaming = true);
 \dRs+
                                                                                                                 List of subscriptions
diff --git a/src/test/regress/sql/subscription.sql b/src/test/regress/sql/subscription.sql
index 3e5ba4cb8c..a3886d79ca 100644
--- a/src/test/regress/sql/subscription.sql
+++ b/src/test/regress/sql/subscription.sql
@@ -256,10 +256,7 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUBLICATION testpub WITH (connect = false, two_phase = true);
 
 \dRs+
---fail - alter of two_phase option not supported.
-ALTER SUBSCRIPTION regress_testsub SET (two_phase = false);
-
--- but can alter streaming when two_phase enabled
+-- We can alter streaming when two_phase enabled
 ALTER SUBSCRIPTION regress_testsub SET (streaming = true);
 
 \dRs+
diff --git a/src/test/subscription/t/021_twophase.pl b/src/test/subscription/t/021_twophase.pl
index 9437cd4c3b..e710f3c4c0 100644
--- a/src/test/subscription/t/021_twophase.pl
+++ b/src/test/subscription/t/021_twophase.pl
@@ -367,6 +367,71 @@ $result =
   $node_subscriber->safe_psql('postgres', "SELECT count(*) FROM tab_copy;");
 is($result, qq(2), 'replicated data in subscriber table');
 
+# Disable the subscription and alter it to two_phase = false,
+# verify that the altered subscription reflects the two_phase option.
+
+# Alter subscription two_phase to false
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy DISABLE");
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = false)");
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy ENABLE");
+
+# Wait for subscription startup
+$node_subscriber->wait_for_subscription_sync($node_publisher, $appname_copy);
+
+# Make sure that the two-phase is disabled on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+       "SELECT subtwophasestate FROM pg_subscription WHERE subname = 'tap_sub_copy';"
+);
+is($result, qq(d), 'two-phase is disabled');
+
+# Now do a prepare on publisher and make sure that it is not replicated.
+$node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub");
+$node_publisher->safe_psql(
+       'postgres', qq{
+    BEGIN;
+    INSERT INTO tab_copy VALUES (100);
+    PREPARE TRANSACTION 'newgid';
+	});
+
+# Wait for the subscriber to catchup
+$node_publisher->wait_for_catchup($appname_copy);
+
+# Make sure that there is 0 prepared transaction on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT count(*) FROM pg_prepared_xacts;");
+is($result, qq(0), 'transaction is prepared on subscriber');
+
+# Now commit the insert and verify that it IS replicated
+$node_publisher->safe_psql('postgres', "COMMIT PREPARED 'newgid';");
+
+# Wait for the subscriber to catchup
+$node_publisher->wait_for_catchup($appname_copy);
+
+# Made sure that the commited transaction is replicated.
+$result =
+	$node_subscriber->safe_psql('postgres', "SELECT count(*) FROM tab_copy;");
+is($result, qq(3), 'replicated data in subscriber table');
+
+# Alter subscription two_phase to true
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy DISABLE");
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = true)");
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy ENABLE");
+
+# Wait for subscription startup
+$node_subscriber->wait_for_subscription_sync($node_publisher, $appname_copy);
+
+# Make sure that the two-phase is enabled on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT subtwophasestate FROM pg_subscription WHERE subname = 'tap_sub_copy';"
+);
+is($result, qq(e), 'two-phase is disabled');
+
 $node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub_copy;");
 $node_publisher->safe_psql('postgres', "DROP PUBLICATION tap_pub_copy;");
 
@@ -374,8 +439,6 @@ $node_publisher->safe_psql('postgres', "DROP PUBLICATION tap_pub_copy;");
 # check all the cleanup
 ###############################
 
-$node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub");
-
 $result = $node_subscriber->safe_psql('postgres',
 	"SELECT count(*) FROM pg_subscription");
 is($result, qq(0), 'check subscription was dropped on subscriber');
-- 
2.43.0

From 458bdbfeabae2e22dae84386a8b8e54126d101a3 Mon Sep 17 00:00:00 2001
From: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Date: Wed, 17 Apr 2024 06:18:23 +0000
Subject: [PATCH v6 2/4] Alter slot option two_phase only when altering true to
 false

---
 doc/src/sgml/ref/alter_subscription.sgml      |  2 +-
 src/backend/commands/subscriptioncmds.c       | 23 +++++-
 .../libpqwalreceiver/libpqwalreceiver.c       | 21 ++++--
 src/include/replication/walreceiver.h         |  8 +--
 src/test/subscription/meson.build             |  1 +
 src/test/subscription/t/099_twophase_added.pl | 72 +++++++++++++++++++
 6 files changed, 114 insertions(+), 13 deletions(-)
 create mode 100644 src/test/subscription/t/099_twophase_added.pl

diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index e69132c39d..e54aa1b128 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -70,7 +70,7 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
    <command>ALTER SUBSCRIPTION ... {SET|ADD|DROP} PUBLICATION ...</command>
    with <literal>refresh</literal> option as <literal>true</literal>,
    <command>ALTER SUBSCRIPTION ... SET (failover = on|off)</command> and
-   <command>ALTER SUBSCRIPTION ... SET (two_phase = on|off)</command>
+   <command>ALTER SUBSCRIPTION ... SET (two_phase = off)</command>
    cannot be executed inside a transaction block.
 
    These commands also cannot be executed when the subscription has
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index aa8a8e1f84..b02e21f535 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -1184,7 +1184,9 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 					 * The changed failover option of the slot can't be rolled
 					 * back.
 					 */
-					PreventInTransactionBlock(isTopLevel, "ALTER SUBSCRIPTION ... SET (two_phase)");
+					if (!opts.twophase)
+						PreventInTransactionBlock(isTopLevel,
+												  "ALTER SUBSCRIPTION ... SET (two_phase = off)");
 
 					/* Change system catalog acoordingly */
 					values[Anum_pg_subscription_subtwophasestate - 1] =
@@ -1554,6 +1556,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 		bool		must_use_password;
 		char	   *err;
 		WalReceiverConn *wrconn;
+		bool		two_phase_needs_to_be_updated;
+		bool		failover_needs_to_be_updated;
 
 		/* Load the library providing us libpq calls. */
 		load_file("libpqwalreceiver", false);
@@ -1567,9 +1571,24 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 					(errcode(ERRCODE_CONNECTION_FAILURE),
 					 errmsg("could not connect to the publisher: %s", err)));
 
+		/*
+		 * Consider which slot option must be altered.
+		 *
+		 * We must alter the failover option whenever subfailover is updated.
+		 * Two_phase, however, is altered only when changing true to false.
+		 */
+		two_phase_needs_to_be_updated =
+						(replaces[Anum_pg_subscription_subtwophasestate - 1] &&
+						 !opts.twophase);
+		failover_needs_to_be_updated =
+								replaces[Anum_pg_subscription_subfailover - 1];
+
 		PG_TRY();
 		{
-			walrcv_alter_slot(wrconn, sub->slotname, opts.twophase, opts.failover);
+			if (two_phase_needs_to_be_updated || failover_needs_to_be_updated)
+				walrcv_alter_slot(wrconn, sub->slotname,
+								  two_phase_needs_to_be_updated ? &opts.twophase : NULL,
+								  failover_needs_to_be_updated ? &opts.failover : NULL);
 		}
 		PG_FINALLY();
 		{
diff --git a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
index baef3bdec0..546b599848 100644
--- a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
+++ b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
@@ -80,7 +80,7 @@ static char *libpqrcv_create_slot(WalReceiverConn *conn,
 								  CRSSnapshotAction snapshot_action,
 								  XLogRecPtr *lsn);
 static void libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-								bool two_phase, bool failover);
+								const bool *two_phase, const bool *failover);
 static pid_t libpqrcv_get_backend_pid(WalReceiverConn *conn);
 static WalRcvExecResult *libpqrcv_exec(WalReceiverConn *conn,
 									   const char *query,
@@ -1121,16 +1121,25 @@ libpqrcv_create_slot(WalReceiverConn *conn, const char *slotname,
  */
 static void
 libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-					bool two_phase, bool failover)
+					const bool *two_phase, const bool *failover)
 {
 	StringInfoData cmd;
 	PGresult   *res;
 
 	initStringInfo(&cmd);
-	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( TWO_PHASE %s, FAILOVER %s )",
-					 quote_identifier(slotname),
-					 two_phase ? "true" : "false",
-					 failover ? "true" : "false");
+	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( ",
+					 quote_identifier(slotname));
+
+	if (two_phase)
+		appendStringInfo(&cmd, "TWO_PHASE %s%s ",
+						 (*two_phase) ? "true" : "false",
+						 failover ? ", " : "");
+
+	if (failover)
+		appendStringInfo(&cmd, "FAILOVER %s ",
+						 (*failover) ? "true" : "false");
+
+	appendStringInfoString(&cmd, ");");
 
 	res = libpqrcv_PQexec(conn->streamConn, cmd.data);
 	pfree(cmd.data);
diff --git a/src/include/replication/walreceiver.h b/src/include/replication/walreceiver.h
index a443f402f5..f30637aa4a 100644
--- a/src/include/replication/walreceiver.h
+++ b/src/include/replication/walreceiver.h
@@ -372,13 +372,13 @@ typedef char *(*walrcv_create_slot_fn) (WalReceiverConn *conn,
 /*
  * walrcv_alter_slot_fn
  *
- * Change the definition of a replication slot. Currently, it only supports
- * changing the failover property of the slot.
+ * Change the definition of a replication slot. Currently, it supports
+ * changing the two_phase and the failover property of the slot.
  */
 typedef void (*walrcv_alter_slot_fn) (WalReceiverConn *conn,
 									  const char *slotname,
-									  bool two_phase,
-									  bool failover);
+									  const bool *two_phase,
+									  const bool *failover);
 
 /*
  * walrcv_get_backend_pid_fn
diff --git a/src/test/subscription/meson.build b/src/test/subscription/meson.build
index c591cd7d61..b4bd522c3d 100644
--- a/src/test/subscription/meson.build
+++ b/src/test/subscription/meson.build
@@ -40,6 +40,7 @@ tests += {
       't/031_column_list.pl',
       't/032_subscribe_use_index.pl',
       't/033_run_as_table_owner.pl',
+      't/099_twophase_added.pl',
       't/100_bugs.pl',
     ],
   },
diff --git a/src/test/subscription/t/099_twophase_added.pl b/src/test/subscription/t/099_twophase_added.pl
new file mode 100644
index 0000000000..c13a37675a
--- /dev/null
+++ b/src/test/subscription/t/099_twophase_added.pl
@@ -0,0 +1,72 @@
+# Copyright (c) 2021-2024, PostgreSQL Global Development Group
+
+# Additional tests for altering two_phase option
+use strict;
+use warnings FATAL => 'all';
+use PostgreSQL::Test::Cluster;
+use PostgreSQL::Test::Utils;
+use Test::More;
+
+# Initialize publisher node
+my $node_publisher = PostgreSQL::Test::Cluster->new('publisher');
+$node_publisher->init(allows_streaming => 'logical');
+$node_publisher->append_conf('postgresql.conf',
+	qq(max_prepared_transactions = 10));
+$node_publisher->start;
+
+# Create subscriber node
+my $node_subscriber = PostgreSQL::Test::Cluster->new('subscriber');
+$node_subscriber->init;
+$node_subscriber->append_conf('postgresql.conf',
+	qq(max_prepared_transactions = 10));
+$node_subscriber->start;
+
+# Define pre-existing tables on both nodes
+$node_publisher->safe_psql('postgres',
+    "CREATE TABLE tab_full (a int PRIMARY KEY);");
+$node_subscriber->safe_psql('postgres',
+	"CREATE TABLE tab_full (a int PRIMARY KEY)");
+
+# Setup logical replication, with two_phase = off
+my $publisher_connstr = $node_publisher->connstr . ' dbname=postgres';
+$node_publisher->safe_psql('postgres',
+	"CREATE PUBLICATION pub FOR ALL TABLES");
+
+$node_subscriber->safe_psql(
+	'postgres', "
+	CREATE SUBSCRIPTION sub
+	CONNECTION '$publisher_connstr' PUBLICATION pub
+	WITH (two_phase = off, copy_data = off)");
+
+######
+# Check the case that prepared transactions exist on publisher node
+######
+
+$node_publisher->safe_psql(
+	'postgres', "
+	BEGIN;
+	INSERT INTO tab_full VALUES (generate_series(1, 5));
+	PREPARE TRANSACTION 'test_prepared_tab_full';");
+
+$node_publisher->wait_for_catchup('sub');
+
+my $result = $node_subscriber->safe_psql('postgres',
+    "SELECT count(*) FROM pg_prepared_xacts;");
+is($result, q(0), "transaction is not prepared on subscriber");
+
+$node_subscriber->safe_psql(
+    'postgres', "
+    ALTER SUBSCRIPTION sub DISABLE;
+    ALTER SUBSCRIPTION sub SET (two_phase = on);
+    ALTER SUBSCRIPTION sub ENABLE;");
+
+$node_publisher->safe_psql( 'postgres',
+    "COMMIT PREPARED 'test_prepared_tab_full';");
+$node_publisher->wait_for_catchup('sub');
+
+$result = $node_subscriber->safe_psql('postgres',
+    "SELECT count(*) FROM tab_full;");
+is($result, q(5),
+   "prepared transactions done before altering can be replicated");
+
+done_testing();
-- 
2.43.0

From d0c8138ccdf19dd9d4395855e5482cce496bda22 Mon Sep 17 00:00:00 2001
From: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Date: Mon, 8 Apr 2024 12:39:12 +0000
Subject: [PATCH v6 3/4] Abort prepared transactions while altering two_phase
 to false

---
 doc/src/sgml/ref/alter_subscription.sgml      |  8 ++++-
 src/backend/access/transam/twophase.c         | 19 +++++-----
 src/backend/commands/subscriptioncmds.c       | 33 +++++++++++------
 src/include/access/twophase.h                 |  3 +-
 src/test/subscription/t/099_twophase_added.pl | 35 +++++++++++++++++++
 5 files changed, 76 insertions(+), 22 deletions(-)

diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index e54aa1b128..926f560566 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -233,7 +233,6 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>, and
       <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>.
       Only a superuser can set <literal>password_required = false</literal>.
-      <literal>two_phase</literal> can be altered only for disabled subscription.
      </para>
 
      <para>
@@ -255,6 +254,13 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>
       option is enabled.
      </para>
+
+     <para>
+      <literal>two_phase</literal> can be altered only for disabled
+      subscriptions. When altering the parameter from <literal>true</literal>
+      to <literal>false</literal>, the backend process checks prepared
+      transactions done by the logical replication worker and aborts them.
+     </para>
     </listitem>
    </varlistentry>
 
diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index 495f99a357..9121195725 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -2702,13 +2702,13 @@ checkGid(char *gid, Oid subid)
 }
 
 /*
- * LookupGXactBySubid
- *		Check if the prepared transaction done by apply worker exists.
+ * GetGidListBySubid
+ *      Get a list of GIDs which is PREPARE'd by the given subscription.
  */
-bool
-LookupGXactBySubid(Oid subid)
+List *
+GetGidListBySubid(Oid subid)
 {
-	bool		found = false;
+	List *list = NIL;
 
 	LWLockAcquire(TwoPhaseStateLock, LW_SHARED);
 	for (int i = 0; i < TwoPhaseState->numPrepXacts; i++)
@@ -2717,11 +2717,10 @@ LookupGXactBySubid(Oid subid)
 
 		/* Ignore not-yet-valid GIDs. */
 		if (gxact->valid && checkGid(gxact->gid, subid))
-		{
-			found = true;
-			break;
-		}
+			list = lappend(list, pstrdup(gxact->gid));
+
 	}
 	LWLockRelease(TwoPhaseStateLock);
-	return found;
+
+	return list;
 }
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index b02e21f535..8a36558b2c 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -1156,6 +1156,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 				/* XXX */
 				if (IsSet(opts.specified_opts, SUBOPT_TWOPHASE_COMMIT))
 				{
+					List *prepared_xacts = NIL;
+
 					/*
 					 * two_phase can be only changed for disabled
 					 * subscriptions
@@ -1172,22 +1174,33 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 					 */
 					logicalrep_workers_stop(subid);
 
-					/* Check whether the number of prepared transactions */
-					if (!opts.twophase &&
-						form->subtwophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
-						LookupGXactBySubid(subid))
-						ereport(ERROR,
-								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-								 errmsg("cannot disable two_phase when uncommitted prepared transactions present")));
-
 					/*
-					 * The changed failover option of the slot can't be rolled
-					 * back.
+					 * If two phase was enabled, there is a possibility the
+					 * transactions has already been PREPARE'd.
 					 */
 					if (!opts.twophase)
+					{
+						/*
+						 * The changed failover option of the slot can't be rolled
+						 * back.
+						 */
 						PreventInTransactionBlock(isTopLevel,
 												  "ALTER SUBSCRIPTION ... SET (two_phase = off)");
 
+						if (sub->twophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
+							(prepared_xacts = GetGidListBySubid(subid)) != NIL)
+						{
+							ListCell	*cell;
+
+							/* Abort all listed transactions */
+							foreach(cell, prepared_xacts)
+								FinishPreparedTransaction((char *) lfirst(cell),
+														  false);
+
+							list_free(prepared_xacts);
+						}
+					}
+
 					/* Change system catalog acoordingly */
 					values[Anum_pg_subscription_subtwophasestate - 1] =
 						CharGetDatum(opts.twophase ?
diff --git a/src/include/access/twophase.h b/src/include/access/twophase.h
index d493ed24c5..95770bbd69 100644
--- a/src/include/access/twophase.h
+++ b/src/include/access/twophase.h
@@ -18,6 +18,7 @@
 #include "access/xlogdefs.h"
 #include "datatype/timestamp.h"
 #include "storage/lock.h"
+#include "nodes/pg_list.h"
 
 /*
  * GlobalTransactionData is defined in twophase.c; other places have no
@@ -63,6 +64,6 @@ extern void restoreTwoPhaseData(void);
 extern bool LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 						TimestampTz origin_prepare_timestamp);
 
-extern bool LookupGXactBySubid(Oid subid);
+extern List *GetGidListBySubid(Oid subid);
 
 #endif							/* TWOPHASE_H */
diff --git a/src/test/subscription/t/099_twophase_added.pl b/src/test/subscription/t/099_twophase_added.pl
index c13a37675a..a8135b671c 100644
--- a/src/test/subscription/t/099_twophase_added.pl
+++ b/src/test/subscription/t/099_twophase_added.pl
@@ -69,4 +69,39 @@ $result = $node_subscriber->safe_psql('postgres',
 is($result, q(5),
    "prepared transactions done before altering can be replicated");
 
+######
+# Check the case that prepared transactions exist on subscriber node
+######
+
+$node_publisher->safe_psql(
+	'postgres', "
+	BEGIN;
+	INSERT INTO tab_full VALUES (generate_series(6, 10));
+	PREPARE TRANSACTION 'test_prepared_tab_full';");
+
+$node_publisher->wait_for_catchup('sub');
+
+$result = $node_subscriber->safe_psql('postgres',
+    "SELECT count(*) FROM pg_prepared_xacts;");
+is($result, q(1), "transaction has been prepared on subscriber");
+
+$node_subscriber->safe_psql(
+    'postgres', "
+    ALTER SUBSCRIPTION sub DISABLE;
+    ALTER SUBSCRIPTION sub SET (two_phase = off);
+    ALTER SUBSCRIPTION sub ENABLE;");
+
+$result = $node_subscriber->safe_psql('postgres',
+    "SELECT count(*) FROM pg_prepared_xacts;");
+is($result, q(0), "prepared transaction done by worker is aborted");
+
+$node_publisher->safe_psql( 'postgres',
+    "COMMIT PREPARED 'test_prepared_tab_full';");
+$node_publisher->wait_for_catchup('sub');
+
+$result = $node_subscriber->safe_psql('postgres',
+    "SELECT count(10) FROM tab_full;");
+is($result, q(10),
+   "prepared transactions on publisher can be replicated");
+
 done_testing();
-- 
2.43.0

From 79b7d98f71c6bf6676ce868d16f8965709a4251a Mon Sep 17 00:00:00 2001
From: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Date: Fri, 19 Apr 2024 11:03:19 +0000
Subject: [PATCH v6 4/4] Add force_alter option

---
 doc/src/sgml/ref/alter_subscription.sgml      |  9 +++--
 src/backend/commands/subscriptioncmds.c       | 33 ++++++++++++++++++-
 src/test/regress/expected/subscription.out    |  3 ++
 src/test/regress/sql/subscription.sql         |  3 ++
 src/test/subscription/t/099_twophase_added.pl | 23 ++++++++++---
 5 files changed, 62 insertions(+), 9 deletions(-)

diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index 926f560566..e6228490a8 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -257,9 +257,12 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
 
      <para>
       <literal>two_phase</literal> can be altered only for disabled
-      subscriptions. When altering the parameter from <literal>true</literal>
-      to <literal>false</literal>, the backend process checks prepared
-      transactions done by the logical replication worker and aborts them.
+      subscriptions. Altering the parameter from <literal>true</literal>
+      to <literal>false</literal> will be failed when there are prepared
+      transactions done by the logical replication worker. If you want to alter
+      the parameter forcibly in this case, <literal>force_alter</literal>
+      option must be set to <literal>true</literal> at the same time. If
+      specified, the backend process aborts prepared transactions.
      </para>
     </listitem>
    </varlistentry>
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index 8a36558b2c..7ea4e85595 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -73,6 +73,7 @@
 #define SUBOPT_FAILOVER				0x00002000
 #define SUBOPT_LSN					0x00004000
 #define SUBOPT_ORIGIN				0x00008000
+#define SUBOPT_FORCE_ALTER			0x00010000
 
 /* check if the 'val' has 'bits' set */
 #define IsSet(val, bits)  (((val) & (bits)) == (bits))
@@ -100,6 +101,7 @@ typedef struct SubOpts
 	bool		failover;
 	char	   *origin;
 	XLogRecPtr	lsn;
+	bool		twophase_force;
 } SubOpts;
 
 static List *fetch_table_list(WalReceiverConn *wrconn, List *publications);
@@ -162,6 +164,8 @@ parse_subscription_options(ParseState *pstate, List *stmt_options,
 		opts->failover = false;
 	if (IsSet(supported_opts, SUBOPT_ORIGIN))
 		opts->origin = pstrdup(LOGICALREP_ORIGIN_ANY);
+	if (IsSet(supported_opts, SUBOPT_FORCE_ALTER))
+		opts->twophase_force = false;
 
 	/* Parse options */
 	foreach(lc, stmt_options)
@@ -367,6 +371,15 @@ parse_subscription_options(ParseState *pstate, List *stmt_options,
 			opts->specified_opts |= SUBOPT_LSN;
 			opts->lsn = lsn;
 		}
+		else if (IsSet(supported_opts, SUBOPT_FORCE_ALTER) &&
+				 strcmp(defel->defname, "force_alter") == 0)
+		{
+			if (IsSet(opts->specified_opts, SUBOPT_FORCE_ALTER))
+				errorConflictingDefElem(defel, pstate);
+
+			opts->specified_opts |= SUBOPT_FORCE_ALTER;
+			opts->twophase_force = defGetBoolean(defel);
+		}
 		else
 			ereport(ERROR,
 					(errcode(ERRCODE_SYNTAX_ERROR),
@@ -1148,7 +1161,7 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 								  SUBOPT_DISABLE_ON_ERR |
 								  SUBOPT_PASSWORD_REQUIRED |
 								  SUBOPT_RUN_AS_OWNER | SUBOPT_FAILOVER |
-								  SUBOPT_ORIGIN);
+								  SUBOPT_ORIGIN | SUBOPT_FORCE_ALTER);
 
 				parse_subscription_options(pstate, stmt->options,
 										   supported_opts, &opts);
@@ -1192,6 +1205,16 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 						{
 							ListCell	*cell;
 
+							/*
+							 * Abort prepared transactions if force option is also
+							 * specified. Otherwise raise an ERROR.
+							 */
+							if (!opts.twophase_force)
+								ereport(ERROR,
+										(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+										 errmsg("cannot alter %s when there are prepared transactions",
+												"two_phase = false")));
+
 							/* Abort all listed transactions */
 							foreach(cell, prepared_xacts)
 								FinishPreparedTransaction((char *) lfirst(cell),
@@ -1321,6 +1344,14 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 					replaces[Anum_pg_subscription_suborigin - 1] = true;
 				}
 
+				/* force_alter cannot be used standalone */
+				if (IsSet(opts.specified_opts, SUBOPT_FORCE_ALTER) &&
+					!IsSet(opts.specified_opts, SUBOPT_TWOPHASE_COMMIT))
+					ereport(ERROR,
+							(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+							 errmsg("%s must be specified with %s",
+									"force_alter", "two_phase")));
+
 				update_tuple = true;
 				break;
 			}
diff --git a/src/test/regress/expected/subscription.out b/src/test/regress/expected/subscription.out
index 51fa4b9690..f607045b28 100644
--- a/src/test/regress/expected/subscription.out
+++ b/src/test/regress/expected/subscription.out
@@ -370,6 +370,9 @@ ERROR:  two_phase requires a Boolean value
 CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUBLICATION testpub WITH (connect = false, two_phase = true);
 WARNING:  subscription was created, but is not connected
 HINT:  To initiate replication, you must manually create the replication slot, enable the subscription, and refresh the subscription.
+-- fail - force_alter cannot be set alone
+ALTER SUBSCRIPTION regress_testsub SET (force_alter = true);
+ERROR:  force_alter must be specified with two_phase
 \dRs+
                                                                                                                 List of subscriptions
       Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
diff --git a/src/test/regress/sql/subscription.sql b/src/test/regress/sql/subscription.sql
index a3886d79ca..80ab4dd9bc 100644
--- a/src/test/regress/sql/subscription.sql
+++ b/src/test/regress/sql/subscription.sql
@@ -255,6 +255,9 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 -- now it works
 CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUBLICATION testpub WITH (connect = false, two_phase = true);
 
+-- fail - force_alter cannot be set alone
+ALTER SUBSCRIPTION regress_testsub SET (force_alter = true);
+
 \dRs+
 -- We can alter streaming when two_phase enabled
 ALTER SUBSCRIPTION regress_testsub SET (streaming = true);
diff --git a/src/test/subscription/t/099_twophase_added.pl b/src/test/subscription/t/099_twophase_added.pl
index a8135b671c..7c73a58f2a 100644
--- a/src/test/subscription/t/099_twophase_added.pl
+++ b/src/test/subscription/t/099_twophase_added.pl
@@ -85,16 +85,29 @@ $result = $node_subscriber->safe_psql('postgres',
     "SELECT count(*) FROM pg_prepared_xacts;");
 is($result, q(1), "transaction has been prepared on subscriber");
 
-$node_subscriber->safe_psql(
-    'postgres', "
-    ALTER SUBSCRIPTION sub DISABLE;
-    ALTER SUBSCRIPTION sub SET (two_phase = off);
-    ALTER SUBSCRIPTION sub ENABLE;");
+$node_subscriber->safe_psql('postgres', "ALTER SUBSCRIPTION sub DISABLE;");
+
+my $stdout;
+my $stderr;
+
+($result, $stdout, $stderr) = $node_subscriber->psql(
+	'postgres', "ALTER SUBSCRIPTION sub SET (two_phase = off);");
+ok($stderr =~ /cannot alter two_phase = false when there are prepared transactions/,
+	'ALTER SUBSCRIPTION failed');
+
+$result = $node_subscriber->safe_psql('postgres',
+    "SELECT count(*) FROM pg_prepared_xacts;");
+is($result, q(1), "prepared transaction still exits");
+
+$node_subscriber->safe_psql('postgres',
+    "ALTER SUBSCRIPTION sub SET (two_phase = off, force_alter = on);");
 
 $result = $node_subscriber->safe_psql('postgres',
     "SELECT count(*) FROM pg_prepared_xacts;");
 is($result, q(0), "prepared transaction done by worker is aborted");
 
+$node_subscriber->safe_psql('postgres', "ALTER SUBSCRIPTION sub ENABLE;");
+
 $node_publisher->safe_psql( 'postgres',
     "COMMIT PREPARED 'test_prepared_tab_full';");
 $node_publisher->wait_for_catchup('sub');
-- 
2.43.0

From e5e7a64c5521c4603490042f451228b32233a72a Mon Sep 17 00:00:00 2001
From: Ajin Cherian <ajinc@fast.au.fujitsu.com>
Date: Fri, 5 Apr 2024 06:47:18 -0400
Subject: [PATCH v7 1/4] Allow altering of two_phase option of a SUBSCRIPTION

This patch allows the user to alter the 'two_phase' option of a subscriber provided no
uncommitted prepared transactions are pending on that subscription.

Author: Cherian Ajin, Hayato Kuroda
---
 doc/src/sgml/ref/alter_subscription.sgml      | 12 ++--
 src/backend/access/transam/twophase.c         | 61 ++++++++++++++++
 src/backend/commands/subscriptioncmds.c       | 68 ++++++++++++++----
 .../libpqwalreceiver/libpqwalreceiver.c       |  9 +--
 src/backend/replication/logical/launcher.c    | 22 ++++++
 src/backend/replication/logical/worker.c      | 21 +-----
 src/backend/replication/slot.c                | 18 ++++-
 src/backend/replication/walsender.c           | 18 ++++-
 src/bin/psql/tab-complete.c                   |  2 +-
 src/include/access/twophase.h                 |  5 ++
 src/include/replication/slot.h                |  3 +-
 src/include/replication/walreceiver.h         | 11 +--
 src/include/replication/worker_internal.h     |  1 +
 src/test/regress/expected/subscription.out    |  5 +-
 src/test/regress/sql/subscription.sql         |  5 +-
 src/test/subscription/t/021_twophase.pl       | 71 ++++++++++++++++++-
 16 files changed, 269 insertions(+), 63 deletions(-)

diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index a78c1c3a47..88e9a72147 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -68,8 +68,9 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
   <para>
    Commands <command>ALTER SUBSCRIPTION ... REFRESH PUBLICATION</command>,
    <command>ALTER SUBSCRIPTION ... {SET|ADD|DROP} PUBLICATION ...</command>
-   with <literal>refresh</literal> option as <literal>true</literal> and
-   <command>ALTER SUBSCRIPTION ... SET (failover = on|off)</command>
+   with <literal>refresh</literal> option as <literal>true</literal>,
+   <command>ALTER SUBSCRIPTION ... SET (failover = on|off)</command> and
+   <command>ALTER SUBSCRIPTION ... SET (two_phase = on|off)</command>
    cannot be executed inside a transaction block.
 
    These commands also cannot be executed when the subscription has
@@ -228,9 +229,12 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-disable-on-error"><literal>disable_on_error</literal></link>,
       <link linkend="sql-createsubscription-params-with-password-required"><literal>password_required</literal></link>,
       <link linkend="sql-createsubscription-params-with-run-as-owner"><literal>run_as_owner</literal></link>,
-      <link linkend="sql-createsubscription-params-with-origin"><literal>origin</literal></link>, and
-      <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>.
+      <link linkend="sql-createsubscription-params-with-origin"><literal>origin</literal></link>,
+      <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>, and
+      <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>.
       Only a superuser can set <literal>password_required = false</literal>.
+      The <literal>two_phase</literal> parameter can only be altered when the
+      subscription is disabled.
      </para>
 
      <para>
diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index 8090ac9fc1..a67a8c48aa 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -2682,3 +2682,64 @@ LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 	LWLockRelease(TwoPhaseStateLock);
 	return found;
 }
+
+/*
+ * TwoPhaseTransactionGid
+ *		Form the prepared transaction GID for two_phase transactions.
+ *
+ * Return the GID in the supplied buffer.
+ */
+void
+TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid, int szgid)
+{
+	Assert(subid != InvalidRepOriginId);
+
+	if (!TransactionIdIsValid(xid))
+		ereport(ERROR,
+				(errcode(ERRCODE_PROTOCOL_VIOLATION),
+				 errmsg_internal("invalid two-phase transaction ID")));
+
+	snprintf(gid, szgid, "pg_gid_%u_%u", subid, xid);
+}
+
+/*
+ * IsTwoPhaseTransactionGidForSubid
+ *		Check whether the given GID is formed by TwoPhaseTransactionGid.
+ */
+static bool
+IsTwoPhaseTransactionGidForSubid(Oid subid, char *gid)
+{
+	int				ret;
+	Oid				subid_written;
+	TransactionId	xid;
+
+	ret = sscanf(gid, "pg_gid_%u_%u", &subid_written, &xid);
+
+	return (ret == 2 && subid == subid_written);
+}
+
+/*
+ * LookupGXactBySubid
+ *		Check if the prepared transaction done by apply worker exists.
+ */
+bool
+LookupGXactBySubid(Oid subid)
+{
+	bool		found = false;
+
+	LWLockAcquire(TwoPhaseStateLock, LW_SHARED);
+	for (int i = 0; i < TwoPhaseState->numPrepXacts; i++)
+	{
+		GlobalTransaction gxact = TwoPhaseState->prepXacts[i];
+
+		/* Ignore not-yet-valid GIDs. */
+		if (gxact->valid &&
+			IsTwoPhaseTransactionGidForSubid(subid, gxact->gid))
+		{
+			found = true;
+			break;
+		}
+	}
+	LWLockRelease(TwoPhaseStateLock);
+	return found;
+}
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index e407428dbc..1a2f0c1e64 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -16,6 +16,7 @@
 
 #include "access/htup_details.h"
 #include "access/table.h"
+#include "access/twophase.h"
 #include "access/xact.h"
 #include "catalog/catalog.h"
 #include "catalog/dependency.h"
@@ -1143,7 +1144,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 			{
 				supported_opts = (SUBOPT_SLOT_NAME |
 								  SUBOPT_SYNCHRONOUS_COMMIT | SUBOPT_BINARY |
-								  SUBOPT_STREAMING | SUBOPT_DISABLE_ON_ERR |
+								  SUBOPT_STREAMING | SUBOPT_TWOPHASE_COMMIT |
+								  SUBOPT_DISABLE_ON_ERR |
 								  SUBOPT_PASSWORD_REQUIRED |
 								  SUBOPT_RUN_AS_OWNER | SUBOPT_FAILOVER |
 								  SUBOPT_ORIGIN);
@@ -1151,6 +1153,53 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 				parse_subscription_options(pstate, stmt->options,
 										   supported_opts, &opts);
 
+				if (IsSet(opts.specified_opts, SUBOPT_TWOPHASE_COMMIT))
+				{
+					/*
+					 * Do not allow changing the two_phase option if the
+					 * subscription is enabled. This is because the two_phase
+					 * option of the slot on the publisher cannot be modified
+					 * if the slot is currently acquired by the apply worker.
+					 */
+					if (form->subenabled)
+						ereport(ERROR,
+								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+								 errmsg("cannot set %s for enabled subscription",
+										"two_phase")));
+
+					/*
+					 * Stop all the subscription workers, just in case. Workers
+					 * may still survive even if the subscription is disabled.
+					 */
+					logicalrep_workers_stop(subid);
+
+					/*
+					 * two_phase cannot be disabled if there are any
+					 * uncommitted prepared transactions present.
+					 */
+					if (!opts.twophase &&
+						form->subtwophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
+						LookupGXactBySubid(subid))
+						/* Add error message */
+						ereport(ERROR,
+								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+								 errmsg("cannot disable two_phase when uncommitted prepared transactions present"),
+								 errhint("Resolve these transactions and try again")));
+
+					/*
+					 * The changed two_phase option of the slot can't be rolled
+					 * back.
+					 */
+					PreventInTransactionBlock(isTopLevel, "ALTER SUBSCRIPTION ... SET (two_phase)");
+
+					/* Change system catalog acoordingly */
+					values[Anum_pg_subscription_subtwophasestate - 1] =
+						CharGetDatum(opts.twophase ?
+									 LOGICALREP_TWOPHASE_STATE_PENDING :
+									 LOGICALREP_TWOPHASE_STATE_DISABLED);
+					replaces[Anum_pg_subscription_subtwophasestate - 1] = true;
+				}
+
 				if (IsSet(opts.specified_opts, SUBOPT_SLOT_NAME))
 				{
 					/*
@@ -1505,7 +1554,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 	 * doing the database operations we won't be able to rollback altered
 	 * slot.
 	 */
-	if (replaces[Anum_pg_subscription_subfailover - 1])
+	if (replaces[Anum_pg_subscription_subfailover - 1] ||
+		replaces[Anum_pg_subscription_subtwophasestate - 1])
 	{
 		bool		must_use_password;
 		char	   *err;
@@ -1525,7 +1575,7 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 
 		PG_TRY();
 		{
-			walrcv_alter_slot(wrconn, sub->slotname, opts.failover);
+			walrcv_alter_slot(wrconn, sub->slotname, opts.failover, opts.twophase);
 		}
 		PG_FINALLY();
 		{
@@ -1562,7 +1612,6 @@ DropSubscription(DropSubscriptionStmt *stmt, bool isTopLevel)
 	char	   *subname;
 	char	   *conninfo;
 	char	   *slotname;
-	List	   *subworkers;
 	ListCell   *lc;
 	char		originname[NAMEDATALEN];
 	char	   *err = NULL;
@@ -1672,16 +1721,7 @@ DropSubscription(DropSubscriptionStmt *stmt, bool isTopLevel)
 	 * New workers won't be started because we hold an exclusive lock on the
 	 * subscription till the end of the transaction.
 	 */
-	LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
-	subworkers = logicalrep_workers_find(subid, false);
-	LWLockRelease(LogicalRepWorkerLock);
-	foreach(lc, subworkers)
-	{
-		LogicalRepWorker *w = (LogicalRepWorker *) lfirst(lc);
-
-		logicalrep_worker_stop(w->subid, w->relid);
-	}
-	list_free(subworkers);
+	logicalrep_workers_stop(subid);
 
 	/*
 	 * Remove the no-longer-useful entry in the launcher's table of apply
diff --git a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
index 3c2b1bb496..998bbd517a 100644
--- a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
+++ b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
@@ -80,7 +80,7 @@ static char *libpqrcv_create_slot(WalReceiverConn *conn,
 								  CRSSnapshotAction snapshot_action,
 								  XLogRecPtr *lsn);
 static void libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-								bool failover);
+								bool failover, bool two_phase);
 static pid_t libpqrcv_get_backend_pid(WalReceiverConn *conn);
 static WalRcvExecResult *libpqrcv_exec(WalReceiverConn *conn,
 									   const char *query,
@@ -1121,15 +1121,16 @@ libpqrcv_create_slot(WalReceiverConn *conn, const char *slotname,
  */
 static void
 libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-					bool failover)
+					bool failover, bool two_phase)
 {
 	StringInfoData cmd;
 	PGresult   *res;
 
 	initStringInfo(&cmd);
-	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( FAILOVER %s )",
+	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( FAILOVER %s, TWO_PHASE %s )",
 					 quote_identifier(slotname),
-					 failover ? "true" : "false");
+					 failover ? "true" : "false",
+					 two_phase ? "true" : "false");
 
 	res = libpqrcv_PQexec(conn->streamConn, cmd.data);
 	pfree(cmd.data);
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 66070e9131..548f6e0edb 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -623,6 +623,28 @@ logicalrep_worker_stop(Oid subid, Oid relid)
 	LWLockRelease(LogicalRepWorkerLock);
 }
 
+/*
+ * Stop all the subscription workers.
+ */
+void
+logicalrep_workers_stop(Oid subid)
+{
+	List	   *subworkers;
+	ListCell   *lc;
+
+	LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
+	/* XXX clarify the reason why not only running workers are listed. */
+	subworkers = logicalrep_workers_find(subid, false);
+	LWLockRelease(LogicalRepWorkerLock);
+	foreach(lc, subworkers)
+	{
+		LogicalRepWorker *w = (LogicalRepWorker *) lfirst(lc);
+
+		logicalrep_worker_stop(w->subid, w->relid);
+	}
+	list_free(subworkers);
+}
+
 /*
  * Stop the given logical replication parallel apply worker.
  *
diff --git a/src/backend/replication/logical/worker.c b/src/backend/replication/logical/worker.c
index b5a80fe3e8..dcf656fd45 100644
--- a/src/backend/replication/logical/worker.c
+++ b/src/backend/replication/logical/worker.c
@@ -402,7 +402,6 @@ static void apply_handle_tuple_routing(ApplyExecutionData *edata,
 									   CmdType operation);
 
 /* Compute GID for two_phase transactions */
-static void TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid, int szgid);
 
 /* Functions for skipping changes */
 static void maybe_start_skipping_changes(XLogRecPtr finish_lsn);
@@ -3911,7 +3910,7 @@ maybe_reread_subscription(void)
 	/* !slotname should never happen when enabled is true. */
 	Assert(newsub->slotname);
 
-	/* two-phase should not be altered */
+	/* two-phase cannot be altered while the worker exists */
 	Assert(newsub->twophasestate == MySubscription->twophasestate);
 
 	/*
@@ -4396,24 +4395,6 @@ cleanup_subxact_info()
 	subxact_data.nsubxacts_max = 0;
 }
 
-/*
- * Form the prepared transaction GID for two_phase transactions.
- *
- * Return the GID in the supplied buffer.
- */
-static void
-TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid, int szgid)
-{
-	Assert(subid != InvalidRepOriginId);
-
-	if (!TransactionIdIsValid(xid))
-		ereport(ERROR,
-				(errcode(ERRCODE_PROTOCOL_VIOLATION),
-				 errmsg_internal("invalid two-phase transaction ID")));
-
-	snprintf(gid, szgid, "pg_gid_%u_%u", subid, xid);
-}
-
 /*
  * Common function to run the apply loop with error handling. Disable the
  * subscription, if necessary.
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index aa4ea387da..d0c8d5a4df 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -804,8 +804,10 @@ ReplicationSlotDrop(const char *name, bool nowait)
  * Change the definition of the slot identified by the specified name.
  */
 void
-ReplicationSlotAlter(const char *name, bool failover)
+ReplicationSlotAlter(const char *name, bool failover, bool two_phase)
 {
+	bool		update_slot = false;
+
 	Assert(MyReplicationSlot == NULL);
 
 	ReplicationSlotAcquire(name, false);
@@ -854,6 +856,20 @@ ReplicationSlotAlter(const char *name, bool failover)
 		MyReplicationSlot->data.failover = failover;
 		SpinLockRelease(&MyReplicationSlot->mutex);
 
+		update_slot = true;
+	}
+
+	if (MyReplicationSlot->data.two_phase != two_phase)
+	{
+		SpinLockAcquire(&MyReplicationSlot->mutex);
+		MyReplicationSlot->data.two_phase = two_phase;
+		SpinLockRelease(&MyReplicationSlot->mutex);
+
+		update_slot = true;
+	}
+
+	if (update_slot)
+	{
 		ReplicationSlotMarkDirty();
 		ReplicationSlotSave();
 	}
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index c623b07cf0..2e6ca35049 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1411,9 +1411,11 @@ DropReplicationSlot(DropReplicationSlotCmd *cmd)
  * Process extra options given to ALTER_REPLICATION_SLOT.
  */
 static void
-ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd, bool *failover)
+ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd,
+						  bool *failover, bool *two_phase)
 {
 	bool		failover_given = false;
+	bool		two_phase_given = false;
 
 	/* Parse options */
 	foreach_ptr(DefElem, defel, cmd->options)
@@ -1427,6 +1429,15 @@ ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd, bool *failover)
 			failover_given = true;
 			*failover = defGetBoolean(defel);
 		}
+		else if (strcmp(defel->defname, "two_phase") == 0)
+		{
+			if (two_phase_given)
+				ereport(ERROR,
+						(errcode(ERRCODE_SYNTAX_ERROR),
+						 errmsg("conflicting or redundant options")));
+			two_phase_given = true;
+			*two_phase = defGetBoolean(defel);
+		}
 		else
 			elog(ERROR, "unrecognized option: %s", defel->defname);
 	}
@@ -1439,9 +1450,10 @@ static void
 AlterReplicationSlot(AlterReplicationSlotCmd *cmd)
 {
 	bool		failover = false;
+	bool		two_phase = false;
 
-	ParseAlterReplSlotOptions(cmd, &failover);
-	ReplicationSlotAlter(cmd->slotname, failover);
+	ParseAlterReplSlotOptions(cmd, &failover, &two_phase);
+	ReplicationSlotAlter(cmd->slotname, failover, two_phase);
 }
 
 /*
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
index d453e224d9..891face1b6 100644
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -1948,7 +1948,7 @@ psql_completion(const char *text, int start, int end)
 	else if (HeadMatches("ALTER", "SUBSCRIPTION", MatchAny) && TailMatches("SET", "("))
 		COMPLETE_WITH("binary", "disable_on_error", "failover", "origin",
 					  "password_required", "run_as_owner", "slot_name",
-					  "streaming", "synchronous_commit");
+					  "streaming", "synchronous_commit", "two_phase");
 	/* ALTER SUBSCRIPTION <name> SKIP ( */
 	else if (HeadMatches("ALTER", "SUBSCRIPTION", MatchAny) && TailMatches("SKIP", "("))
 		COMPLETE_WITH("lsn");
diff --git a/src/include/access/twophase.h b/src/include/access/twophase.h
index 56248c0006..d37e06fdee 100644
--- a/src/include/access/twophase.h
+++ b/src/include/access/twophase.h
@@ -62,4 +62,9 @@ extern void PrepareRedoRemove(TransactionId xid, bool giveWarning);
 extern void restoreTwoPhaseData(void);
 extern bool LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 						TimestampTz origin_prepare_timestamp);
+
+extern void TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid,
+								   int szgid);
+extern bool LookupGXactBySubid(Oid subid);
+
 #endif							/* TWOPHASE_H */
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 1bc80960ef..014e216cf5 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -243,7 +243,8 @@ extern void ReplicationSlotCreate(const char *name, bool db_specific,
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
 extern void ReplicationSlotDropAcquired(void);
-extern void ReplicationSlotAlter(const char *name, bool failover);
+extern void ReplicationSlotAlter(const char *name, bool failover,
+								 bool two_phase);
 
 extern void ReplicationSlotAcquire(const char *name, bool nowait);
 extern void ReplicationSlotRelease(void);
diff --git a/src/include/replication/walreceiver.h b/src/include/replication/walreceiver.h
index 12f71fa99b..31fa1257ec 100644
--- a/src/include/replication/walreceiver.h
+++ b/src/include/replication/walreceiver.h
@@ -372,12 +372,13 @@ typedef char *(*walrcv_create_slot_fn) (WalReceiverConn *conn,
 /*
  * walrcv_alter_slot_fn
  *
- * Change the definition of a replication slot. Currently, it only supports
- * changing the failover property of the slot.
+ * Change the definition of a replication slot. Currently, it supports
+ * changing the failover and the two_phase property of the slot.
  */
 typedef void (*walrcv_alter_slot_fn) (WalReceiverConn *conn,
 									  const char *slotname,
-									  bool failover);
+									  bool failover,
+									  bool two_phase);
 
 /*
  * walrcv_get_backend_pid_fn
@@ -455,8 +456,8 @@ extern PGDLLIMPORT WalReceiverFunctionsType *WalReceiverFunctions;
 	WalReceiverFunctions->walrcv_send(conn, buffer, nbytes)
 #define walrcv_create_slot(conn, slotname, temporary, two_phase, failover, snapshot_action, lsn) \
 	WalReceiverFunctions->walrcv_create_slot(conn, slotname, temporary, two_phase, failover, snapshot_action, lsn)
-#define walrcv_alter_slot(conn, slotname, failover) \
-	WalReceiverFunctions->walrcv_alter_slot(conn, slotname, failover)
+#define walrcv_alter_slot(conn, slotname, failover, two_phase) \
+	WalReceiverFunctions->walrcv_alter_slot(conn, slotname, failover, two_phase)
 #define walrcv_get_backend_pid(conn) \
 	WalReceiverFunctions->walrcv_get_backend_pid(conn)
 #define walrcv_exec(conn, exec, nRetTypes, retTypes) \
diff --git a/src/include/replication/worker_internal.h b/src/include/replication/worker_internal.h
index 515aefd519..d5428263c1 100644
--- a/src/include/replication/worker_internal.h
+++ b/src/include/replication/worker_internal.h
@@ -246,6 +246,7 @@ extern bool logicalrep_worker_launch(LogicalRepWorkerType wtype,
 									 Oid userid, Oid relid,
 									 dsm_handle subworker_dsm);
 extern void logicalrep_worker_stop(Oid subid, Oid relid);
+extern void logicalrep_workers_stop(Oid subid);
 extern void logicalrep_pa_worker_stop(ParallelApplyWorkerInfo *winfo);
 extern void logicalrep_worker_wakeup(Oid subid, Oid relid);
 extern void logicalrep_worker_wakeup_ptr(LogicalRepWorker *worker);
diff --git a/src/test/regress/expected/subscription.out b/src/test/regress/expected/subscription.out
index 0f2a25cdc1..51fa4b9690 100644
--- a/src/test/regress/expected/subscription.out
+++ b/src/test/regress/expected/subscription.out
@@ -377,10 +377,7 @@ HINT:  To initiate replication, you must manually create the replication slot, e
  regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | p                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
---fail - alter of two_phase option not supported.
-ALTER SUBSCRIPTION regress_testsub SET (two_phase = false);
-ERROR:  unrecognized subscription parameter: "two_phase"
--- but can alter streaming when two_phase enabled
+-- We can alter streaming when two_phase enabled
 ALTER SUBSCRIPTION regress_testsub SET (streaming = true);
 \dRs+
                                                                                                                 List of subscriptions
diff --git a/src/test/regress/sql/subscription.sql b/src/test/regress/sql/subscription.sql
index 3e5ba4cb8c..a3886d79ca 100644
--- a/src/test/regress/sql/subscription.sql
+++ b/src/test/regress/sql/subscription.sql
@@ -256,10 +256,7 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUBLICATION testpub WITH (connect = false, two_phase = true);
 
 \dRs+
---fail - alter of two_phase option not supported.
-ALTER SUBSCRIPTION regress_testsub SET (two_phase = false);
-
--- but can alter streaming when two_phase enabled
+-- We can alter streaming when two_phase enabled
 ALTER SUBSCRIPTION regress_testsub SET (streaming = true);
 
 \dRs+
diff --git a/src/test/subscription/t/021_twophase.pl b/src/test/subscription/t/021_twophase.pl
index 9437cd4c3b..72df258000 100644
--- a/src/test/subscription/t/021_twophase.pl
+++ b/src/test/subscription/t/021_twophase.pl
@@ -367,6 +367,75 @@ $result =
   $node_subscriber->safe_psql('postgres', "SELECT count(*) FROM tab_copy;");
 is($result, qq(2), 'replicated data in subscriber table');
 
+# Clean up
+$node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub");
+
+###############################
+# Disable the subscription and alter it to two_phase = false,
+# then verify that the altered subscription reflects the two_phase option.
+###############################
+
+# Alter subscription two_phase to false
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy DISABLE");
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = false)");
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy ENABLE");
+
+# Wait for subscription startup
+$node_subscriber->wait_for_subscription_sync($node_publisher, $appname_copy);
+
+# Make sure that the two-phase is disabled on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+       "SELECT subtwophasestate FROM pg_subscription WHERE subname = 'tap_sub_copy';"
+);
+is($result, qq(d), 'two-phase should be disabled');
+
+# Now do a prepare on the publisher and make sure that it is not replicated.
+$node_publisher->safe_psql(
+       'postgres', qq{
+    BEGIN;
+    INSERT INTO tab_copy VALUES (100);
+    PREPARE TRANSACTION 'newgid';
+	});
+
+# Wait for the subscriber to catchup
+$node_publisher->wait_for_catchup($appname_copy);
+
+# Make sure there are no prepared transactions on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT count(*) FROM pg_prepared_xacts;");
+is($result, qq(0), 'should be no prepared transactions on subscriber');
+
+# Now commit the insert and verify that it IS replicated
+$node_publisher->safe_psql('postgres', "COMMIT PREPARED 'newgid';");
+
+# Wait for the subscriber to catchup
+$node_publisher->wait_for_catchup($appname_copy);
+
+# Make sure that the committed transaction is replicated.
+$result =
+	$node_subscriber->safe_psql('postgres', "SELECT count(*) FROM tab_copy;");
+is($result, qq(3), 'replicated data in subscriber table');
+
+# Alter subscription two_phase to true
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy DISABLE");
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = true)");
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy ENABLE");
+
+# Wait for subscription startup
+$node_subscriber->wait_for_subscription_sync($node_publisher, $appname_copy);
+
+# Make sure that the two-phase is enabled on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT subtwophasestate FROM pg_subscription WHERE subname = 'tap_sub_copy';"
+);
+is($result, qq(e), 'two-phase should be enabled');
+
 $node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub_copy;");
 $node_publisher->safe_psql('postgres', "DROP PUBLICATION tap_pub_copy;");
 
@@ -374,8 +443,6 @@ $node_publisher->safe_psql('postgres', "DROP PUBLICATION tap_pub_copy;");
 # check all the cleanup
 ###############################
 
-$node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub");
-
 $result = $node_subscriber->safe_psql('postgres',
 	"SELECT count(*) FROM pg_subscription");
 is($result, qq(0), 'check subscription was dropped on subscriber');
-- 
2.43.0

From 1f65aaeacb63502cf6f2eb0d6f3889037a1bff9f Mon Sep 17 00:00:00 2001
From: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Date: Wed, 17 Apr 2024 06:18:23 +0000
Subject: [PATCH v7 2/4] Alter slot option two_phase only when altering true to
 false

---
 doc/src/sgml/ref/alter_subscription.sgml      |  2 +-
 src/backend/commands/subscriptioncmds.c       | 23 +++++-
 .../libpqwalreceiver/libpqwalreceiver.c       | 21 ++++--
 src/include/replication/walreceiver.h         |  5 +-
 src/test/subscription/meson.build             |  1 +
 src/test/subscription/t/099_twophase_added.pl | 72 +++++++++++++++++++
 6 files changed, 113 insertions(+), 11 deletions(-)
 create mode 100644 src/test/subscription/t/099_twophase_added.pl

diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index 88e9a72147..0c2894a94e 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -70,7 +70,7 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
    <command>ALTER SUBSCRIPTION ... {SET|ADD|DROP} PUBLICATION ...</command>
    with <literal>refresh</literal> option as <literal>true</literal>,
    <command>ALTER SUBSCRIPTION ... SET (failover = on|off)</command> and
-   <command>ALTER SUBSCRIPTION ... SET (two_phase = on|off)</command>
+   <command>ALTER SUBSCRIPTION ... SET (two_phase = off)</command>
    cannot be executed inside a transaction block.
 
    These commands also cannot be executed when the subscription has
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index 1a2f0c1e64..71b058b385 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -1190,7 +1190,9 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 					 * The changed two_phase option of the slot can't be rolled
 					 * back.
 					 */
-					PreventInTransactionBlock(isTopLevel, "ALTER SUBSCRIPTION ... SET (two_phase)");
+					if (!opts.twophase)
+						PreventInTransactionBlock(isTopLevel,
+												  "ALTER SUBSCRIPTION ... SET (two_phase = off)");
 
 					/* Change system catalog acoordingly */
 					values[Anum_pg_subscription_subtwophasestate - 1] =
@@ -1560,6 +1562,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 		bool		must_use_password;
 		char	   *err;
 		WalReceiverConn *wrconn;
+		bool		failover_needs_to_be_updated;
+		bool		two_phase_needs_to_be_updated;
 
 		/* Load the library providing us libpq calls. */
 		load_file("libpqwalreceiver", false);
@@ -1573,9 +1577,24 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 					(errcode(ERRCODE_CONNECTION_FAILURE),
 					 errmsg("could not connect to the publisher: %s", err)));
 
+		/*
+		 * Consider which slot option must be altered.
+		 *
+		 * We must alter the failover option whenever subfailover is updated.
+		 * Two_phase, however, is altered only when changing true to false.
+		 */
+		failover_needs_to_be_updated =
+								replaces[Anum_pg_subscription_subfailover - 1];
+		two_phase_needs_to_be_updated =
+						(replaces[Anum_pg_subscription_subtwophasestate - 1] &&
+						 !opts.twophase);
+
 		PG_TRY();
 		{
-			walrcv_alter_slot(wrconn, sub->slotname, opts.failover, opts.twophase);
+			if (two_phase_needs_to_be_updated || failover_needs_to_be_updated)
+				walrcv_alter_slot(wrconn, sub->slotname,
+								  failover_needs_to_be_updated ? &opts.failover : NULL,
+								  two_phase_needs_to_be_updated ? &opts.twophase : NULL);
 		}
 		PG_FINALLY();
 		{
diff --git a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
index 998bbd517a..c383767096 100644
--- a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
+++ b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
@@ -80,7 +80,7 @@ static char *libpqrcv_create_slot(WalReceiverConn *conn,
 								  CRSSnapshotAction snapshot_action,
 								  XLogRecPtr *lsn);
 static void libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-								bool failover, bool two_phase);
+								const bool *failover, const bool *two_phase);
 static pid_t libpqrcv_get_backend_pid(WalReceiverConn *conn);
 static WalRcvExecResult *libpqrcv_exec(WalReceiverConn *conn,
 									   const char *query,
@@ -1121,16 +1121,25 @@ libpqrcv_create_slot(WalReceiverConn *conn, const char *slotname,
  */
 static void
 libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-					bool failover, bool two_phase)
+					const bool *failover, const bool *two_phase)
 {
 	StringInfoData cmd;
 	PGresult   *res;
 
 	initStringInfo(&cmd);
-	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( FAILOVER %s, TWO_PHASE %s )",
-					 quote_identifier(slotname),
-					 failover ? "true" : "false",
-					 two_phase ? "true" : "false");
+	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( ",
+					 quote_identifier(slotname));
+
+	if (failover)
+		appendStringInfo(&cmd, "FAILOVER %s ",
+						 (*failover) ? "true" : "false");
+
+	if (two_phase)
+		appendStringInfo(&cmd, "TWO_PHASE %s%s ",
+						 (*two_phase) ? "true" : "false",
+						 failover ? ", " : "");
+
+	appendStringInfoString(&cmd, ");");
 
 	res = libpqrcv_PQexec(conn->streamConn, cmd.data);
 	pfree(cmd.data);
diff --git a/src/include/replication/walreceiver.h b/src/include/replication/walreceiver.h
index 31fa1257ec..7ffa5a58b3 100644
--- a/src/include/replication/walreceiver.h
+++ b/src/include/replication/walreceiver.h
@@ -377,8 +377,9 @@ typedef char *(*walrcv_create_slot_fn) (WalReceiverConn *conn,
  */
 typedef void (*walrcv_alter_slot_fn) (WalReceiverConn *conn,
 									  const char *slotname,
-									  bool failover,
-									  bool two_phase);
+									  const bool *failover,
+									  const bool *two_phase);
+
 
 /*
  * walrcv_get_backend_pid_fn
diff --git a/src/test/subscription/meson.build b/src/test/subscription/meson.build
index c591cd7d61..b4bd522c3d 100644
--- a/src/test/subscription/meson.build
+++ b/src/test/subscription/meson.build
@@ -40,6 +40,7 @@ tests += {
       't/031_column_list.pl',
       't/032_subscribe_use_index.pl',
       't/033_run_as_table_owner.pl',
+      't/099_twophase_added.pl',
       't/100_bugs.pl',
     ],
   },
diff --git a/src/test/subscription/t/099_twophase_added.pl b/src/test/subscription/t/099_twophase_added.pl
new file mode 100644
index 0000000000..c13a37675a
--- /dev/null
+++ b/src/test/subscription/t/099_twophase_added.pl
@@ -0,0 +1,72 @@
+# Copyright (c) 2021-2024, PostgreSQL Global Development Group
+
+# Additional tests for altering two_phase option
+use strict;
+use warnings FATAL => 'all';
+use PostgreSQL::Test::Cluster;
+use PostgreSQL::Test::Utils;
+use Test::More;
+
+# Initialize publisher node
+my $node_publisher = PostgreSQL::Test::Cluster->new('publisher');
+$node_publisher->init(allows_streaming => 'logical');
+$node_publisher->append_conf('postgresql.conf',
+	qq(max_prepared_transactions = 10));
+$node_publisher->start;
+
+# Create subscriber node
+my $node_subscriber = PostgreSQL::Test::Cluster->new('subscriber');
+$node_subscriber->init;
+$node_subscriber->append_conf('postgresql.conf',
+	qq(max_prepared_transactions = 10));
+$node_subscriber->start;
+
+# Define pre-existing tables on both nodes
+$node_publisher->safe_psql('postgres',
+    "CREATE TABLE tab_full (a int PRIMARY KEY);");
+$node_subscriber->safe_psql('postgres',
+	"CREATE TABLE tab_full (a int PRIMARY KEY)");
+
+# Setup logical replication, with two_phase = off
+my $publisher_connstr = $node_publisher->connstr . ' dbname=postgres';
+$node_publisher->safe_psql('postgres',
+	"CREATE PUBLICATION pub FOR ALL TABLES");
+
+$node_subscriber->safe_psql(
+	'postgres', "
+	CREATE SUBSCRIPTION sub
+	CONNECTION '$publisher_connstr' PUBLICATION pub
+	WITH (two_phase = off, copy_data = off)");
+
+######
+# Check the case that prepared transactions exist on publisher node
+######
+
+$node_publisher->safe_psql(
+	'postgres', "
+	BEGIN;
+	INSERT INTO tab_full VALUES (generate_series(1, 5));
+	PREPARE TRANSACTION 'test_prepared_tab_full';");
+
+$node_publisher->wait_for_catchup('sub');
+
+my $result = $node_subscriber->safe_psql('postgres',
+    "SELECT count(*) FROM pg_prepared_xacts;");
+is($result, q(0), "transaction is not prepared on subscriber");
+
+$node_subscriber->safe_psql(
+    'postgres', "
+    ALTER SUBSCRIPTION sub DISABLE;
+    ALTER SUBSCRIPTION sub SET (two_phase = on);
+    ALTER SUBSCRIPTION sub ENABLE;");
+
+$node_publisher->safe_psql( 'postgres',
+    "COMMIT PREPARED 'test_prepared_tab_full';");
+$node_publisher->wait_for_catchup('sub');
+
+$result = $node_subscriber->safe_psql('postgres',
+    "SELECT count(*) FROM tab_full;");
+is($result, q(5),
+   "prepared transactions done before altering can be replicated");
+
+done_testing();
-- 
2.43.0

From c23330158b9e7407922d766d4c7ea6113eda14b2 Mon Sep 17 00:00:00 2001
From: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Date: Mon, 8 Apr 2024 12:39:12 +0000
Subject: [PATCH v7 3/4] Abort prepared transactions while altering two_phase
 to false

---
 doc/src/sgml/ref/alter_subscription.sgml      |  9 ++++-
 src/backend/access/transam/twophase.c         | 17 ++++----
 src/backend/commands/subscriptioncmds.c       | 39 ++++++++++++-------
 src/include/access/twophase.h                 |  3 +-
 src/test/subscription/t/099_twophase_added.pl | 35 +++++++++++++++++
 5 files changed, 75 insertions(+), 28 deletions(-)

diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index 0c2894a94e..848e4af649 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -233,8 +233,6 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>, and
       <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>.
       Only a superuser can set <literal>password_required = false</literal>.
-      The <literal>two_phase</literal> parameter can only be altered when the
-      subscription is disabled.
      </para>
 
      <para>
@@ -256,6 +254,13 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>
       option is enabled.
      </para>
+
+     <para>
+      The <literal>two_phase</literal> parameter can only be altered when the
+      subscription is disabled. When altering the parameter from <literal>true</literal>
+      to <literal>false</literal>, the backend process checks prepared
+      transactions done by the logical replication worker and aborts them.
+     </para>
     </listitem>
    </varlistentry>
 
diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index a67a8c48aa..e0cc0e9b21 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -2719,13 +2719,13 @@ IsTwoPhaseTransactionGidForSubid(Oid subid, char *gid)
 }
 
 /*
- * LookupGXactBySubid
- *		Check if the prepared transaction done by apply worker exists.
+ * GetGidListBySubid
+ *      Get a list of GIDs which is PREPARE'd by the given subscription.
  */
-bool
-LookupGXactBySubid(Oid subid)
+List *
+GetGidListBySubid(Oid subid)
 {
-	bool		found = false;
+	List *list = NIL;
 
 	LWLockAcquire(TwoPhaseStateLock, LW_SHARED);
 	for (int i = 0; i < TwoPhaseState->numPrepXacts; i++)
@@ -2735,11 +2735,8 @@ LookupGXactBySubid(Oid subid)
 		/* Ignore not-yet-valid GIDs. */
 		if (gxact->valid &&
 			IsTwoPhaseTransactionGidForSubid(subid, gxact->gid))
-		{
-			found = true;
-			break;
-		}
+			list = lappend(list, pstrdup(gxact->gid));
 	}
 	LWLockRelease(TwoPhaseStateLock);
-	return found;
+	return list;
 }
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index 71b058b385..27be6299e0 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -1155,6 +1155,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 
 				if (IsSet(opts.specified_opts, SUBOPT_TWOPHASE_COMMIT))
 				{
+					List *prepared_xacts = NIL;
+
 					/*
 					 * Do not allow changing the two_phase option if the
 					 * subscription is enabled. This is because the two_phase
@@ -1174,26 +1176,33 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 					logicalrep_workers_stop(subid);
 
 					/*
-					 * two_phase cannot be disabled if there are any
-					 * uncommitted prepared transactions present.
-					 */
-					if (!opts.twophase &&
-						form->subtwophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
-						LookupGXactBySubid(subid))
-						/* Add error message */
-						ereport(ERROR,
-								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-								 errmsg("cannot disable two_phase when uncommitted prepared transactions present"),
-								 errhint("Resolve these transactions and try again")));
-
-					/*
-					 * The changed two_phase option of the slot can't be rolled
-					 * back.
+					 * If two_phase was enabled, there is a possibility the
+					 * transactions has already been PREPARE'd. They must be
+					 * checked and rolled back.
 					 */
 					if (!opts.twophase)
+					{
+						/*
+						 * The changed two_phase option (true->false) of the
+						 * slot can't be rolled back.
+						 */
 						PreventInTransactionBlock(isTopLevel,
 												  "ALTER SUBSCRIPTION ... SET (two_phase = off)");
 
+						if (sub->twophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
+							(prepared_xacts = GetGidListBySubid(subid)) != NIL)
+						{
+							ListCell	*cell;
+
+							/* Abort all listed transactions */
+							foreach(cell, prepared_xacts)
+								FinishPreparedTransaction((char *) lfirst(cell),
+														  false);
+
+							list_free(prepared_xacts);
+						}
+					}
+
 					/* Change system catalog acoordingly */
 					values[Anum_pg_subscription_subtwophasestate - 1] =
 						CharGetDatum(opts.twophase ?
diff --git a/src/include/access/twophase.h b/src/include/access/twophase.h
index d37e06fdee..f7a5cf0c12 100644
--- a/src/include/access/twophase.h
+++ b/src/include/access/twophase.h
@@ -18,6 +18,7 @@
 #include "access/xlogdefs.h"
 #include "datatype/timestamp.h"
 #include "storage/lock.h"
+#include "nodes/pg_list.h"
 
 /*
  * GlobalTransactionData is defined in twophase.c; other places have no
@@ -65,6 +66,6 @@ extern bool LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 
 extern void TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid,
 								   int szgid);
-extern bool LookupGXactBySubid(Oid subid);
+extern List *GetGidListBySubid(Oid subid);
 
 #endif							/* TWOPHASE_H */
diff --git a/src/test/subscription/t/099_twophase_added.pl b/src/test/subscription/t/099_twophase_added.pl
index c13a37675a..a8135b671c 100644
--- a/src/test/subscription/t/099_twophase_added.pl
+++ b/src/test/subscription/t/099_twophase_added.pl
@@ -69,4 +69,39 @@ $result = $node_subscriber->safe_psql('postgres',
 is($result, q(5),
    "prepared transactions done before altering can be replicated");
 
+######
+# Check the case that prepared transactions exist on subscriber node
+######
+
+$node_publisher->safe_psql(
+	'postgres', "
+	BEGIN;
+	INSERT INTO tab_full VALUES (generate_series(6, 10));
+	PREPARE TRANSACTION 'test_prepared_tab_full';");
+
+$node_publisher->wait_for_catchup('sub');
+
+$result = $node_subscriber->safe_psql('postgres',
+    "SELECT count(*) FROM pg_prepared_xacts;");
+is($result, q(1), "transaction has been prepared on subscriber");
+
+$node_subscriber->safe_psql(
+    'postgres', "
+    ALTER SUBSCRIPTION sub DISABLE;
+    ALTER SUBSCRIPTION sub SET (two_phase = off);
+    ALTER SUBSCRIPTION sub ENABLE;");
+
+$result = $node_subscriber->safe_psql('postgres',
+    "SELECT count(*) FROM pg_prepared_xacts;");
+is($result, q(0), "prepared transaction done by worker is aborted");
+
+$node_publisher->safe_psql( 'postgres',
+    "COMMIT PREPARED 'test_prepared_tab_full';");
+$node_publisher->wait_for_catchup('sub');
+
+$result = $node_subscriber->safe_psql('postgres',
+    "SELECT count(10) FROM tab_full;");
+is($result, q(10),
+   "prepared transactions on publisher can be replicated");
+
 done_testing();
-- 
2.43.0

From 71feafb120da3a499f15427d5e9c4f41800cf6c6 Mon Sep 17 00:00:00 2001
From: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Date: Fri, 19 Apr 2024 11:03:19 +0000
Subject: [PATCH v7 4/4] Add force_alter option

---
 doc/src/sgml/ref/alter_subscription.sgml      |  9 +++--
 src/backend/commands/subscriptioncmds.c       | 33 ++++++++++++++++++-
 src/test/regress/expected/subscription.out    |  3 ++
 src/test/regress/sql/subscription.sql         |  3 ++
 src/test/subscription/t/099_twophase_added.pl | 23 ++++++++++---
 5 files changed, 62 insertions(+), 9 deletions(-)

diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index 848e4af649..bbfaa72229 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -257,9 +257,12 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
 
      <para>
       The <literal>two_phase</literal> parameter can only be altered when the
-      subscription is disabled. When altering the parameter from <literal>true</literal>
-      to <literal>false</literal>, the backend process checks prepared
-      transactions done by the logical replication worker and aborts them.
+      subscription is disabled. Altering the parameter from <literal>true</literal>
+      to <literal>false</literal> will be failed when there are prepared
+      transactions done by the logical replication worker. If you want to alter
+      the parameter forcibly in this case, <literal>force_alter</literal>
+      option must be set to <literal>true</literal> at the same time. If
+      specified, the backend process aborts prepared transactions.
      </para>
     </listitem>
    </varlistentry>
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index 27be6299e0..512357f9a4 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -73,6 +73,7 @@
 #define SUBOPT_FAILOVER				0x00002000
 #define SUBOPT_LSN					0x00004000
 #define SUBOPT_ORIGIN				0x00008000
+#define SUBOPT_FORCE_ALTER			0x00010000
 
 /* check if the 'val' has 'bits' set */
 #define IsSet(val, bits)  (((val) & (bits)) == (bits))
@@ -100,6 +101,7 @@ typedef struct SubOpts
 	bool		failover;
 	char	   *origin;
 	XLogRecPtr	lsn;
+	bool		twophase_force;
 } SubOpts;
 
 static List *fetch_table_list(WalReceiverConn *wrconn, List *publications);
@@ -162,6 +164,8 @@ parse_subscription_options(ParseState *pstate, List *stmt_options,
 		opts->failover = false;
 	if (IsSet(supported_opts, SUBOPT_ORIGIN))
 		opts->origin = pstrdup(LOGICALREP_ORIGIN_ANY);
+	if (IsSet(supported_opts, SUBOPT_FORCE_ALTER))
+		opts->twophase_force = false;
 
 	/* Parse options */
 	foreach(lc, stmt_options)
@@ -367,6 +371,15 @@ parse_subscription_options(ParseState *pstate, List *stmt_options,
 			opts->specified_opts |= SUBOPT_LSN;
 			opts->lsn = lsn;
 		}
+		else if (IsSet(supported_opts, SUBOPT_FORCE_ALTER) &&
+				 strcmp(defel->defname, "force_alter") == 0)
+		{
+			if (IsSet(opts->specified_opts, SUBOPT_FORCE_ALTER))
+				errorConflictingDefElem(defel, pstate);
+
+			opts->specified_opts |= SUBOPT_FORCE_ALTER;
+			opts->twophase_force = defGetBoolean(defel);
+		}
 		else
 			ereport(ERROR,
 					(errcode(ERRCODE_SYNTAX_ERROR),
@@ -1148,7 +1161,7 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 								  SUBOPT_DISABLE_ON_ERR |
 								  SUBOPT_PASSWORD_REQUIRED |
 								  SUBOPT_RUN_AS_OWNER | SUBOPT_FAILOVER |
-								  SUBOPT_ORIGIN);
+								  SUBOPT_ORIGIN | SUBOPT_FORCE_ALTER);
 
 				parse_subscription_options(pstate, stmt->options,
 										   supported_opts, &opts);
@@ -1194,6 +1207,16 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 						{
 							ListCell	*cell;
 
+							/*
+							 * Abort prepared transactions if force option is also
+							 * specified. Otherwise raise an ERROR.
+							 */
+							if (!opts.twophase_force)
+								ereport(ERROR,
+										(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+										 errmsg("cannot alter %s when there are prepared transactions",
+												"two_phase = false")));
+
 							/* Abort all listed transactions */
 							foreach(cell, prepared_xacts)
 								FinishPreparedTransaction((char *) lfirst(cell),
@@ -1323,6 +1346,14 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 					replaces[Anum_pg_subscription_suborigin - 1] = true;
 				}
 
+				/* force_alter cannot be used standalone */
+				if (IsSet(opts.specified_opts, SUBOPT_FORCE_ALTER) &&
+					!IsSet(opts.specified_opts, SUBOPT_TWOPHASE_COMMIT))
+					ereport(ERROR,
+							(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+							 errmsg("%s must be specified with %s",
+									"force_alter", "two_phase")));
+
 				update_tuple = true;
 				break;
 			}
diff --git a/src/test/regress/expected/subscription.out b/src/test/regress/expected/subscription.out
index 51fa4b9690..f607045b28 100644
--- a/src/test/regress/expected/subscription.out
+++ b/src/test/regress/expected/subscription.out
@@ -370,6 +370,9 @@ ERROR:  two_phase requires a Boolean value
 CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUBLICATION testpub WITH (connect = false, two_phase = true);
 WARNING:  subscription was created, but is not connected
 HINT:  To initiate replication, you must manually create the replication slot, enable the subscription, and refresh the subscription.
+-- fail - force_alter cannot be set alone
+ALTER SUBSCRIPTION regress_testsub SET (force_alter = true);
+ERROR:  force_alter must be specified with two_phase
 \dRs+
                                                                                                                 List of subscriptions
       Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
diff --git a/src/test/regress/sql/subscription.sql b/src/test/regress/sql/subscription.sql
index a3886d79ca..80ab4dd9bc 100644
--- a/src/test/regress/sql/subscription.sql
+++ b/src/test/regress/sql/subscription.sql
@@ -255,6 +255,9 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 -- now it works
 CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUBLICATION testpub WITH (connect = false, two_phase = true);
 
+-- fail - force_alter cannot be set alone
+ALTER SUBSCRIPTION regress_testsub SET (force_alter = true);
+
 \dRs+
 -- We can alter streaming when two_phase enabled
 ALTER SUBSCRIPTION regress_testsub SET (streaming = true);
diff --git a/src/test/subscription/t/099_twophase_added.pl b/src/test/subscription/t/099_twophase_added.pl
index a8135b671c..7c73a58f2a 100644
--- a/src/test/subscription/t/099_twophase_added.pl
+++ b/src/test/subscription/t/099_twophase_added.pl
@@ -85,16 +85,29 @@ $result = $node_subscriber->safe_psql('postgres',
     "SELECT count(*) FROM pg_prepared_xacts;");
 is($result, q(1), "transaction has been prepared on subscriber");
 
-$node_subscriber->safe_psql(
-    'postgres', "
-    ALTER SUBSCRIPTION sub DISABLE;
-    ALTER SUBSCRIPTION sub SET (two_phase = off);
-    ALTER SUBSCRIPTION sub ENABLE;");
+$node_subscriber->safe_psql('postgres', "ALTER SUBSCRIPTION sub DISABLE;");
+
+my $stdout;
+my $stderr;
+
+($result, $stdout, $stderr) = $node_subscriber->psql(
+	'postgres', "ALTER SUBSCRIPTION sub SET (two_phase = off);");
+ok($stderr =~ /cannot alter two_phase = false when there are prepared transactions/,
+	'ALTER SUBSCRIPTION failed');
+
+$result = $node_subscriber->safe_psql('postgres',
+    "SELECT count(*) FROM pg_prepared_xacts;");
+is($result, q(1), "prepared transaction still exits");
+
+$node_subscriber->safe_psql('postgres',
+    "ALTER SUBSCRIPTION sub SET (two_phase = off, force_alter = on);");
 
 $result = $node_subscriber->safe_psql('postgres',
     "SELECT count(*) FROM pg_prepared_xacts;");
 is($result, q(0), "prepared transaction done by worker is aborted");
 
+$node_subscriber->safe_psql('postgres', "ALTER SUBSCRIPTION sub ENABLE;");
+
 $node_publisher->safe_psql( 'postgres',
     "COMMIT PREPARED 'test_prepared_tab_full';");
 $node_publisher->wait_for_catchup('sub');
-- 
2.43.0

From f7c0476226447793353463b32286410f7b960027 Mon Sep 17 00:00:00 2001
From: Ajin Cherian <ajinc@fast.au.fujitsu.com>
Date: Fri, 5 Apr 2024 06:47:18 -0400
Subject: [PATCH v8 1/4] Allow altering of two_phase option of a SUBSCRIPTION

This patch allows the user to alter the 'two_phase' option of a subscriber provided no
uncommitted prepared transactions are pending on that subscription.

Author: Cherian Ajin, Hayato Kuroda
---
 doc/src/sgml/ref/alter_subscription.sgml      | 12 ++--
 src/backend/access/transam/twophase.c         | 62 ++++++++++++++++
 src/backend/commands/subscriptioncmds.c       | 67 +++++++++++++----
 .../libpqwalreceiver/libpqwalreceiver.c       |  9 +--
 src/backend/replication/logical/launcher.c    | 22 ++++++
 src/backend/replication/logical/worker.c      | 21 +-----
 src/backend/replication/slot.c                | 18 ++++-
 src/backend/replication/walsender.c           | 18 ++++-
 src/bin/psql/tab-complete.c                   |  2 +-
 src/include/access/twophase.h                 |  5 ++
 src/include/replication/slot.h                |  3 +-
 src/include/replication/walreceiver.h         | 11 +--
 src/include/replication/worker_internal.h     |  1 +
 src/test/regress/expected/subscription.out    |  5 +-
 src/test/regress/sql/subscription.sql         |  5 +-
 src/test/subscription/t/021_twophase.pl       | 71 ++++++++++++++++++-
 16 files changed, 269 insertions(+), 63 deletions(-)

diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index a78c1c3a47..88e9a72147 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -68,8 +68,9 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
   <para>
    Commands <command>ALTER SUBSCRIPTION ... REFRESH PUBLICATION</command>,
    <command>ALTER SUBSCRIPTION ... {SET|ADD|DROP} PUBLICATION ...</command>
-   with <literal>refresh</literal> option as <literal>true</literal> and
-   <command>ALTER SUBSCRIPTION ... SET (failover = on|off)</command>
+   with <literal>refresh</literal> option as <literal>true</literal>,
+   <command>ALTER SUBSCRIPTION ... SET (failover = on|off)</command> and
+   <command>ALTER SUBSCRIPTION ... SET (two_phase = on|off)</command>
    cannot be executed inside a transaction block.
 
    These commands also cannot be executed when the subscription has
@@ -228,9 +229,12 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-disable-on-error"><literal>disable_on_error</literal></link>,
       <link linkend="sql-createsubscription-params-with-password-required"><literal>password_required</literal></link>,
       <link linkend="sql-createsubscription-params-with-run-as-owner"><literal>run_as_owner</literal></link>,
-      <link linkend="sql-createsubscription-params-with-origin"><literal>origin</literal></link>, and
-      <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>.
+      <link linkend="sql-createsubscription-params-with-origin"><literal>origin</literal></link>,
+      <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>, and
+      <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>.
       Only a superuser can set <literal>password_required = false</literal>.
+      The <literal>two_phase</literal> parameter can only be altered when the
+      subscription is disabled.
      </para>
 
      <para>
diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index 8090ac9fc1..66fa591eb5 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -2682,3 +2682,65 @@ LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 	LWLockRelease(TwoPhaseStateLock);
 	return found;
 }
+
+/*
+ * TwoPhaseTransactionGid
+ *		Form the prepared transaction GID for two_phase transactions.
+ *
+ * Return the GID in the supplied buffer.
+ */
+void
+TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid, int szgid)
+{
+	Assert(subid != InvalidRepOriginId);
+
+	if (!TransactionIdIsValid(xid))
+		ereport(ERROR,
+				(errcode(ERRCODE_PROTOCOL_VIOLATION),
+				 errmsg_internal("invalid two-phase transaction ID")));
+
+	snprintf(gid, szgid, "pg_gid_%u_%u", subid, xid);
+}
+
+/*
+ * IsTwoPhaseTransactionGidForSubid
+ *		Check whether the given GID (as formed by TwoPhaseTransactionGid) is
+ *		for the specified 'subid'.
+ */
+static bool
+IsTwoPhaseTransactionGidForSubid(Oid subid, char *gid)
+{
+	int				ret;
+	Oid				subid_written;
+	TransactionId	xid;
+
+	ret = sscanf(gid, "pg_gid_%u_%u", &subid_written, &xid);
+
+	return (ret == 2 && subid == subid_written);
+}
+
+/*
+ * LookupGXactBySubid
+ *		Check if the prepared transaction done by apply worker exists.
+ */
+bool
+LookupGXactBySubid(Oid subid)
+{
+	bool		found = false;
+
+	LWLockAcquire(TwoPhaseStateLock, LW_SHARED);
+	for (int i = 0; i < TwoPhaseState->numPrepXacts; i++)
+	{
+		GlobalTransaction gxact = TwoPhaseState->prepXacts[i];
+
+		/* Ignore not-yet-valid GIDs. */
+		if (gxact->valid &&
+			IsTwoPhaseTransactionGidForSubid(subid, gxact->gid))
+		{
+			found = true;
+			break;
+		}
+	}
+	LWLockRelease(TwoPhaseStateLock);
+	return found;
+}
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index e407428dbc..90d967eb7c 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -16,6 +16,7 @@
 
 #include "access/htup_details.h"
 #include "access/table.h"
+#include "access/twophase.h"
 #include "access/xact.h"
 #include "catalog/catalog.h"
 #include "catalog/dependency.h"
@@ -1143,7 +1144,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 			{
 				supported_opts = (SUBOPT_SLOT_NAME |
 								  SUBOPT_SYNCHRONOUS_COMMIT | SUBOPT_BINARY |
-								  SUBOPT_STREAMING | SUBOPT_DISABLE_ON_ERR |
+								  SUBOPT_STREAMING | SUBOPT_TWOPHASE_COMMIT |
+								  SUBOPT_DISABLE_ON_ERR |
 								  SUBOPT_PASSWORD_REQUIRED |
 								  SUBOPT_RUN_AS_OWNER | SUBOPT_FAILOVER |
 								  SUBOPT_ORIGIN);
@@ -1151,6 +1153,52 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 				parse_subscription_options(pstate, stmt->options,
 										   supported_opts, &opts);
 
+				if (IsSet(opts.specified_opts, SUBOPT_TWOPHASE_COMMIT))
+				{
+					/*
+					 * Do not allow changing the two_phase option if the
+					 * subscription is enabled. This is because the two_phase
+					 * option of the slot on the publisher cannot be modified
+					 * if the slot is currently acquired by the apply worker.
+					 */
+					if (form->subenabled)
+						ereport(ERROR,
+								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+								 errmsg("cannot set %s for enabled subscription",
+										"two_phase")));
+
+					/*
+					 * Stop all the subscription workers, just in case. Workers
+					 * may still survive even if the subscription is disabled.
+					 */
+					logicalrep_workers_stop(subid);
+
+					/*
+					 * two_phase cannot be disabled if there are any
+					 * uncommitted prepared transactions present.
+					 */
+					if (!opts.twophase &&
+						form->subtwophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
+						LookupGXactBySubid(subid))
+						ereport(ERROR,
+								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+								 errmsg("cannot disable two_phase when uncommitted prepared transactions present"),
+								 errhint("Resolve these transactions and try again")));
+
+					/*
+					 * The changed two_phase option of the slot can't be rolled
+					 * back.
+					 */
+					PreventInTransactionBlock(isTopLevel, "ALTER SUBSCRIPTION ... SET (two_phase)");
+
+					/* Change system catalog acoordingly */
+					values[Anum_pg_subscription_subtwophasestate - 1] =
+						CharGetDatum(opts.twophase ?
+									 LOGICALREP_TWOPHASE_STATE_PENDING :
+									 LOGICALREP_TWOPHASE_STATE_DISABLED);
+					replaces[Anum_pg_subscription_subtwophasestate - 1] = true;
+				}
+
 				if (IsSet(opts.specified_opts, SUBOPT_SLOT_NAME))
 				{
 					/*
@@ -1505,7 +1553,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 	 * doing the database operations we won't be able to rollback altered
 	 * slot.
 	 */
-	if (replaces[Anum_pg_subscription_subfailover - 1])
+	if (replaces[Anum_pg_subscription_subfailover - 1] ||
+		replaces[Anum_pg_subscription_subtwophasestate - 1])
 	{
 		bool		must_use_password;
 		char	   *err;
@@ -1525,7 +1574,7 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 
 		PG_TRY();
 		{
-			walrcv_alter_slot(wrconn, sub->slotname, opts.failover);
+			walrcv_alter_slot(wrconn, sub->slotname, opts.failover, opts.twophase);
 		}
 		PG_FINALLY();
 		{
@@ -1562,7 +1611,6 @@ DropSubscription(DropSubscriptionStmt *stmt, bool isTopLevel)
 	char	   *subname;
 	char	   *conninfo;
 	char	   *slotname;
-	List	   *subworkers;
 	ListCell   *lc;
 	char		originname[NAMEDATALEN];
 	char	   *err = NULL;
@@ -1672,16 +1720,7 @@ DropSubscription(DropSubscriptionStmt *stmt, bool isTopLevel)
 	 * New workers won't be started because we hold an exclusive lock on the
 	 * subscription till the end of the transaction.
 	 */
-	LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
-	subworkers = logicalrep_workers_find(subid, false);
-	LWLockRelease(LogicalRepWorkerLock);
-	foreach(lc, subworkers)
-	{
-		LogicalRepWorker *w = (LogicalRepWorker *) lfirst(lc);
-
-		logicalrep_worker_stop(w->subid, w->relid);
-	}
-	list_free(subworkers);
+	logicalrep_workers_stop(subid);
 
 	/*
 	 * Remove the no-longer-useful entry in the launcher's table of apply
diff --git a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
index 3c2b1bb496..998bbd517a 100644
--- a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
+++ b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
@@ -80,7 +80,7 @@ static char *libpqrcv_create_slot(WalReceiverConn *conn,
 								  CRSSnapshotAction snapshot_action,
 								  XLogRecPtr *lsn);
 static void libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-								bool failover);
+								bool failover, bool two_phase);
 static pid_t libpqrcv_get_backend_pid(WalReceiverConn *conn);
 static WalRcvExecResult *libpqrcv_exec(WalReceiverConn *conn,
 									   const char *query,
@@ -1121,15 +1121,16 @@ libpqrcv_create_slot(WalReceiverConn *conn, const char *slotname,
  */
 static void
 libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-					bool failover)
+					bool failover, bool two_phase)
 {
 	StringInfoData cmd;
 	PGresult   *res;
 
 	initStringInfo(&cmd);
-	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( FAILOVER %s )",
+	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( FAILOVER %s, TWO_PHASE %s )",
 					 quote_identifier(slotname),
-					 failover ? "true" : "false");
+					 failover ? "true" : "false",
+					 two_phase ? "true" : "false");
 
 	res = libpqrcv_PQexec(conn->streamConn, cmd.data);
 	pfree(cmd.data);
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 66070e9131..548f6e0edb 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -623,6 +623,28 @@ logicalrep_worker_stop(Oid subid, Oid relid)
 	LWLockRelease(LogicalRepWorkerLock);
 }
 
+/*
+ * Stop all the subscription workers.
+ */
+void
+logicalrep_workers_stop(Oid subid)
+{
+	List	   *subworkers;
+	ListCell   *lc;
+
+	LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
+	/* XXX clarify the reason why not only running workers are listed. */
+	subworkers = logicalrep_workers_find(subid, false);
+	LWLockRelease(LogicalRepWorkerLock);
+	foreach(lc, subworkers)
+	{
+		LogicalRepWorker *w = (LogicalRepWorker *) lfirst(lc);
+
+		logicalrep_worker_stop(w->subid, w->relid);
+	}
+	list_free(subworkers);
+}
+
 /*
  * Stop the given logical replication parallel apply worker.
  *
diff --git a/src/backend/replication/logical/worker.c b/src/backend/replication/logical/worker.c
index b5a80fe3e8..dcf656fd45 100644
--- a/src/backend/replication/logical/worker.c
+++ b/src/backend/replication/logical/worker.c
@@ -402,7 +402,6 @@ static void apply_handle_tuple_routing(ApplyExecutionData *edata,
 									   CmdType operation);
 
 /* Compute GID for two_phase transactions */
-static void TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid, int szgid);
 
 /* Functions for skipping changes */
 static void maybe_start_skipping_changes(XLogRecPtr finish_lsn);
@@ -3911,7 +3910,7 @@ maybe_reread_subscription(void)
 	/* !slotname should never happen when enabled is true. */
 	Assert(newsub->slotname);
 
-	/* two-phase should not be altered */
+	/* two-phase cannot be altered while the worker exists */
 	Assert(newsub->twophasestate == MySubscription->twophasestate);
 
 	/*
@@ -4396,24 +4395,6 @@ cleanup_subxact_info()
 	subxact_data.nsubxacts_max = 0;
 }
 
-/*
- * Form the prepared transaction GID for two_phase transactions.
- *
- * Return the GID in the supplied buffer.
- */
-static void
-TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid, int szgid)
-{
-	Assert(subid != InvalidRepOriginId);
-
-	if (!TransactionIdIsValid(xid))
-		ereport(ERROR,
-				(errcode(ERRCODE_PROTOCOL_VIOLATION),
-				 errmsg_internal("invalid two-phase transaction ID")));
-
-	snprintf(gid, szgid, "pg_gid_%u_%u", subid, xid);
-}
-
 /*
  * Common function to run the apply loop with error handling. Disable the
  * subscription, if necessary.
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index aa4ea387da..d0c8d5a4df 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -804,8 +804,10 @@ ReplicationSlotDrop(const char *name, bool nowait)
  * Change the definition of the slot identified by the specified name.
  */
 void
-ReplicationSlotAlter(const char *name, bool failover)
+ReplicationSlotAlter(const char *name, bool failover, bool two_phase)
 {
+	bool		update_slot = false;
+
 	Assert(MyReplicationSlot == NULL);
 
 	ReplicationSlotAcquire(name, false);
@@ -854,6 +856,20 @@ ReplicationSlotAlter(const char *name, bool failover)
 		MyReplicationSlot->data.failover = failover;
 		SpinLockRelease(&MyReplicationSlot->mutex);
 
+		update_slot = true;
+	}
+
+	if (MyReplicationSlot->data.two_phase != two_phase)
+	{
+		SpinLockAcquire(&MyReplicationSlot->mutex);
+		MyReplicationSlot->data.two_phase = two_phase;
+		SpinLockRelease(&MyReplicationSlot->mutex);
+
+		update_slot = true;
+	}
+
+	if (update_slot)
+	{
 		ReplicationSlotMarkDirty();
 		ReplicationSlotSave();
 	}
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index c623b07cf0..2e6ca35049 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1411,9 +1411,11 @@ DropReplicationSlot(DropReplicationSlotCmd *cmd)
  * Process extra options given to ALTER_REPLICATION_SLOT.
  */
 static void
-ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd, bool *failover)
+ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd,
+						  bool *failover, bool *two_phase)
 {
 	bool		failover_given = false;
+	bool		two_phase_given = false;
 
 	/* Parse options */
 	foreach_ptr(DefElem, defel, cmd->options)
@@ -1427,6 +1429,15 @@ ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd, bool *failover)
 			failover_given = true;
 			*failover = defGetBoolean(defel);
 		}
+		else if (strcmp(defel->defname, "two_phase") == 0)
+		{
+			if (two_phase_given)
+				ereport(ERROR,
+						(errcode(ERRCODE_SYNTAX_ERROR),
+						 errmsg("conflicting or redundant options")));
+			two_phase_given = true;
+			*two_phase = defGetBoolean(defel);
+		}
 		else
 			elog(ERROR, "unrecognized option: %s", defel->defname);
 	}
@@ -1439,9 +1450,10 @@ static void
 AlterReplicationSlot(AlterReplicationSlotCmd *cmd)
 {
 	bool		failover = false;
+	bool		two_phase = false;
 
-	ParseAlterReplSlotOptions(cmd, &failover);
-	ReplicationSlotAlter(cmd->slotname, failover);
+	ParseAlterReplSlotOptions(cmd, &failover, &two_phase);
+	ReplicationSlotAlter(cmd->slotname, failover, two_phase);
 }
 
 /*
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
index d453e224d9..891face1b6 100644
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -1948,7 +1948,7 @@ psql_completion(const char *text, int start, int end)
 	else if (HeadMatches("ALTER", "SUBSCRIPTION", MatchAny) && TailMatches("SET", "("))
 		COMPLETE_WITH("binary", "disable_on_error", "failover", "origin",
 					  "password_required", "run_as_owner", "slot_name",
-					  "streaming", "synchronous_commit");
+					  "streaming", "synchronous_commit", "two_phase");
 	/* ALTER SUBSCRIPTION <name> SKIP ( */
 	else if (HeadMatches("ALTER", "SUBSCRIPTION", MatchAny) && TailMatches("SKIP", "("))
 		COMPLETE_WITH("lsn");
diff --git a/src/include/access/twophase.h b/src/include/access/twophase.h
index 56248c0006..d37e06fdee 100644
--- a/src/include/access/twophase.h
+++ b/src/include/access/twophase.h
@@ -62,4 +62,9 @@ extern void PrepareRedoRemove(TransactionId xid, bool giveWarning);
 extern void restoreTwoPhaseData(void);
 extern bool LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 						TimestampTz origin_prepare_timestamp);
+
+extern void TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid,
+								   int szgid);
+extern bool LookupGXactBySubid(Oid subid);
+
 #endif							/* TWOPHASE_H */
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 1bc80960ef..014e216cf5 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -243,7 +243,8 @@ extern void ReplicationSlotCreate(const char *name, bool db_specific,
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
 extern void ReplicationSlotDropAcquired(void);
-extern void ReplicationSlotAlter(const char *name, bool failover);
+extern void ReplicationSlotAlter(const char *name, bool failover,
+								 bool two_phase);
 
 extern void ReplicationSlotAcquire(const char *name, bool nowait);
 extern void ReplicationSlotRelease(void);
diff --git a/src/include/replication/walreceiver.h b/src/include/replication/walreceiver.h
index 12f71fa99b..31fa1257ec 100644
--- a/src/include/replication/walreceiver.h
+++ b/src/include/replication/walreceiver.h
@@ -372,12 +372,13 @@ typedef char *(*walrcv_create_slot_fn) (WalReceiverConn *conn,
 /*
  * walrcv_alter_slot_fn
  *
- * Change the definition of a replication slot. Currently, it only supports
- * changing the failover property of the slot.
+ * Change the definition of a replication slot. Currently, it supports
+ * changing the failover and the two_phase property of the slot.
  */
 typedef void (*walrcv_alter_slot_fn) (WalReceiverConn *conn,
 									  const char *slotname,
-									  bool failover);
+									  bool failover,
+									  bool two_phase);
 
 /*
  * walrcv_get_backend_pid_fn
@@ -455,8 +456,8 @@ extern PGDLLIMPORT WalReceiverFunctionsType *WalReceiverFunctions;
 	WalReceiverFunctions->walrcv_send(conn, buffer, nbytes)
 #define walrcv_create_slot(conn, slotname, temporary, two_phase, failover, snapshot_action, lsn) \
 	WalReceiverFunctions->walrcv_create_slot(conn, slotname, temporary, two_phase, failover, snapshot_action, lsn)
-#define walrcv_alter_slot(conn, slotname, failover) \
-	WalReceiverFunctions->walrcv_alter_slot(conn, slotname, failover)
+#define walrcv_alter_slot(conn, slotname, failover, two_phase) \
+	WalReceiverFunctions->walrcv_alter_slot(conn, slotname, failover, two_phase)
 #define walrcv_get_backend_pid(conn) \
 	WalReceiverFunctions->walrcv_get_backend_pid(conn)
 #define walrcv_exec(conn, exec, nRetTypes, retTypes) \
diff --git a/src/include/replication/worker_internal.h b/src/include/replication/worker_internal.h
index 515aefd519..d5428263c1 100644
--- a/src/include/replication/worker_internal.h
+++ b/src/include/replication/worker_internal.h
@@ -246,6 +246,7 @@ extern bool logicalrep_worker_launch(LogicalRepWorkerType wtype,
 									 Oid userid, Oid relid,
 									 dsm_handle subworker_dsm);
 extern void logicalrep_worker_stop(Oid subid, Oid relid);
+extern void logicalrep_workers_stop(Oid subid);
 extern void logicalrep_pa_worker_stop(ParallelApplyWorkerInfo *winfo);
 extern void logicalrep_worker_wakeup(Oid subid, Oid relid);
 extern void logicalrep_worker_wakeup_ptr(LogicalRepWorker *worker);
diff --git a/src/test/regress/expected/subscription.out b/src/test/regress/expected/subscription.out
index 0f2a25cdc1..51fa4b9690 100644
--- a/src/test/regress/expected/subscription.out
+++ b/src/test/regress/expected/subscription.out
@@ -377,10 +377,7 @@ HINT:  To initiate replication, you must manually create the replication slot, e
  regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | p                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
---fail - alter of two_phase option not supported.
-ALTER SUBSCRIPTION regress_testsub SET (two_phase = false);
-ERROR:  unrecognized subscription parameter: "two_phase"
--- but can alter streaming when two_phase enabled
+-- We can alter streaming when two_phase enabled
 ALTER SUBSCRIPTION regress_testsub SET (streaming = true);
 \dRs+
                                                                                                                 List of subscriptions
diff --git a/src/test/regress/sql/subscription.sql b/src/test/regress/sql/subscription.sql
index 3e5ba4cb8c..a3886d79ca 100644
--- a/src/test/regress/sql/subscription.sql
+++ b/src/test/regress/sql/subscription.sql
@@ -256,10 +256,7 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUBLICATION testpub WITH (connect = false, two_phase = true);
 
 \dRs+
---fail - alter of two_phase option not supported.
-ALTER SUBSCRIPTION regress_testsub SET (two_phase = false);
-
--- but can alter streaming when two_phase enabled
+-- We can alter streaming when two_phase enabled
 ALTER SUBSCRIPTION regress_testsub SET (streaming = true);
 
 \dRs+
diff --git a/src/test/subscription/t/021_twophase.pl b/src/test/subscription/t/021_twophase.pl
index 9437cd4c3b..72df258000 100644
--- a/src/test/subscription/t/021_twophase.pl
+++ b/src/test/subscription/t/021_twophase.pl
@@ -367,6 +367,75 @@ $result =
   $node_subscriber->safe_psql('postgres', "SELECT count(*) FROM tab_copy;");
 is($result, qq(2), 'replicated data in subscriber table');
 
+# Clean up
+$node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub");
+
+###############################
+# Disable the subscription and alter it to two_phase = false,
+# then verify that the altered subscription reflects the two_phase option.
+###############################
+
+# Alter subscription two_phase to false
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy DISABLE");
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = false)");
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy ENABLE");
+
+# Wait for subscription startup
+$node_subscriber->wait_for_subscription_sync($node_publisher, $appname_copy);
+
+# Make sure that the two-phase is disabled on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+       "SELECT subtwophasestate FROM pg_subscription WHERE subname = 'tap_sub_copy';"
+);
+is($result, qq(d), 'two-phase should be disabled');
+
+# Now do a prepare on the publisher and make sure that it is not replicated.
+$node_publisher->safe_psql(
+       'postgres', qq{
+    BEGIN;
+    INSERT INTO tab_copy VALUES (100);
+    PREPARE TRANSACTION 'newgid';
+	});
+
+# Wait for the subscriber to catchup
+$node_publisher->wait_for_catchup($appname_copy);
+
+# Make sure there are no prepared transactions on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT count(*) FROM pg_prepared_xacts;");
+is($result, qq(0), 'should be no prepared transactions on subscriber');
+
+# Now commit the insert and verify that it IS replicated
+$node_publisher->safe_psql('postgres', "COMMIT PREPARED 'newgid';");
+
+# Wait for the subscriber to catchup
+$node_publisher->wait_for_catchup($appname_copy);
+
+# Make sure that the committed transaction is replicated.
+$result =
+	$node_subscriber->safe_psql('postgres', "SELECT count(*) FROM tab_copy;");
+is($result, qq(3), 'replicated data in subscriber table');
+
+# Alter subscription two_phase to true
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy DISABLE");
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = true)");
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy ENABLE");
+
+# Wait for subscription startup
+$node_subscriber->wait_for_subscription_sync($node_publisher, $appname_copy);
+
+# Make sure that the two-phase is enabled on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT subtwophasestate FROM pg_subscription WHERE subname = 'tap_sub_copy';"
+);
+is($result, qq(e), 'two-phase should be enabled');
+
 $node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub_copy;");
 $node_publisher->safe_psql('postgres', "DROP PUBLICATION tap_pub_copy;");
 
@@ -374,8 +443,6 @@ $node_publisher->safe_psql('postgres', "DROP PUBLICATION tap_pub_copy;");
 # check all the cleanup
 ###############################
 
-$node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub");
-
 $result = $node_subscriber->safe_psql('postgres',
 	"SELECT count(*) FROM pg_subscription");
 is($result, qq(0), 'check subscription was dropped on subscriber');
-- 
2.43.0

From b3853307efcdbee2c9053688b3860f0b2347462b Mon Sep 17 00:00:00 2001
From: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Date: Wed, 17 Apr 2024 06:18:23 +0000
Subject: [PATCH v8 2/4] Alter slot option two_phase only when altering "on" to
 "off"

Since the two_phase option is controlled by both the publisher (as a slot option)
and the subscriber (as a subscription option), the slot option must also be
modified.

Regarding the off->on case, the logical replication already has a mechanism for
it, so there is no need to do anything special for the on->off case; however,
we must connect to the publisher and expressly change the parameter. The
operation cannot be rolled back, and altering the parameter from "on" to "off"
within a transaction is prohibited.
---
 doc/src/sgml/ref/alter_subscription.sgml      |  2 +-
 src/backend/commands/subscriptioncmds.c       | 30 ++++--
 .../libpqwalreceiver/libpqwalreceiver.c       | 23 +++--
 src/include/replication/walreceiver.h         |  5 +-
 src/test/subscription/meson.build             |  1 +
 src/test/subscription/t/099_twophase_added.pl | 95 +++++++++++++++++++
 6 files changed, 140 insertions(+), 16 deletions(-)
 create mode 100644 src/test/subscription/t/099_twophase_added.pl

diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index 88e9a72147..0c2894a94e 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -70,7 +70,7 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
    <command>ALTER SUBSCRIPTION ... {SET|ADD|DROP} PUBLICATION ...</command>
    with <literal>refresh</literal> option as <literal>true</literal>,
    <command>ALTER SUBSCRIPTION ... SET (failover = on|off)</command> and
-   <command>ALTER SUBSCRIPTION ... SET (two_phase = on|off)</command>
+   <command>ALTER SUBSCRIPTION ... SET (two_phase = off)</command>
    cannot be executed inside a transaction block.
 
    These commands also cannot be executed when the subscription has
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index 90d967eb7c..6b2cb71dac 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -1097,6 +1097,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 	Form_pg_subscription form;
 	bits32		supported_opts;
 	SubOpts		opts = {0};
+	bool		update_failover;
+	bool		update_two_phase;
 
 	rel = table_open(SubscriptionRelationId, RowExclusiveLock);
 
@@ -1186,10 +1188,14 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 								 errhint("Resolve these transactions and try again")));
 
 					/*
-					 * The changed two_phase option of the slot can't be rolled
-					 * back.
+					 * Since the altering two_phase option of subscriptions
+					 * also leads to the change of slot option, this command
+					 * cannot be rolled back. So prevent we are in the
+					 * transaction block.
 					 */
-					PreventInTransactionBlock(isTopLevel, "ALTER SUBSCRIPTION ... SET (two_phase)");
+					if (!opts.twophase)
+						PreventInTransactionBlock(isTopLevel,
+												  "ALTER SUBSCRIPTION ... SET (two_phase = off)");
 
 					/* Change system catalog acoordingly */
 					values[Anum_pg_subscription_subtwophasestate - 1] =
@@ -1547,14 +1553,22 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 	}
 
 	/*
-	 * Try to acquire the connection necessary for altering slot.
+	 * Check the need to alter the replication slot. Failover and two_phase
+	 * options are controlled by both the publisher (as a slot option) and the
+	 * subscriber (as a subscription option).
+	 */
+	update_failover = replaces[Anum_pg_subscription_subfailover - 1];
+	update_two_phase = (replaces[Anum_pg_subscription_subtwophasestate - 1] &&
+						!opts.twophase);
+
+	/*
+	 * Try to acquire the connection necessary for altering slot, if needed.
 	 *
 	 * This has to be at the end because otherwise if there is an error while
 	 * doing the database operations we won't be able to rollback altered
 	 * slot.
 	 */
-	if (replaces[Anum_pg_subscription_subfailover - 1] ||
-		replaces[Anum_pg_subscription_subtwophasestate - 1])
+	if (update_failover || update_two_phase)
 	{
 		bool		must_use_password;
 		char	   *err;
@@ -1574,7 +1588,9 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 
 		PG_TRY();
 		{
-			walrcv_alter_slot(wrconn, sub->slotname, opts.failover, opts.twophase);
+			walrcv_alter_slot(wrconn, sub->slotname,
+							  update_failover ? &opts.failover : NULL,
+							  update_two_phase ? &opts.twophase : NULL);
 		}
 		PG_FINALLY();
 		{
diff --git a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
index 998bbd517a..2800597f4c 100644
--- a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
+++ b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
@@ -80,7 +80,7 @@ static char *libpqrcv_create_slot(WalReceiverConn *conn,
 								  CRSSnapshotAction snapshot_action,
 								  XLogRecPtr *lsn);
 static void libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-								bool failover, bool two_phase);
+								const bool *failover, const bool *two_phase);
 static pid_t libpqrcv_get_backend_pid(WalReceiverConn *conn);
 static WalRcvExecResult *libpqrcv_exec(WalReceiverConn *conn,
 									   const char *query,
@@ -1121,16 +1121,27 @@ libpqrcv_create_slot(WalReceiverConn *conn, const char *slotname,
  */
 static void
 libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-					bool failover, bool two_phase)
+					const bool *failover, const bool *two_phase)
 {
 	StringInfoData cmd;
 	PGresult   *res;
 
 	initStringInfo(&cmd);
-	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( FAILOVER %s, TWO_PHASE %s )",
-					 quote_identifier(slotname),
-					 failover ? "true" : "false",
-					 two_phase ? "true" : "false");
+	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( ",
+					 quote_identifier(slotname));
+
+	if (failover)
+		appendStringInfo(&cmd, "FAILOVER %s",
+						 *failover ? "true" : "false");
+
+	if (failover && two_phase)
+		appendStringInfo(&cmd, ", ");
+
+	if (two_phase)
+		appendStringInfo(&cmd, "TWO_PHASE %s",
+						 *two_phase ? "true" : "false");
+
+	appendStringInfoString(&cmd, ");");
 
 	res = libpqrcv_PQexec(conn->streamConn, cmd.data);
 	pfree(cmd.data);
diff --git a/src/include/replication/walreceiver.h b/src/include/replication/walreceiver.h
index 31fa1257ec..7ffa5a58b3 100644
--- a/src/include/replication/walreceiver.h
+++ b/src/include/replication/walreceiver.h
@@ -377,8 +377,9 @@ typedef char *(*walrcv_create_slot_fn) (WalReceiverConn *conn,
  */
 typedef void (*walrcv_alter_slot_fn) (WalReceiverConn *conn,
 									  const char *slotname,
-									  bool failover,
-									  bool two_phase);
+									  const bool *failover,
+									  const bool *two_phase);
+
 
 /*
  * walrcv_get_backend_pid_fn
diff --git a/src/test/subscription/meson.build b/src/test/subscription/meson.build
index c591cd7d61..b4bd522c3d 100644
--- a/src/test/subscription/meson.build
+++ b/src/test/subscription/meson.build
@@ -40,6 +40,7 @@ tests += {
       't/031_column_list.pl',
       't/032_subscribe_use_index.pl',
       't/033_run_as_table_owner.pl',
+      't/099_twophase_added.pl',
       't/100_bugs.pl',
     ],
   },
diff --git a/src/test/subscription/t/099_twophase_added.pl b/src/test/subscription/t/099_twophase_added.pl
new file mode 100644
index 0000000000..62f4acad27
--- /dev/null
+++ b/src/test/subscription/t/099_twophase_added.pl
@@ -0,0 +1,95 @@
+# Copyright (c) 2024, PostgreSQL Global Development Group
+
+# Additional tests for altering two_phase option
+use strict;
+use warnings FATAL => 'all';
+use PostgreSQL::Test::Cluster;
+use PostgreSQL::Test::Utils;
+use Test::More;
+
+# Initialize publisher node
+my $node_publisher = PostgreSQL::Test::Cluster->new('publisher');
+$node_publisher->init(allows_streaming => 'logical');
+$node_publisher->append_conf('postgresql.conf',
+	qq(max_prepared_transactions = 10));
+$node_publisher->start;
+
+# Create subscriber node
+my $node_subscriber = PostgreSQL::Test::Cluster->new('subscriber');
+$node_subscriber->init;
+$node_subscriber->append_conf('postgresql.conf',
+	qq(max_prepared_transactions = 10
+	log_min_messages = debug1));
+$node_subscriber->start;
+
+# Define tables on both nodes
+$node_publisher->safe_psql('postgres',
+    "CREATE TABLE tab_full (a int PRIMARY KEY);");
+$node_subscriber->safe_psql('postgres',
+	"CREATE TABLE tab_full (a int PRIMARY KEY)");
+
+# Setup logical replication, with two_phase = "off"
+my $publisher_connstr = $node_publisher->connstr . ' dbname=postgres';
+$node_publisher->safe_psql('postgres',
+	"CREATE PUBLICATION pub FOR ALL TABLES");
+
+my $log_offset = -s $node_subscriber->logfile;
+
+$node_subscriber->safe_psql(
+	'postgres', "
+	CREATE SUBSCRIPTION regress_sub
+	CONNECTION '$publisher_connstr' PUBLICATION pub
+	WITH (two_phase = off, copy_data = off, failover = off)");
+
+# Verify the started worker recognized two_phase was disabled
+$node_subscriber->wait_for_log(
+	'logical replication apply worker for subscription "regress_sub" two_phase is DISABLED', $log_offset);
+
+# Check the case that prepared transactions exist on the publisher node.
+#
+# Since the two_phase is "off", then normally, this PREPARE will do nothing
+# until the COMMIT PREPARED, but in this test, we toggle the two_phase to "on"
+# again before the COMMIT PREPARED happens.
+
+# Prepare a transaction to insert some tuples into the table
+$node_publisher->safe_psql(
+	'postgres', "
+	BEGIN;
+	INSERT INTO tab_full VALUES (generate_series(1, 5));
+	PREPARE TRANSACTION 'test_prepared_tab_full';");
+
+$node_publisher->wait_for_catchup('regress_sub');
+
+# Verify the prepared transaction is not yet replicated to the subscriber
+# because two_phase is set to "off".
+my $result = $node_subscriber->safe_psql('postgres',
+    "SELECT count(*) FROM pg_prepared_xacts;");
+is($result, q(0), "transaction is not prepared on subscriber");
+
+$log_offset = -s $node_subscriber->logfile;
+
+# Toggle the two_phase to "on" *before* the COMMIT PREPARED. Since we are the
+# special path for the case where both two_phase and failover are altered, it
+# is also set to "on".
+$node_subscriber->safe_psql(
+    'postgres', "
+    ALTER SUBSCRIPTION regress_sub DISABLE;
+    ALTER SUBSCRIPTION regress_sub SET (two_phase = on, failover = on);
+    ALTER SUBSCRIPTION regress_sub ENABLE;");
+
+# Verify the started worker recognized two_phase was enabled
+$node_subscriber->wait_for_log(
+	'logical replication apply worker for subscription "regress_sub" two_phase is ENABLED', $log_offset);
+
+# And do COMMIT PREPARED the prepared transaction
+$node_publisher->safe_psql('postgres',
+    "COMMIT PREPARED 'test_prepared_tab_full';");
+$node_publisher->wait_for_catchup('regress_sub');
+
+# Verify inserted tuples are replicated
+$result = $node_subscriber->safe_psql('postgres',
+    "SELECT count(*) FROM tab_full;");
+is($result, q(5),
+   "prepared transactions done before altering can be replicated");
+
+done_testing();
-- 
2.43.0

From d4d4503ea12bfd23325e78c8f2b75016f4c163c7 Mon Sep 17 00:00:00 2001
From: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Date: Mon, 8 Apr 2024 12:39:12 +0000
Subject: [PATCH v8 3/4] Abort prepared transactions while altering two_phase
 to off

If we alter the two_phase parameter from "on" to "off" and there are prepared
transactions on the subscriber, they won't be resolved. To avoid this issue, we
allow the backend to abort all prepared transactions while altering the
subscription.
---
 doc/src/sgml/ref/alter_subscription.sgml      |  9 +++-
 src/backend/access/transam/twophase.c         | 17 +++----
 src/backend/commands/subscriptioncmds.c       | 43 +++++++++++-------
 src/include/access/twophase.h                 |  3 +-
 src/test/subscription/t/099_twophase_added.pl | 44 +++++++++++++++++++
 5 files changed, 87 insertions(+), 29 deletions(-)

diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index 0c2894a94e..e81661aa04 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -233,8 +233,6 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>, and
       <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>.
       Only a superuser can set <literal>password_required = false</literal>.
-      The <literal>two_phase</literal> parameter can only be altered when the
-      subscription is disabled.
      </para>
 
      <para>
@@ -256,6 +254,13 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>
       option is enabled.
      </para>
+
+     <para>
+      The <literal>two_phase</literal> parameter can only be altered when the
+      subscription is disabled. When altering the parameter from <literal>on</literal>
+      to <literal>off</literal>, the backend process checks prepared
+      transactions done by the logical replication worker and aborts them.
+     </para>
     </listitem>
    </varlistentry>
 
diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index 66fa591eb5..f384bd8c0a 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -2720,13 +2720,13 @@ IsTwoPhaseTransactionGidForSubid(Oid subid, char *gid)
 }
 
 /*
- * LookupGXactBySubid
- *		Check if the prepared transaction done by apply worker exists.
+ * GetGidListBySubid
+ *      Get a list of GIDs which is PREPARE'd by the given subscription.
  */
-bool
-LookupGXactBySubid(Oid subid)
+List *
+GetGidListBySubid(Oid subid)
 {
-	bool		found = false;
+	List *list = NIL;
 
 	LWLockAcquire(TwoPhaseStateLock, LW_SHARED);
 	for (int i = 0; i < TwoPhaseState->numPrepXacts; i++)
@@ -2736,11 +2736,8 @@ LookupGXactBySubid(Oid subid)
 		/* Ignore not-yet-valid GIDs. */
 		if (gxact->valid &&
 			IsTwoPhaseTransactionGidForSubid(subid, gxact->gid))
-		{
-			found = true;
-			break;
-		}
+			list = lappend(list, pstrdup(gxact->gid));
 	}
 	LWLockRelease(TwoPhaseStateLock);
-	return found;
+	return list;
 }
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index 6b2cb71dac..cabbf9eab9 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -1176,27 +1176,38 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 					logicalrep_workers_stop(subid);
 
 					/*
-					 * two_phase cannot be disabled if there are any
-					 * uncommitted prepared transactions present.
-					 */
-					if (!opts.twophase &&
-						form->subtwophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
-						LookupGXactBySubid(subid))
-						ereport(ERROR,
-								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-								 errmsg("cannot disable two_phase when uncommitted prepared transactions present"),
-								 errhint("Resolve these transactions and try again")));
-
-					/*
-					 * Since the altering two_phase option of subscriptions
-					 * also leads to the change of slot option, this command
-					 * cannot be rolled back. So prevent we are in the
-					 * transaction block.
+					 * If two_phase was enabled, there is a possibility the
+					 * transactions has already been PREPARE'd. They must be
+					 * checked and rolled back.
 					 */
 					if (!opts.twophase)
+					{
+						List *prepared_xacts;
+
+						/*
+						 * Since the altering two_phase option of subscriptions
+						 * (especially on->off case) also leads to the
+						 * change of slot option, this command cannot be rolled
+						 * back. So prevent we are in the transaction block.
+						 */
 						PreventInTransactionBlock(isTopLevel,
 												  "ALTER SUBSCRIPTION ... SET (two_phase = off)");
 
+						/*
+						 * To prevent prepared transactions from being
+						 * isolated, they must manually be aborted.
+						 */
+						if (sub->twophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
+							(prepared_xacts = GetGidListBySubid(subid)) != NIL)
+						{
+							/* Abort all listed transactions */
+							foreach_ptr(char, gid, prepared_xacts)
+								FinishPreparedTransaction(gid, false);
+
+							list_free_deep(prepared_xacts);
+						}
+					}
+
 					/* Change system catalog acoordingly */
 					values[Anum_pg_subscription_subtwophasestate - 1] =
 						CharGetDatum(opts.twophase ?
diff --git a/src/include/access/twophase.h b/src/include/access/twophase.h
index d37e06fdee..f7a5cf0c12 100644
--- a/src/include/access/twophase.h
+++ b/src/include/access/twophase.h
@@ -18,6 +18,7 @@
 #include "access/xlogdefs.h"
 #include "datatype/timestamp.h"
 #include "storage/lock.h"
+#include "nodes/pg_list.h"
 
 /*
  * GlobalTransactionData is defined in twophase.c; other places have no
@@ -65,6 +66,6 @@ extern bool LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 
 extern void TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid,
 								   int szgid);
-extern bool LookupGXactBySubid(Oid subid);
+extern List *GetGidListBySubid(Oid subid);
 
 #endif							/* TWOPHASE_H */
diff --git a/src/test/subscription/t/099_twophase_added.pl b/src/test/subscription/t/099_twophase_added.pl
index 62f4acad27..59baa3eadc 100644
--- a/src/test/subscription/t/099_twophase_added.pl
+++ b/src/test/subscription/t/099_twophase_added.pl
@@ -92,4 +92,48 @@ $result = $node_subscriber->safe_psql('postgres',
 is($result, q(5),
    "prepared transactions done before altering can be replicated");
 
+# Check the case that prepared transactions exist on the subscriber node
+#
+# If the two_phase is altering from "on" to "off" and there are prepared
+# transactions on the subscriber, they must be aborted. This test checks it.
+
+# Prepare a transaction to insert some tuples into the table
+$node_publisher->safe_psql(
+	'postgres', "
+	BEGIN;
+	INSERT INTO tab_full VALUES (generate_series(6, 10));
+	PREPARE TRANSACTION 'test_prepared_tab_full';");
+
+$node_publisher->wait_for_catchup('regress_sub');
+
+# Verify the prepared transaction has been replicated to the subscriber because
+# two_phase is set to "on".
+$result = $node_subscriber->safe_psql('postgres',
+    "SELECT count(*) FROM pg_prepared_xacts;");
+is($result, q(1), "transaction has been prepared on subscriber");
+
+# Toggle the two_phase to "off" before the COMMIT PREPARED
+$node_subscriber->safe_psql(
+    'postgres', "
+    ALTER SUBSCRIPTION regress_sub DISABLE;
+    ALTER SUBSCRIPTION regress_sub SET (two_phase = off);
+    ALTER SUBSCRIPTION regress_sub ENABLE;");
+
+# Verify the prepared transaction are aborted because two_phase is changed to
+# "off".
+$result = $node_subscriber->safe_psql('postgres',
+    "SELECT count(*) FROM pg_prepared_xacts;");
+is($result, q(0), "prepared transaction done by worker is aborted");
+
+# Do COMMIT PREPARED the prepared transaction
+$node_publisher->safe_psql( 'postgres',
+    "COMMIT PREPARED 'test_prepared_tab_full';");
+$node_publisher->wait_for_catchup('regress_sub');
+
+# Verify inserted tuples are replicated
+$result = $node_subscriber->safe_psql('postgres',
+    "SELECT count(10) FROM tab_full;");
+is($result, q(10),
+   "prepared transactions on publisher can be replicated");
+
 done_testing();
-- 
2.43.0

From 0ed818f49046ec06c5d2f56928fd1a672892c6b8 Mon Sep 17 00:00:00 2001
From: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Date: Fri, 19 Apr 2024 11:03:19 +0000
Subject: [PATCH v8 4/4] Add force_alter option for ALTER SUBSCIRPTION ... SET
 command

Previously, all prepared transactions on the standby were rolled back when
toggling two_phase from "on" to "off". However, this operation may not be
expected by users. To ensure users understand what happens, we added the
"force_alter" parameter. When two_phase is toggling to "off", and there are
prepared transactions, they will be aborted only when "force_alter" is set to
true. Otherwise, an ERROR occurs.
---
 doc/src/sgml/ref/alter_subscription.sgml      |  9 ++--
 src/backend/commands/subscriptioncmds.c       | 28 ++++++++++++-
 src/test/regress/expected/subscription.out    |  3 ++
 src/test/regress/sql/subscription.sql         |  3 ++
 src/test/subscription/t/099_twophase_added.pl | 42 +++++++++++++++----
 5 files changed, 72 insertions(+), 13 deletions(-)

diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index e81661aa04..1324d6390a 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -257,9 +257,12 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
 
      <para>
       The <literal>two_phase</literal> parameter can only be altered when the
-      subscription is disabled. When altering the parameter from <literal>on</literal>
-      to <literal>off</literal>, the backend process checks prepared
-      transactions done by the logical replication worker and aborts them.
+      subscription is disabled. Altering the parameter from <literal>on</literal>
+      to <literal>off</literal> will be failed when there are prepared
+      transactions done by the logical replication worker. If you want to alter
+      the parameter forcibly in this case, <literal>force_alter</literal>
+      option must be set to <literal>on</literal> at the same time. If
+      specified, the backend process aborts prepared transactions.
      </para>
     </listitem>
    </varlistentry>
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index cabbf9eab9..8b4ea403a0 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -73,6 +73,7 @@
 #define SUBOPT_FAILOVER				0x00002000
 #define SUBOPT_LSN					0x00004000
 #define SUBOPT_ORIGIN				0x00008000
+#define SUBOPT_FORCE_ALTER			0x00010000
 
 /* check if the 'val' has 'bits' set */
 #define IsSet(val, bits)  (((val) & (bits)) == (bits))
@@ -100,6 +101,7 @@ typedef struct SubOpts
 	bool		failover;
 	char	   *origin;
 	XLogRecPtr	lsn;
+	bool		force_alter;
 } SubOpts;
 
 static List *fetch_table_list(WalReceiverConn *wrconn, List *publications);
@@ -162,6 +164,8 @@ parse_subscription_options(ParseState *pstate, List *stmt_options,
 		opts->failover = false;
 	if (IsSet(supported_opts, SUBOPT_ORIGIN))
 		opts->origin = pstrdup(LOGICALREP_ORIGIN_ANY);
+	if (IsSet(supported_opts, SUBOPT_FORCE_ALTER))
+		opts->force_alter = false;
 
 	/* Parse options */
 	foreach(lc, stmt_options)
@@ -367,6 +371,15 @@ parse_subscription_options(ParseState *pstate, List *stmt_options,
 			opts->specified_opts |= SUBOPT_LSN;
 			opts->lsn = lsn;
 		}
+		else if (IsSet(supported_opts, SUBOPT_FORCE_ALTER) &&
+				 strcmp(defel->defname, "force_alter") == 0)
+		{
+			if (IsSet(opts->specified_opts, SUBOPT_FORCE_ALTER))
+				errorConflictingDefElem(defel, pstate);
+
+			opts->specified_opts |= SUBOPT_FORCE_ALTER;
+			opts->force_alter = defGetBoolean(defel);
+		}
 		else
 			ereport(ERROR,
 					(errcode(ERRCODE_SYNTAX_ERROR),
@@ -1150,7 +1163,7 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 								  SUBOPT_DISABLE_ON_ERR |
 								  SUBOPT_PASSWORD_REQUIRED |
 								  SUBOPT_RUN_AS_OWNER | SUBOPT_FAILOVER |
-								  SUBOPT_ORIGIN);
+								  SUBOPT_ORIGIN | SUBOPT_FORCE_ALTER);
 
 				parse_subscription_options(pstate, stmt->options,
 										   supported_opts, &opts);
@@ -1200,6 +1213,19 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 						if (sub->twophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
 							(prepared_xacts = GetGidListBySubid(subid)) != NIL)
 						{
+							/*
+							 * Abort prepared transactions only if
+							 * 'force_alter' option is true. Otherwise raise
+							 * an ERROR.
+							 */
+							if (!opts.force_alter)
+								ereport(ERROR,
+										(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+										 errmsg("cannot alter %s when there are prepared transactions",
+												"two_phase = off"),
+										 errhint("Resolve these transactions or set %s at the same time, and then try again.",
+												 "force_alter = true")));
+
 							/* Abort all listed transactions */
 							foreach_ptr(char, gid, prepared_xacts)
 								FinishPreparedTransaction(gid, false);
diff --git a/src/test/regress/expected/subscription.out b/src/test/regress/expected/subscription.out
index 51fa4b9690..f607045b28 100644
--- a/src/test/regress/expected/subscription.out
+++ b/src/test/regress/expected/subscription.out
@@ -370,6 +370,9 @@ ERROR:  two_phase requires a Boolean value
 CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUBLICATION testpub WITH (connect = false, two_phase = true);
 WARNING:  subscription was created, but is not connected
 HINT:  To initiate replication, you must manually create the replication slot, enable the subscription, and refresh the subscription.
+-- fail - force_alter cannot be set alone
+ALTER SUBSCRIPTION regress_testsub SET (force_alter = true);
+ERROR:  force_alter must be specified with two_phase
 \dRs+
                                                                                                                 List of subscriptions
       Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
diff --git a/src/test/regress/sql/subscription.sql b/src/test/regress/sql/subscription.sql
index a3886d79ca..80ab4dd9bc 100644
--- a/src/test/regress/sql/subscription.sql
+++ b/src/test/regress/sql/subscription.sql
@@ -255,6 +255,9 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 -- now it works
 CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUBLICATION testpub WITH (connect = false, two_phase = true);
 
+-- fail - force_alter cannot be set alone
+ALTER SUBSCRIPTION regress_testsub SET (force_alter = true);
+
 \dRs+
 -- We can alter streaming when two_phase enabled
 ALTER SUBSCRIPTION regress_testsub SET (streaming = true);
diff --git a/src/test/subscription/t/099_twophase_added.pl b/src/test/subscription/t/099_twophase_added.pl
index 59baa3eadc..c826881802 100644
--- a/src/test/subscription/t/099_twophase_added.pl
+++ b/src/test/subscription/t/099_twophase_added.pl
@@ -95,7 +95,8 @@ is($result, q(5),
 # Check the case that prepared transactions exist on the subscriber node
 #
 # If the two_phase is altering from "on" to "off" and there are prepared
-# transactions on the subscriber, they must be aborted. This test checks it.
+# transactions on the subscriber, we must error out or abort all prepared
+# transactions. Below part checks both cases.
 
 # Prepare a transaction to insert some tuples into the table
 $node_publisher->safe_psql(
@@ -112,15 +113,38 @@ $result = $node_subscriber->safe_psql('postgres',
     "SELECT count(*) FROM pg_prepared_xacts;");
 is($result, q(1), "transaction has been prepared on subscriber");
 
-# Toggle the two_phase to "off" before the COMMIT PREPARED
-$node_subscriber->safe_psql(
-    'postgres', "
-    ALTER SUBSCRIPTION regress_sub DISABLE;
-    ALTER SUBSCRIPTION regress_sub SET (two_phase = off);
-    ALTER SUBSCRIPTION regress_sub ENABLE;");
 
-# Verify the prepared transaction are aborted because two_phase is changed to
-# "off".
+# Disable the subscription to alter the two_phase option
+$node_subscriber->safe_psql('postgres', "ALTER SUBSCRIPTION regress_sub DISABLE;");
+
+# Try altering the two_phase option to "off." The command will fail since there
+# is a prepared transaction and the force option is not specified.
+my $stdout;
+my $stderr;
+
+($result, $stdout, $stderr) = $node_subscriber->psql(
+	'postgres', "ALTER SUBSCRIPTION regress_sub SET (two_phase = off);");
+ok($stderr =~ /cannot alter two_phase = off when there are prepared transactions/,
+	'ALTER SUBSCRIPTION failed');
+
+# Verify the prepared transaction still exists
+$result = $node_subscriber->safe_psql('postgres',
+    "SELECT count(*) FROM pg_prepared_xacts;");
+is($result, q(1), "prepared transaction still exits");
+
+$log_offset = -s $node_subscriber->logfile;
+
+# Alter the two_phase with the force_alter option. Apart from the above, the
+# command will abort the prepared transaction and succeed. 
+$node_subscriber->safe_psql('postgres',
+    "ALTER SUBSCRIPTION regress_sub SET (two_phase = off, force_alter = true);");
+$node_subscriber->safe_psql('postgres', "ALTER SUBSCRIPTION regress_sub ENABLE;");
+
+# Verify the started worker recognized two_phase was disabled
+$node_subscriber->wait_for_log(
+	'logical replication apply worker for subscription "regress_sub" two_phase is DISABLED', $log_offset);
+
+# Verify the prepared transaction are aborted
 $result = $node_subscriber->safe_psql('postgres',
     "SELECT count(*) FROM pg_prepared_xacts;");
 is($result, q(0), "prepared transaction done by worker is aborted");
-- 
2.43.0

From 64bcb161e2386010dd7d3cd50fd7ab51e6bddb1f Mon Sep 17 00:00:00 2001
From: Ajin Cherian <ajinc@fast.au.fujitsu.com>
Date: Fri, 5 Apr 2024 06:47:18 -0400
Subject: [PATCH v9 1/4] Allow altering of two_phase option of a SUBSCRIPTION

This patch allows the user to alter the 'two_phase' option of a subscriber provided no
uncommitted prepared transactions are pending on that subscription.

Author: Cherian Ajin, Hayato Kuroda
---
 doc/src/sgml/ref/alter_subscription.sgml      | 12 ++--
 src/backend/access/transam/twophase.c         | 62 ++++++++++++++++
 src/backend/commands/subscriptioncmds.c       | 67 +++++++++++++----
 .../libpqwalreceiver/libpqwalreceiver.c       |  9 +--
 src/backend/replication/logical/launcher.c    | 22 ++++++
 src/backend/replication/logical/worker.c      | 21 +-----
 src/backend/replication/slot.c                | 18 ++++-
 src/backend/replication/walsender.c           | 18 ++++-
 src/bin/psql/tab-complete.c                   |  2 +-
 src/include/access/twophase.h                 |  5 ++
 src/include/replication/slot.h                |  3 +-
 src/include/replication/walreceiver.h         | 11 +--
 src/include/replication/worker_internal.h     |  1 +
 src/test/regress/expected/subscription.out    |  5 +-
 src/test/regress/sql/subscription.sql         |  5 +-
 src/test/subscription/t/021_twophase.pl       | 71 ++++++++++++++++++-
 16 files changed, 269 insertions(+), 63 deletions(-)

diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index a78c1c3a47..88e9a72147 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -68,8 +68,9 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
   <para>
    Commands <command>ALTER SUBSCRIPTION ... REFRESH PUBLICATION</command>,
    <command>ALTER SUBSCRIPTION ... {SET|ADD|DROP} PUBLICATION ...</command>
-   with <literal>refresh</literal> option as <literal>true</literal> and
-   <command>ALTER SUBSCRIPTION ... SET (failover = on|off)</command>
+   with <literal>refresh</literal> option as <literal>true</literal>,
+   <command>ALTER SUBSCRIPTION ... SET (failover = on|off)</command> and
+   <command>ALTER SUBSCRIPTION ... SET (two_phase = on|off)</command>
    cannot be executed inside a transaction block.
 
    These commands also cannot be executed when the subscription has
@@ -228,9 +229,12 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-disable-on-error"><literal>disable_on_error</literal></link>,
       <link linkend="sql-createsubscription-params-with-password-required"><literal>password_required</literal></link>,
       <link linkend="sql-createsubscription-params-with-run-as-owner"><literal>run_as_owner</literal></link>,
-      <link linkend="sql-createsubscription-params-with-origin"><literal>origin</literal></link>, and
-      <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>.
+      <link linkend="sql-createsubscription-params-with-origin"><literal>origin</literal></link>,
+      <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>, and
+      <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>.
       Only a superuser can set <literal>password_required = false</literal>.
+      The <literal>two_phase</literal> parameter can only be altered when the
+      subscription is disabled.
      </para>
 
      <para>
diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index 8090ac9fc1..66fa591eb5 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -2682,3 +2682,65 @@ LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 	LWLockRelease(TwoPhaseStateLock);
 	return found;
 }
+
+/*
+ * TwoPhaseTransactionGid
+ *		Form the prepared transaction GID for two_phase transactions.
+ *
+ * Return the GID in the supplied buffer.
+ */
+void
+TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid, int szgid)
+{
+	Assert(subid != InvalidRepOriginId);
+
+	if (!TransactionIdIsValid(xid))
+		ereport(ERROR,
+				(errcode(ERRCODE_PROTOCOL_VIOLATION),
+				 errmsg_internal("invalid two-phase transaction ID")));
+
+	snprintf(gid, szgid, "pg_gid_%u_%u", subid, xid);
+}
+
+/*
+ * IsTwoPhaseTransactionGidForSubid
+ *		Check whether the given GID (as formed by TwoPhaseTransactionGid) is
+ *		for the specified 'subid'.
+ */
+static bool
+IsTwoPhaseTransactionGidForSubid(Oid subid, char *gid)
+{
+	int				ret;
+	Oid				subid_written;
+	TransactionId	xid;
+
+	ret = sscanf(gid, "pg_gid_%u_%u", &subid_written, &xid);
+
+	return (ret == 2 && subid == subid_written);
+}
+
+/*
+ * LookupGXactBySubid
+ *		Check if the prepared transaction done by apply worker exists.
+ */
+bool
+LookupGXactBySubid(Oid subid)
+{
+	bool		found = false;
+
+	LWLockAcquire(TwoPhaseStateLock, LW_SHARED);
+	for (int i = 0; i < TwoPhaseState->numPrepXacts; i++)
+	{
+		GlobalTransaction gxact = TwoPhaseState->prepXacts[i];
+
+		/* Ignore not-yet-valid GIDs. */
+		if (gxact->valid &&
+			IsTwoPhaseTransactionGidForSubid(subid, gxact->gid))
+		{
+			found = true;
+			break;
+		}
+	}
+	LWLockRelease(TwoPhaseStateLock);
+	return found;
+}
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index e407428dbc..90d967eb7c 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -16,6 +16,7 @@
 
 #include "access/htup_details.h"
 #include "access/table.h"
+#include "access/twophase.h"
 #include "access/xact.h"
 #include "catalog/catalog.h"
 #include "catalog/dependency.h"
@@ -1143,7 +1144,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 			{
 				supported_opts = (SUBOPT_SLOT_NAME |
 								  SUBOPT_SYNCHRONOUS_COMMIT | SUBOPT_BINARY |
-								  SUBOPT_STREAMING | SUBOPT_DISABLE_ON_ERR |
+								  SUBOPT_STREAMING | SUBOPT_TWOPHASE_COMMIT |
+								  SUBOPT_DISABLE_ON_ERR |
 								  SUBOPT_PASSWORD_REQUIRED |
 								  SUBOPT_RUN_AS_OWNER | SUBOPT_FAILOVER |
 								  SUBOPT_ORIGIN);
@@ -1151,6 +1153,52 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 				parse_subscription_options(pstate, stmt->options,
 										   supported_opts, &opts);
 
+				if (IsSet(opts.specified_opts, SUBOPT_TWOPHASE_COMMIT))
+				{
+					/*
+					 * Do not allow changing the two_phase option if the
+					 * subscription is enabled. This is because the two_phase
+					 * option of the slot on the publisher cannot be modified
+					 * if the slot is currently acquired by the apply worker.
+					 */
+					if (form->subenabled)
+						ereport(ERROR,
+								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+								 errmsg("cannot set %s for enabled subscription",
+										"two_phase")));
+
+					/*
+					 * Stop all the subscription workers, just in case. Workers
+					 * may still survive even if the subscription is disabled.
+					 */
+					logicalrep_workers_stop(subid);
+
+					/*
+					 * two_phase cannot be disabled if there are any
+					 * uncommitted prepared transactions present.
+					 */
+					if (!opts.twophase &&
+						form->subtwophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
+						LookupGXactBySubid(subid))
+						ereport(ERROR,
+								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+								 errmsg("cannot disable two_phase when uncommitted prepared transactions present"),
+								 errhint("Resolve these transactions and try again")));
+
+					/*
+					 * The changed two_phase option of the slot can't be rolled
+					 * back.
+					 */
+					PreventInTransactionBlock(isTopLevel, "ALTER SUBSCRIPTION ... SET (two_phase)");
+
+					/* Change system catalog acoordingly */
+					values[Anum_pg_subscription_subtwophasestate - 1] =
+						CharGetDatum(opts.twophase ?
+									 LOGICALREP_TWOPHASE_STATE_PENDING :
+									 LOGICALREP_TWOPHASE_STATE_DISABLED);
+					replaces[Anum_pg_subscription_subtwophasestate - 1] = true;
+				}
+
 				if (IsSet(opts.specified_opts, SUBOPT_SLOT_NAME))
 				{
 					/*
@@ -1505,7 +1553,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 	 * doing the database operations we won't be able to rollback altered
 	 * slot.
 	 */
-	if (replaces[Anum_pg_subscription_subfailover - 1])
+	if (replaces[Anum_pg_subscription_subfailover - 1] ||
+		replaces[Anum_pg_subscription_subtwophasestate - 1])
 	{
 		bool		must_use_password;
 		char	   *err;
@@ -1525,7 +1574,7 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 
 		PG_TRY();
 		{
-			walrcv_alter_slot(wrconn, sub->slotname, opts.failover);
+			walrcv_alter_slot(wrconn, sub->slotname, opts.failover, opts.twophase);
 		}
 		PG_FINALLY();
 		{
@@ -1562,7 +1611,6 @@ DropSubscription(DropSubscriptionStmt *stmt, bool isTopLevel)
 	char	   *subname;
 	char	   *conninfo;
 	char	   *slotname;
-	List	   *subworkers;
 	ListCell   *lc;
 	char		originname[NAMEDATALEN];
 	char	   *err = NULL;
@@ -1672,16 +1720,7 @@ DropSubscription(DropSubscriptionStmt *stmt, bool isTopLevel)
 	 * New workers won't be started because we hold an exclusive lock on the
 	 * subscription till the end of the transaction.
 	 */
-	LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
-	subworkers = logicalrep_workers_find(subid, false);
-	LWLockRelease(LogicalRepWorkerLock);
-	foreach(lc, subworkers)
-	{
-		LogicalRepWorker *w = (LogicalRepWorker *) lfirst(lc);
-
-		logicalrep_worker_stop(w->subid, w->relid);
-	}
-	list_free(subworkers);
+	logicalrep_workers_stop(subid);
 
 	/*
 	 * Remove the no-longer-useful entry in the launcher's table of apply
diff --git a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
index 3c2b1bb496..998bbd517a 100644
--- a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
+++ b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
@@ -80,7 +80,7 @@ static char *libpqrcv_create_slot(WalReceiverConn *conn,
 								  CRSSnapshotAction snapshot_action,
 								  XLogRecPtr *lsn);
 static void libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-								bool failover);
+								bool failover, bool two_phase);
 static pid_t libpqrcv_get_backend_pid(WalReceiverConn *conn);
 static WalRcvExecResult *libpqrcv_exec(WalReceiverConn *conn,
 									   const char *query,
@@ -1121,15 +1121,16 @@ libpqrcv_create_slot(WalReceiverConn *conn, const char *slotname,
  */
 static void
 libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-					bool failover)
+					bool failover, bool two_phase)
 {
 	StringInfoData cmd;
 	PGresult   *res;
 
 	initStringInfo(&cmd);
-	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( FAILOVER %s )",
+	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( FAILOVER %s, TWO_PHASE %s )",
 					 quote_identifier(slotname),
-					 failover ? "true" : "false");
+					 failover ? "true" : "false",
+					 two_phase ? "true" : "false");
 
 	res = libpqrcv_PQexec(conn->streamConn, cmd.data);
 	pfree(cmd.data);
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 66070e9131..548f6e0edb 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -623,6 +623,28 @@ logicalrep_worker_stop(Oid subid, Oid relid)
 	LWLockRelease(LogicalRepWorkerLock);
 }
 
+/*
+ * Stop all the subscription workers.
+ */
+void
+logicalrep_workers_stop(Oid subid)
+{
+	List	   *subworkers;
+	ListCell   *lc;
+
+	LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
+	/* XXX clarify the reason why not only running workers are listed. */
+	subworkers = logicalrep_workers_find(subid, false);
+	LWLockRelease(LogicalRepWorkerLock);
+	foreach(lc, subworkers)
+	{
+		LogicalRepWorker *w = (LogicalRepWorker *) lfirst(lc);
+
+		logicalrep_worker_stop(w->subid, w->relid);
+	}
+	list_free(subworkers);
+}
+
 /*
  * Stop the given logical replication parallel apply worker.
  *
diff --git a/src/backend/replication/logical/worker.c b/src/backend/replication/logical/worker.c
index b5a80fe3e8..dcf656fd45 100644
--- a/src/backend/replication/logical/worker.c
+++ b/src/backend/replication/logical/worker.c
@@ -402,7 +402,6 @@ static void apply_handle_tuple_routing(ApplyExecutionData *edata,
 									   CmdType operation);
 
 /* Compute GID for two_phase transactions */
-static void TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid, int szgid);
 
 /* Functions for skipping changes */
 static void maybe_start_skipping_changes(XLogRecPtr finish_lsn);
@@ -3911,7 +3910,7 @@ maybe_reread_subscription(void)
 	/* !slotname should never happen when enabled is true. */
 	Assert(newsub->slotname);
 
-	/* two-phase should not be altered */
+	/* two-phase cannot be altered while the worker exists */
 	Assert(newsub->twophasestate == MySubscription->twophasestate);
 
 	/*
@@ -4396,24 +4395,6 @@ cleanup_subxact_info()
 	subxact_data.nsubxacts_max = 0;
 }
 
-/*
- * Form the prepared transaction GID for two_phase transactions.
- *
- * Return the GID in the supplied buffer.
- */
-static void
-TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid, int szgid)
-{
-	Assert(subid != InvalidRepOriginId);
-
-	if (!TransactionIdIsValid(xid))
-		ereport(ERROR,
-				(errcode(ERRCODE_PROTOCOL_VIOLATION),
-				 errmsg_internal("invalid two-phase transaction ID")));
-
-	snprintf(gid, szgid, "pg_gid_%u_%u", subid, xid);
-}
-
 /*
  * Common function to run the apply loop with error handling. Disable the
  * subscription, if necessary.
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index aa4ea387da..d0c8d5a4df 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -804,8 +804,10 @@ ReplicationSlotDrop(const char *name, bool nowait)
  * Change the definition of the slot identified by the specified name.
  */
 void
-ReplicationSlotAlter(const char *name, bool failover)
+ReplicationSlotAlter(const char *name, bool failover, bool two_phase)
 {
+	bool		update_slot = false;
+
 	Assert(MyReplicationSlot == NULL);
 
 	ReplicationSlotAcquire(name, false);
@@ -854,6 +856,20 @@ ReplicationSlotAlter(const char *name, bool failover)
 		MyReplicationSlot->data.failover = failover;
 		SpinLockRelease(&MyReplicationSlot->mutex);
 
+		update_slot = true;
+	}
+
+	if (MyReplicationSlot->data.two_phase != two_phase)
+	{
+		SpinLockAcquire(&MyReplicationSlot->mutex);
+		MyReplicationSlot->data.two_phase = two_phase;
+		SpinLockRelease(&MyReplicationSlot->mutex);
+
+		update_slot = true;
+	}
+
+	if (update_slot)
+	{
 		ReplicationSlotMarkDirty();
 		ReplicationSlotSave();
 	}
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index c623b07cf0..2e6ca35049 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1411,9 +1411,11 @@ DropReplicationSlot(DropReplicationSlotCmd *cmd)
  * Process extra options given to ALTER_REPLICATION_SLOT.
  */
 static void
-ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd, bool *failover)
+ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd,
+						  bool *failover, bool *two_phase)
 {
 	bool		failover_given = false;
+	bool		two_phase_given = false;
 
 	/* Parse options */
 	foreach_ptr(DefElem, defel, cmd->options)
@@ -1427,6 +1429,15 @@ ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd, bool *failover)
 			failover_given = true;
 			*failover = defGetBoolean(defel);
 		}
+		else if (strcmp(defel->defname, "two_phase") == 0)
+		{
+			if (two_phase_given)
+				ereport(ERROR,
+						(errcode(ERRCODE_SYNTAX_ERROR),
+						 errmsg("conflicting or redundant options")));
+			two_phase_given = true;
+			*two_phase = defGetBoolean(defel);
+		}
 		else
 			elog(ERROR, "unrecognized option: %s", defel->defname);
 	}
@@ -1439,9 +1450,10 @@ static void
 AlterReplicationSlot(AlterReplicationSlotCmd *cmd)
 {
 	bool		failover = false;
+	bool		two_phase = false;
 
-	ParseAlterReplSlotOptions(cmd, &failover);
-	ReplicationSlotAlter(cmd->slotname, failover);
+	ParseAlterReplSlotOptions(cmd, &failover, &two_phase);
+	ReplicationSlotAlter(cmd->slotname, failover, two_phase);
 }
 
 /*
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
index d453e224d9..891face1b6 100644
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -1948,7 +1948,7 @@ psql_completion(const char *text, int start, int end)
 	else if (HeadMatches("ALTER", "SUBSCRIPTION", MatchAny) && TailMatches("SET", "("))
 		COMPLETE_WITH("binary", "disable_on_error", "failover", "origin",
 					  "password_required", "run_as_owner", "slot_name",
-					  "streaming", "synchronous_commit");
+					  "streaming", "synchronous_commit", "two_phase");
 	/* ALTER SUBSCRIPTION <name> SKIP ( */
 	else if (HeadMatches("ALTER", "SUBSCRIPTION", MatchAny) && TailMatches("SKIP", "("))
 		COMPLETE_WITH("lsn");
diff --git a/src/include/access/twophase.h b/src/include/access/twophase.h
index 56248c0006..d37e06fdee 100644
--- a/src/include/access/twophase.h
+++ b/src/include/access/twophase.h
@@ -62,4 +62,9 @@ extern void PrepareRedoRemove(TransactionId xid, bool giveWarning);
 extern void restoreTwoPhaseData(void);
 extern bool LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 						TimestampTz origin_prepare_timestamp);
+
+extern void TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid,
+								   int szgid);
+extern bool LookupGXactBySubid(Oid subid);
+
 #endif							/* TWOPHASE_H */
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 1bc80960ef..014e216cf5 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -243,7 +243,8 @@ extern void ReplicationSlotCreate(const char *name, bool db_specific,
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
 extern void ReplicationSlotDropAcquired(void);
-extern void ReplicationSlotAlter(const char *name, bool failover);
+extern void ReplicationSlotAlter(const char *name, bool failover,
+								 bool two_phase);
 
 extern void ReplicationSlotAcquire(const char *name, bool nowait);
 extern void ReplicationSlotRelease(void);
diff --git a/src/include/replication/walreceiver.h b/src/include/replication/walreceiver.h
index 12f71fa99b..31fa1257ec 100644
--- a/src/include/replication/walreceiver.h
+++ b/src/include/replication/walreceiver.h
@@ -372,12 +372,13 @@ typedef char *(*walrcv_create_slot_fn) (WalReceiverConn *conn,
 /*
  * walrcv_alter_slot_fn
  *
- * Change the definition of a replication slot. Currently, it only supports
- * changing the failover property of the slot.
+ * Change the definition of a replication slot. Currently, it supports
+ * changing the failover and the two_phase property of the slot.
  */
 typedef void (*walrcv_alter_slot_fn) (WalReceiverConn *conn,
 									  const char *slotname,
-									  bool failover);
+									  bool failover,
+									  bool two_phase);
 
 /*
  * walrcv_get_backend_pid_fn
@@ -455,8 +456,8 @@ extern PGDLLIMPORT WalReceiverFunctionsType *WalReceiverFunctions;
 	WalReceiverFunctions->walrcv_send(conn, buffer, nbytes)
 #define walrcv_create_slot(conn, slotname, temporary, two_phase, failover, snapshot_action, lsn) \
 	WalReceiverFunctions->walrcv_create_slot(conn, slotname, temporary, two_phase, failover, snapshot_action, lsn)
-#define walrcv_alter_slot(conn, slotname, failover) \
-	WalReceiverFunctions->walrcv_alter_slot(conn, slotname, failover)
+#define walrcv_alter_slot(conn, slotname, failover, two_phase) \
+	WalReceiverFunctions->walrcv_alter_slot(conn, slotname, failover, two_phase)
 #define walrcv_get_backend_pid(conn) \
 	WalReceiverFunctions->walrcv_get_backend_pid(conn)
 #define walrcv_exec(conn, exec, nRetTypes, retTypes) \
diff --git a/src/include/replication/worker_internal.h b/src/include/replication/worker_internal.h
index 515aefd519..d5428263c1 100644
--- a/src/include/replication/worker_internal.h
+++ b/src/include/replication/worker_internal.h
@@ -246,6 +246,7 @@ extern bool logicalrep_worker_launch(LogicalRepWorkerType wtype,
 									 Oid userid, Oid relid,
 									 dsm_handle subworker_dsm);
 extern void logicalrep_worker_stop(Oid subid, Oid relid);
+extern void logicalrep_workers_stop(Oid subid);
 extern void logicalrep_pa_worker_stop(ParallelApplyWorkerInfo *winfo);
 extern void logicalrep_worker_wakeup(Oid subid, Oid relid);
 extern void logicalrep_worker_wakeup_ptr(LogicalRepWorker *worker);
diff --git a/src/test/regress/expected/subscription.out b/src/test/regress/expected/subscription.out
index 0f2a25cdc1..51fa4b9690 100644
--- a/src/test/regress/expected/subscription.out
+++ b/src/test/regress/expected/subscription.out
@@ -377,10 +377,7 @@ HINT:  To initiate replication, you must manually create the replication slot, e
  regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | p                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
---fail - alter of two_phase option not supported.
-ALTER SUBSCRIPTION regress_testsub SET (two_phase = false);
-ERROR:  unrecognized subscription parameter: "two_phase"
--- but can alter streaming when two_phase enabled
+-- We can alter streaming when two_phase enabled
 ALTER SUBSCRIPTION regress_testsub SET (streaming = true);
 \dRs+
                                                                                                                 List of subscriptions
diff --git a/src/test/regress/sql/subscription.sql b/src/test/regress/sql/subscription.sql
index 3e5ba4cb8c..a3886d79ca 100644
--- a/src/test/regress/sql/subscription.sql
+++ b/src/test/regress/sql/subscription.sql
@@ -256,10 +256,7 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUBLICATION testpub WITH (connect = false, two_phase = true);
 
 \dRs+
---fail - alter of two_phase option not supported.
-ALTER SUBSCRIPTION regress_testsub SET (two_phase = false);
-
--- but can alter streaming when two_phase enabled
+-- We can alter streaming when two_phase enabled
 ALTER SUBSCRIPTION regress_testsub SET (streaming = true);
 
 \dRs+
diff --git a/src/test/subscription/t/021_twophase.pl b/src/test/subscription/t/021_twophase.pl
index 9437cd4c3b..72df258000 100644
--- a/src/test/subscription/t/021_twophase.pl
+++ b/src/test/subscription/t/021_twophase.pl
@@ -367,6 +367,75 @@ $result =
   $node_subscriber->safe_psql('postgres', "SELECT count(*) FROM tab_copy;");
 is($result, qq(2), 'replicated data in subscriber table');
 
+# Clean up
+$node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub");
+
+###############################
+# Disable the subscription and alter it to two_phase = false,
+# then verify that the altered subscription reflects the two_phase option.
+###############################
+
+# Alter subscription two_phase to false
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy DISABLE");
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = false)");
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy ENABLE");
+
+# Wait for subscription startup
+$node_subscriber->wait_for_subscription_sync($node_publisher, $appname_copy);
+
+# Make sure that the two-phase is disabled on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+       "SELECT subtwophasestate FROM pg_subscription WHERE subname = 'tap_sub_copy';"
+);
+is($result, qq(d), 'two-phase should be disabled');
+
+# Now do a prepare on the publisher and make sure that it is not replicated.
+$node_publisher->safe_psql(
+       'postgres', qq{
+    BEGIN;
+    INSERT INTO tab_copy VALUES (100);
+    PREPARE TRANSACTION 'newgid';
+	});
+
+# Wait for the subscriber to catchup
+$node_publisher->wait_for_catchup($appname_copy);
+
+# Make sure there are no prepared transactions on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT count(*) FROM pg_prepared_xacts;");
+is($result, qq(0), 'should be no prepared transactions on subscriber');
+
+# Now commit the insert and verify that it IS replicated
+$node_publisher->safe_psql('postgres', "COMMIT PREPARED 'newgid';");
+
+# Wait for the subscriber to catchup
+$node_publisher->wait_for_catchup($appname_copy);
+
+# Make sure that the committed transaction is replicated.
+$result =
+	$node_subscriber->safe_psql('postgres', "SELECT count(*) FROM tab_copy;");
+is($result, qq(3), 'replicated data in subscriber table');
+
+# Alter subscription two_phase to true
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy DISABLE");
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = true)");
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy ENABLE");
+
+# Wait for subscription startup
+$node_subscriber->wait_for_subscription_sync($node_publisher, $appname_copy);
+
+# Make sure that the two-phase is enabled on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT subtwophasestate FROM pg_subscription WHERE subname = 'tap_sub_copy';"
+);
+is($result, qq(e), 'two-phase should be enabled');
+
 $node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub_copy;");
 $node_publisher->safe_psql('postgres', "DROP PUBLICATION tap_pub_copy;");
 
@@ -374,8 +443,6 @@ $node_publisher->safe_psql('postgres', "DROP PUBLICATION tap_pub_copy;");
 # check all the cleanup
 ###############################
 
-$node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub");
-
 $result = $node_subscriber->safe_psql('postgres',
 	"SELECT count(*) FROM pg_subscription");
 is($result, qq(0), 'check subscription was dropped on subscriber');
-- 
2.43.0

From 73d327729fcece36100bdc9e9b91d2b933c90c39 Mon Sep 17 00:00:00 2001
From: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Date: Wed, 17 Apr 2024 06:18:23 +0000
Subject: [PATCH v9 2/4] Alter slot option two_phase only when altering "on" to
 "off"

Since the two_phase option is controlled by both the publisher (as a slot option)
and the subscriber (as a subscription option), the slot option must also be
modified.

Regarding the off->on case, the logical replication already has a mechanism for
it, so there is no need to do anything special for the on->off case; however,
we must connect to the publisher and expressly change the parameter. The
operation cannot be rolled back, and altering the parameter from "on" to "off"
within a transaction is prohibited.

In the opposite case, there is no need to prevent this because the logical
replication worker already had the mechanism to alter the slot option at a
convenient time.
---
 doc/src/sgml/ref/alter_subscription.sgml      |  2 +-
 src/backend/commands/subscriptioncmds.c       | 36 +++++--
 .../libpqwalreceiver/libpqwalreceiver.c       | 23 +++--
 src/include/replication/walreceiver.h         |  5 +-
 src/test/subscription/meson.build             |  1 +
 src/test/subscription/t/099_twophase_added.pl | 96 +++++++++++++++++++
 6 files changed, 147 insertions(+), 16 deletions(-)
 create mode 100644 src/test/subscription/t/099_twophase_added.pl

diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index 88e9a72147..0c2894a94e 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -70,7 +70,7 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
    <command>ALTER SUBSCRIPTION ... {SET|ADD|DROP} PUBLICATION ...</command>
    with <literal>refresh</literal> option as <literal>true</literal>,
    <command>ALTER SUBSCRIPTION ... SET (failover = on|off)</command> and
-   <command>ALTER SUBSCRIPTION ... SET (two_phase = on|off)</command>
+   <command>ALTER SUBSCRIPTION ... SET (two_phase = off)</command>
    cannot be executed inside a transaction block.
 
    These commands also cannot be executed when the subscription has
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index 90d967eb7c..4021defcea 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -1097,6 +1097,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 	Form_pg_subscription form;
 	bits32		supported_opts;
 	SubOpts		opts = {0};
+	bool		update_failover;
+	bool		update_two_phase;
 
 	rel = table_open(SubscriptionRelationId, RowExclusiveLock);
 
@@ -1186,10 +1188,17 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 								 errhint("Resolve these transactions and try again")));
 
 					/*
-					 * The changed two_phase option of the slot can't be rolled
-					 * back.
+					 * Since altering the two_phase option of subscriptions
+					 * also leads to changing the slot option, this command
+					 * cannot be rolled back. So prevent this if we are in a
+					 * transaction block. In the opposite case, there is no
+					 * need to prevent this because the logical replication
+					 * worker already had the mechanism to alter the slot
+					 * option at a convenient time.
 					 */
-					PreventInTransactionBlock(isTopLevel, "ALTER SUBSCRIPTION ... SET (two_phase)");
+					if (!opts.twophase)
+						PreventInTransactionBlock(isTopLevel,
+												  "ALTER SUBSCRIPTION ... SET (two_phase = off)");
 
 					/* Change system catalog acoordingly */
 					values[Anum_pg_subscription_subtwophasestate - 1] =
@@ -1547,14 +1556,25 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 	}
 
 	/*
-	 * Try to acquire the connection necessary for altering slot.
+	 * Check the need to alter the replication slot. Failover and two_phase
+	 * options are controlled by both the publisher (as a slot option) and the
+	 * subscriber (as a subscription option). The slot option must be altered
+	 * only when changing "on" to "off". Because in opposite case, the logical
+	 * replication worker already has the mechanism to do so at a convenient
+	 * time.
+	 */
+	update_failover = replaces[Anum_pg_subscription_subfailover - 1];
+	update_two_phase = (replaces[Anum_pg_subscription_subtwophasestate - 1] &&
+						!opts.twophase);
+
+	/*
+	 * Try to acquire the connection necessary for altering slot, if needed.
 	 *
 	 * This has to be at the end because otherwise if there is an error while
 	 * doing the database operations we won't be able to rollback altered
 	 * slot.
 	 */
-	if (replaces[Anum_pg_subscription_subfailover - 1] ||
-		replaces[Anum_pg_subscription_subtwophasestate - 1])
+	if (update_failover || update_two_phase)
 	{
 		bool		must_use_password;
 		char	   *err;
@@ -1574,7 +1594,9 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 
 		PG_TRY();
 		{
-			walrcv_alter_slot(wrconn, sub->slotname, opts.failover, opts.twophase);
+			walrcv_alter_slot(wrconn, sub->slotname,
+							  update_failover ? &opts.failover : NULL,
+							  update_two_phase ? &opts.twophase : NULL);
 		}
 		PG_FINALLY();
 		{
diff --git a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
index 998bbd517a..ff013aa987 100644
--- a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
+++ b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
@@ -80,7 +80,7 @@ static char *libpqrcv_create_slot(WalReceiverConn *conn,
 								  CRSSnapshotAction snapshot_action,
 								  XLogRecPtr *lsn);
 static void libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-								bool failover, bool two_phase);
+								const bool *failover, const bool *two_phase);
 static pid_t libpqrcv_get_backend_pid(WalReceiverConn *conn);
 static WalRcvExecResult *libpqrcv_exec(WalReceiverConn *conn,
 									   const char *query,
@@ -1121,16 +1121,27 @@ libpqrcv_create_slot(WalReceiverConn *conn, const char *slotname,
  */
 static void
 libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-					bool failover, bool two_phase)
+					const bool *failover, const bool *two_phase)
 {
 	StringInfoData cmd;
 	PGresult   *res;
 
 	initStringInfo(&cmd);
-	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( FAILOVER %s, TWO_PHASE %s )",
-					 quote_identifier(slotname),
-					 failover ? "true" : "false",
-					 two_phase ? "true" : "false");
+	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( ",
+					 quote_identifier(slotname));
+
+	if (failover)
+		appendStringInfo(&cmd, "FAILOVER %s",
+						 *failover ? "true" : "false");
+
+	if (failover && two_phase)
+		appendStringInfo(&cmd, ", ");
+
+	if (two_phase)
+		appendStringInfo(&cmd, "TWO_PHASE %s",
+						 *two_phase ? "true" : "false");
+
+	appendStringInfoString(&cmd, " );");
 
 	res = libpqrcv_PQexec(conn->streamConn, cmd.data);
 	pfree(cmd.data);
diff --git a/src/include/replication/walreceiver.h b/src/include/replication/walreceiver.h
index 31fa1257ec..7ffa5a58b3 100644
--- a/src/include/replication/walreceiver.h
+++ b/src/include/replication/walreceiver.h
@@ -377,8 +377,9 @@ typedef char *(*walrcv_create_slot_fn) (WalReceiverConn *conn,
  */
 typedef void (*walrcv_alter_slot_fn) (WalReceiverConn *conn,
 									  const char *slotname,
-									  bool failover,
-									  bool two_phase);
+									  const bool *failover,
+									  const bool *two_phase);
+
 
 /*
  * walrcv_get_backend_pid_fn
diff --git a/src/test/subscription/meson.build b/src/test/subscription/meson.build
index c591cd7d61..b4bd522c3d 100644
--- a/src/test/subscription/meson.build
+++ b/src/test/subscription/meson.build
@@ -40,6 +40,7 @@ tests += {
       't/031_column_list.pl',
       't/032_subscribe_use_index.pl',
       't/033_run_as_table_owner.pl',
+      't/099_twophase_added.pl',
       't/100_bugs.pl',
     ],
   },
diff --git a/src/test/subscription/t/099_twophase_added.pl b/src/test/subscription/t/099_twophase_added.pl
new file mode 100644
index 0000000000..db6cba1699
--- /dev/null
+++ b/src/test/subscription/t/099_twophase_added.pl
@@ -0,0 +1,96 @@
+# Copyright (c) 2024, PostgreSQL Global Development Group
+
+# Additional tests for altering two_phase option
+use strict;
+use warnings FATAL => 'all';
+use PostgreSQL::Test::Cluster;
+use PostgreSQL::Test::Utils;
+use Test::More;
+
+# Initialize publisher node
+my $node_publisher = PostgreSQL::Test::Cluster->new('publisher');
+$node_publisher->init(allows_streaming => 'logical');
+$node_publisher->append_conf('postgresql.conf',
+	qq(max_prepared_transactions = 10));
+$node_publisher->start;
+
+# Create subscriber node
+my $node_subscriber = PostgreSQL::Test::Cluster->new('subscriber');
+$node_subscriber->init;
+$node_subscriber->append_conf('postgresql.conf',
+	qq(max_prepared_transactions = 10
+	log_min_messages = debug1));
+$node_subscriber->start;
+
+# Define tables on both nodes
+$node_publisher->safe_psql('postgres',
+    "CREATE TABLE tab_full (a int PRIMARY KEY);");
+$node_subscriber->safe_psql('postgres',
+	"CREATE TABLE tab_full (a int PRIMARY KEY)");
+
+# Setup logical replication, with two_phase = "off"
+my $publisher_connstr = $node_publisher->connstr . ' dbname=postgres';
+$node_publisher->safe_psql('postgres',
+	"CREATE PUBLICATION pub FOR ALL TABLES");
+
+my $log_offset = -s $node_subscriber->logfile;
+
+$node_subscriber->safe_psql(
+	'postgres', "
+	CREATE SUBSCRIPTION regress_sub
+	CONNECTION '$publisher_connstr' PUBLICATION pub
+	WITH (two_phase = off, copy_data = off, failover = off)");
+
+# Verify the started worker recognized two_phase was disabled
+$node_subscriber->wait_for_log(
+	'logical replication apply worker for subscription "regress_sub" two_phase is DISABLED', $log_offset);
+
+#####################
+# Check the case that prepared transactions exist on the publisher node.
+#
+# Since the two_phase is "off", then normally, this PREPARE will do nothing
+# until the COMMIT PREPARED, but in this test, we toggle the two_phase to "on"
+# again before the COMMIT PREPARED happens.
+
+# Prepare a transaction to insert some tuples into the table
+$node_publisher->safe_psql(
+	'postgres', "
+	BEGIN;
+	INSERT INTO tab_full VALUES (generate_series(1, 5));
+	PREPARE TRANSACTION 'test_prepared_tab_full';");
+
+$node_publisher->wait_for_catchup('regress_sub');
+
+# Verify the prepared transaction is not yet replicated to the subscriber
+# because two_phase is set to "off".
+my $result = $node_subscriber->safe_psql('postgres',
+    "SELECT count(*) FROM pg_prepared_xacts;");
+is($result, q(0), "transaction is not prepared on subscriber");
+
+$log_offset = -s $node_subscriber->logfile;
+
+# Toggle the two_phase to "on" *before* the COMMIT PREPARED. Since we are the
+# special path for the case where both two_phase and failover are altered, it
+# is also set to "on".
+$node_subscriber->safe_psql(
+    'postgres', "
+    ALTER SUBSCRIPTION regress_sub DISABLE;
+    ALTER SUBSCRIPTION regress_sub SET (two_phase = on, failover = on);
+    ALTER SUBSCRIPTION regress_sub ENABLE;");
+
+# Verify the started worker recognized two_phase was enabled
+$node_subscriber->wait_for_log(
+	'logical replication apply worker for subscription "regress_sub" two_phase is ENABLED', $log_offset);
+
+# And do COMMIT PREPARED the prepared transaction
+$node_publisher->safe_psql('postgres',
+    "COMMIT PREPARED 'test_prepared_tab_full';");
+$node_publisher->wait_for_catchup('regress_sub');
+
+# Verify inserted tuples are replicated
+$result = $node_subscriber->safe_psql('postgres',
+    "SELECT count(*) FROM tab_full;");
+is($result, q(5),
+   "prepared transactions done before altering can be replicated");
+
+done_testing();
-- 
2.43.0

From 1f4ac6ef248dda223ea451f74c13d2db73d72f75 Mon Sep 17 00:00:00 2001
From: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Date: Mon, 8 Apr 2024 12:39:12 +0000
Subject: [PATCH v9 3/4] Abort prepared transactions while altering two_phase
 to off

If we alter the two_phase parameter from "on" to "off" and there are prepared
transactions on the subscriber, they won't be resolved. To avoid this issue, we
allow the backend to abort all prepared transactions while altering the
subscription.
---
 doc/src/sgml/ref/alter_subscription.sgml      | 11 ++++-
 src/backend/access/transam/twophase.c         | 17 +++----
 src/backend/commands/subscriptioncmds.c       | 48 ++++++++++++-------
 src/include/access/twophase.h                 |  3 +-
 src/test/subscription/t/099_twophase_added.pl | 45 +++++++++++++++++
 5 files changed, 93 insertions(+), 31 deletions(-)

diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index 0c2894a94e..74728a503d 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -233,8 +233,6 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>, and
       <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>.
       Only a superuser can set <literal>password_required = false</literal>.
-      The <literal>two_phase</literal> parameter can only be altered when the
-      subscription is disabled.
      </para>
 
      <para>
@@ -256,6 +254,15 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>
       option is enabled.
      </para>
+
+     <para>
+      The <literal>two_phase</literal> parameter can only be altered when the
+      subscription is disabled. When altering the parameter from <literal>on</literal>
+      to <literal>off</literal>, the backend process checks for any incomplete
+      prepared transactions done by the logical replication worker (from when
+      <literal>two_phase</literal> parameter was still <literal>on</literal>)
+      and, if any are found, those are aborted.
+     </para>
     </listitem>
    </varlistentry>
 
diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index 66fa591eb5..f384bd8c0a 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -2720,13 +2720,13 @@ IsTwoPhaseTransactionGidForSubid(Oid subid, char *gid)
 }
 
 /*
- * LookupGXactBySubid
- *		Check if the prepared transaction done by apply worker exists.
+ * GetGidListBySubid
+ *      Get a list of GIDs which is PREPARE'd by the given subscription.
  */
-bool
-LookupGXactBySubid(Oid subid)
+List *
+GetGidListBySubid(Oid subid)
 {
-	bool		found = false;
+	List *list = NIL;
 
 	LWLockAcquire(TwoPhaseStateLock, LW_SHARED);
 	for (int i = 0; i < TwoPhaseState->numPrepXacts; i++)
@@ -2736,11 +2736,8 @@ LookupGXactBySubid(Oid subid)
 		/* Ignore not-yet-valid GIDs. */
 		if (gxact->valid &&
 			IsTwoPhaseTransactionGidForSubid(subid, gxact->gid))
-		{
-			found = true;
-			break;
-		}
+			list = lappend(list, pstrdup(gxact->gid));
 	}
 	LWLockRelease(TwoPhaseStateLock);
-	return found;
+	return list;
 }
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index 4021defcea..97bd11bc4a 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -1176,30 +1176,42 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 					logicalrep_workers_stop(subid);
 
 					/*
-					 * two_phase cannot be disabled if there are any
-					 * uncommitted prepared transactions present.
+					 * If two_phase was enabled, there is a possibility that
+					 * transactions have already been PREPARE'd. They must be
+					 * checked and rolled back.
 					 */
-					if (!opts.twophase &&
-						form->subtwophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
-						LookupGXactBySubid(subid))
-						ereport(ERROR,
-								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-								 errmsg("cannot disable two_phase when uncommitted prepared transactions present"),
-								 errhint("Resolve these transactions and try again")));
 
-					/*
-					 * Since altering the two_phase option of subscriptions
-					 * also leads to changing the slot option, this command
-					 * cannot be rolled back. So prevent this if we are in a
-					 * transaction block. In the opposite case, there is no
-					 * need to prevent this because the logical replication
-					 * worker already had the mechanism to alter the slot
-					 * option at a convenient time.
-					 */
 					if (!opts.twophase)
+					{
+						List *prepared_xacts;
+
+						/*
+						 * Since altering the two_phase option of subscriptions
+						 * also leads to changing the slot option, this command
+						 * cannot be rolled back. So prevent this if we are in a
+						 * transaction block. In the opposite case, there is no
+						 * need to prevent this because the logical replication
+						 * worker already had the mechanism to alter the slot
+						 * option at a convenient time.
+						 */
 						PreventInTransactionBlock(isTopLevel,
 												  "ALTER SUBSCRIPTION ... SET (two_phase = off)");
 
+						/*
+						 * To prevent prepared transactions from being
+						 * isolated, they must manually be aborted.
+						 */
+						if (sub->twophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
+							(prepared_xacts = GetGidListBySubid(subid)) != NIL)
+						{
+							/* Abort all listed transactions */
+							foreach_ptr(char, gid, prepared_xacts)
+								FinishPreparedTransaction(gid, false);
+
+							list_free_deep(prepared_xacts);
+						}
+					}
+
 					/* Change system catalog acoordingly */
 					values[Anum_pg_subscription_subtwophasestate - 1] =
 						CharGetDatum(opts.twophase ?
diff --git a/src/include/access/twophase.h b/src/include/access/twophase.h
index d37e06fdee..f7a5cf0c12 100644
--- a/src/include/access/twophase.h
+++ b/src/include/access/twophase.h
@@ -18,6 +18,7 @@
 #include "access/xlogdefs.h"
 #include "datatype/timestamp.h"
 #include "storage/lock.h"
+#include "nodes/pg_list.h"
 
 /*
  * GlobalTransactionData is defined in twophase.c; other places have no
@@ -65,6 +66,6 @@ extern bool LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 
 extern void TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid,
 								   int szgid);
-extern bool LookupGXactBySubid(Oid subid);
+extern List *GetGidListBySubid(Oid subid);
 
 #endif							/* TWOPHASE_H */
diff --git a/src/test/subscription/t/099_twophase_added.pl b/src/test/subscription/t/099_twophase_added.pl
index db6cba1699..9cc1ca9167 100644
--- a/src/test/subscription/t/099_twophase_added.pl
+++ b/src/test/subscription/t/099_twophase_added.pl
@@ -93,4 +93,49 @@ $result = $node_subscriber->safe_psql('postgres',
 is($result, q(5),
    "prepared transactions done before altering can be replicated");
 
+#####################
+# Check the case that prepared transactions exist on the subscriber node
+#
+# If the two_phase is altering from "on" to "off" and there are prepared
+# transactions on the subscriber, they must be aborted. This test checks it.
+
+# Prepare a transaction to insert some tuples into the table
+$node_publisher->safe_psql(
+	'postgres', "
+	BEGIN;
+	INSERT INTO tab_full VALUES (generate_series(6, 10));
+	PREPARE TRANSACTION 'test_prepared_tab_full';");
+
+$node_publisher->wait_for_catchup('regress_sub');
+
+# Verify the prepared transaction has been replicated to the subscriber because
+# two_phase is set to "on".
+$result = $node_subscriber->safe_psql('postgres',
+    "SELECT count(*) FROM pg_prepared_xacts;");
+is($result, q(1), "transaction has been prepared on subscriber");
+
+# Toggle the two_phase to "off" before the COMMIT PREPARED
+$node_subscriber->safe_psql(
+    'postgres', "
+    ALTER SUBSCRIPTION regress_sub DISABLE;
+    ALTER SUBSCRIPTION regress_sub SET (two_phase = off);
+    ALTER SUBSCRIPTION regress_sub ENABLE;");
+
+# Verify any prepared transactions are aborted because two_phase is changed to
+# "off".
+$result = $node_subscriber->safe_psql('postgres',
+    "SELECT count(*) FROM pg_prepared_xacts;");
+is($result, q(0), "prepared transaction done by worker is aborted");
+
+# Do COMMIT PREPARED the prepared transaction
+$node_publisher->safe_psql( 'postgres',
+    "COMMIT PREPARED 'test_prepared_tab_full';");
+$node_publisher->wait_for_catchup('regress_sub');
+
+# Verify inserted tuples are replicated
+$result = $node_subscriber->safe_psql('postgres',
+    "SELECT count(10) FROM tab_full;");
+is($result, q(10),
+   "prepared transactions on publisher can be replicated");
+
 done_testing();
-- 
2.43.0

From 1dd9ac0ee519b63881bdd12aba1a8782662b1188 Mon Sep 17 00:00:00 2001
From: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Date: Fri, 19 Apr 2024 11:03:19 +0000
Subject: [PATCH v9 4/4] Add force_alter option for ALTER SUBSCRIPTION ... SET
 command

Previously, all prepared transactions on the standby were rolled back when
toggling two_phase from "on" to "off". However, this operation may not be
expected by users. To ensure users understand what happens, we added the
"force_alter" parameter. When two_phase is toggling to "off", and there are
prepared transactions, they will be aborted only when "force_alter" is set to
true. Otherwise, an ERROR occurs.
---
 doc/src/sgml/catalogs.sgml                    |  10 ++
 doc/src/sgml/ref/alter_subscription.sgml      |  16 +-
 doc/src/sgml/ref/create_subscription.sgml     |  18 +++
 src/backend/catalog/pg_subscription.c         |   1 +
 src/backend/catalog/system_views.sql          |   2 +-
 src/backend/commands/subscriptioncmds.c       |  45 +++++-
 src/bin/pg_dump/pg_dump.c                     |  15 ++
 src/bin/pg_dump/pg_dump.h                     |   1 +
 src/bin/psql/describe.c                       |   7 +-
 src/include/catalog/pg_subscription.h         |   6 +
 src/test/regress/expected/subscription.out    | 152 +++++++++---------
 src/test/subscription/t/099_twophase_added.pl |  43 +++--
 12 files changed, 216 insertions(+), 100 deletions(-)

diff --git a/doc/src/sgml/catalogs.sgml b/doc/src/sgml/catalogs.sgml
index b530c030f0..6a7b2faa66 100644
--- a/doc/src/sgml/catalogs.sgml
+++ b/doc/src/sgml/catalogs.sgml
@@ -8046,6 +8046,16 @@ SCRAM-SHA-256$<replaceable>&lt;iteration count&gt;</replaceable>:<replaceable>&l
       </para></entry>
      </row>
 
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>subforcealter</structfield> <type>bool</type>
+      </para>
+      <para>
+       If true, the subscription can be altered <literal>two_phase</literal>
+       option, even if there are prepared transactions
+      </para></entry>
+     </row>
+
      <row>
       <entry role="catalog_table_entry"><para role="column_definition">
        <structfield>subconninfo</structfield> <type>text</type>
diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index 74728a503d..e7c363a1c9 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -230,9 +230,12 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-password-required"><literal>password_required</literal></link>,
       <link linkend="sql-createsubscription-params-with-run-as-owner"><literal>run_as_owner</literal></link>,
       <link linkend="sql-createsubscription-params-with-origin"><literal>origin</literal></link>,
-      <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>, and
-      <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>.
+      <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>,
+      <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>, and
+      <link linkend="sql-createsubscription-params-with-force-alter"><literal>force_alter</literal></link>
       Only a superuser can set <literal>password_required = false</literal>.
+      The <literal>two_phase</literal> parameter can only be altered when the
+      subscription is disabled.
      </para>
 
      <para>
@@ -254,15 +257,6 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>
       option is enabled.
      </para>
-
-     <para>
-      The <literal>two_phase</literal> parameter can only be altered when the
-      subscription is disabled. When altering the parameter from <literal>on</literal>
-      to <literal>off</literal>, the backend process checks for any incomplete
-      prepared transactions done by the logical replication worker (from when
-      <literal>two_phase</literal> parameter was still <literal>on</literal>)
-      and, if any are found, those are aborted.
-     </para>
     </listitem>
    </varlistentry>
 
diff --git a/doc/src/sgml/ref/create_subscription.sgml b/doc/src/sgml/ref/create_subscription.sgml
index 740b7d9421..a4f30b4453 100644
--- a/doc/src/sgml/ref/create_subscription.sgml
+++ b/doc/src/sgml/ref/create_subscription.sgml
@@ -428,6 +428,24 @@ CREATE SUBSCRIPTION <replaceable class="parameter">subscription_name</replaceabl
          </para>
         </listitem>
        </varlistentry>
+
+       <varlistentry id="sql-createsubscription-params-with-force-alter">
+        <term><literal>force_alter</literal> (<type>boolean</type>)</term>
+        <listitem>
+         <para>
+          Specifies whether the subscription can be altered
+          <literal>two_phase</literal> option, even if there are prepared
+          transactions. If specified, the backend process checks for any
+          incomplete prepared transactions done by the logical replication
+          worker (from when <literal>two_phase</literal> parameter was still
+          <literal>on</literal>), if any are found, those are aborted.
+          Otherwise, Altering the parameter from <literal>on</literal> to
+          <literal>off</literal> will give an error when there are prepared
+          transactions done by the logical replication worker.
+          The default is <literal>false</literal>.
+         </para>
+        </listitem>
+       </varlistentry>
       </variablelist></para>
 
     </listitem>
diff --git a/src/backend/catalog/pg_subscription.c b/src/backend/catalog/pg_subscription.c
index 9efc9159f2..b568fe3470 100644
--- a/src/backend/catalog/pg_subscription.c
+++ b/src/backend/catalog/pg_subscription.c
@@ -72,6 +72,7 @@ GetSubscription(Oid subid, bool missing_ok)
 	sub->passwordrequired = subform->subpasswordrequired;
 	sub->runasowner = subform->subrunasowner;
 	sub->failover = subform->subfailover;
+	sub->forcealter = subform->subforcealter;
 
 	/* Get conninfo */
 	datum = SysCacheGetAttrNotNull(SUBSCRIPTIONOID,
diff --git a/src/backend/catalog/system_views.sql b/src/backend/catalog/system_views.sql
index 53047cab5f..de3d3d8f3e 100644
--- a/src/backend/catalog/system_views.sql
+++ b/src/backend/catalog/system_views.sql
@@ -1358,7 +1358,7 @@ REVOKE ALL ON pg_replication_origin_status FROM public;
 REVOKE ALL ON pg_subscription FROM public;
 GRANT SELECT (oid, subdbid, subskiplsn, subname, subowner, subenabled,
               subbinary, substream, subtwophasestate, subdisableonerr,
-			  subpasswordrequired, subrunasowner, subfailover,
+			  subpasswordrequired, subrunasowner, subfailover, subforcealter,
               subslotname, subsynccommit, subpublications, suborigin)
     ON pg_subscription TO public;
 
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index 97bd11bc4a..7900bb1b28 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -73,6 +73,7 @@
 #define SUBOPT_FAILOVER				0x00002000
 #define SUBOPT_LSN					0x00004000
 #define SUBOPT_ORIGIN				0x00008000
+#define SUBOPT_FORCE_ALTER			0x00010000
 
 /* check if the 'val' has 'bits' set */
 #define IsSet(val, bits)  (((val) & (bits)) == (bits))
@@ -100,6 +101,7 @@ typedef struct SubOpts
 	bool		failover;
 	char	   *origin;
 	XLogRecPtr	lsn;
+	bool		force_alter;
 } SubOpts;
 
 static List *fetch_table_list(WalReceiverConn *wrconn, List *publications);
@@ -162,6 +164,8 @@ parse_subscription_options(ParseState *pstate, List *stmt_options,
 		opts->failover = false;
 	if (IsSet(supported_opts, SUBOPT_ORIGIN))
 		opts->origin = pstrdup(LOGICALREP_ORIGIN_ANY);
+	if (IsSet(supported_opts, SUBOPT_FORCE_ALTER))
+		opts->force_alter = false;
 
 	/* Parse options */
 	foreach(lc, stmt_options)
@@ -367,6 +371,15 @@ parse_subscription_options(ParseState *pstate, List *stmt_options,
 			opts->specified_opts |= SUBOPT_LSN;
 			opts->lsn = lsn;
 		}
+		else if (IsSet(supported_opts, SUBOPT_FORCE_ALTER) &&
+				 strcmp(defel->defname, "force_alter") == 0)
+		{
+			if (IsSet(opts->specified_opts, SUBOPT_FORCE_ALTER))
+				errorConflictingDefElem(defel, pstate);
+
+			opts->specified_opts |= SUBOPT_FORCE_ALTER;
+			opts->force_alter = defGetBoolean(defel);
+		}
 		else
 			ereport(ERROR,
 					(errcode(ERRCODE_SYNTAX_ERROR),
@@ -604,7 +617,8 @@ CreateSubscription(ParseState *pstate, CreateSubscriptionStmt *stmt,
 					  SUBOPT_SYNCHRONOUS_COMMIT | SUBOPT_BINARY |
 					  SUBOPT_STREAMING | SUBOPT_TWOPHASE_COMMIT |
 					  SUBOPT_DISABLE_ON_ERR | SUBOPT_PASSWORD_REQUIRED |
-					  SUBOPT_RUN_AS_OWNER | SUBOPT_FAILOVER | SUBOPT_ORIGIN);
+					  SUBOPT_RUN_AS_OWNER | SUBOPT_FAILOVER | SUBOPT_ORIGIN |
+					  SUBOPT_FORCE_ALTER);
 	parse_subscription_options(pstate, stmt->options, supported_opts, &opts);
 
 	/*
@@ -711,6 +725,7 @@ CreateSubscription(ParseState *pstate, CreateSubscriptionStmt *stmt,
 	values[Anum_pg_subscription_subpasswordrequired - 1] = BoolGetDatum(opts.passwordrequired);
 	values[Anum_pg_subscription_subrunasowner - 1] = BoolGetDatum(opts.runasowner);
 	values[Anum_pg_subscription_subfailover - 1] = BoolGetDatum(opts.failover);
+	values[Anum_pg_subscription_subforcealter] = BoolGetDatum(opts.force_alter);
 	values[Anum_pg_subscription_subconninfo - 1] =
 		CStringGetTextDatum(conninfo);
 	if (opts.slot_name)
@@ -1150,7 +1165,7 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 								  SUBOPT_DISABLE_ON_ERR |
 								  SUBOPT_PASSWORD_REQUIRED |
 								  SUBOPT_RUN_AS_OWNER | SUBOPT_FAILOVER |
-								  SUBOPT_ORIGIN);
+								  SUBOPT_ORIGIN | SUBOPT_FORCE_ALTER);
 
 				parse_subscription_options(pstate, stmt->options,
 										   supported_opts, &opts);
@@ -1204,6 +1219,32 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 						if (sub->twophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
 							(prepared_xacts = GetGidListBySubid(subid)) != NIL)
 						{
+							/*
+							 * Abort prepared transactions only if
+							 * 'force_alter' option is true. Otherwise raise
+							 * an ERROR.
+							 */
+							if (IsSet(opts.specified_opts, SUBOPT_FORCE_ALTER))
+							{
+								if (!opts.force_alter)
+									ereport(ERROR,
+											(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+											 errmsg("cannot alter %s when there are prepared transactions",
+													"two_phase = off"),
+											 errhint("Resolve these transactions or set %s, and then try again.",
+													"force_alter = true")));
+							}
+							else
+							{
+								if (!sub->forcealter)
+									ereport(ERROR,
+											(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+											 errmsg("cannot alter %s when there are prepared transactions",
+													"two_phase = off"),
+											 errhint("Resolve these transactions or set %s, and then try again.",
+													"force_alter = true")));
+							}
+
 							/* Abort all listed transactions */
 							foreach_ptr(char, gid, prepared_xacts)
 								FinishPreparedTransaction(gid, false);
diff --git a/src/bin/pg_dump/pg_dump.c b/src/bin/pg_dump/pg_dump.c
index 5f005a2f14..75b6d1693e 100644
--- a/src/bin/pg_dump/pg_dump.c
+++ b/src/bin/pg_dump/pg_dump.c
@@ -4739,6 +4739,7 @@ getSubscriptions(Archive *fout)
 	int			i_suboriginremotelsn;
 	int			i_subenabled;
 	int			i_subfailover;
+	int			i_subforcealter;
 	int			i,
 				ntups;
 
@@ -4816,6 +4817,14 @@ getSubscriptions(Archive *fout)
 		appendPQExpBuffer(query,
 						  " false AS subfailover\n");
 
+	if (fout->remoteVersion >= 170000)
+		appendPQExpBufferStr(query,
+							 " s.subforcealter\n");
+	else
+		appendPQExpBuffer(query,
+						  " false AS subforcealter\n");
+
+
 	appendPQExpBufferStr(query,
 						 "FROM pg_subscription s\n");
 
@@ -4854,6 +4863,7 @@ getSubscriptions(Archive *fout)
 	i_suboriginremotelsn = PQfnumber(res, "suboriginremotelsn");
 	i_subenabled = PQfnumber(res, "subenabled");
 	i_subfailover = PQfnumber(res, "subfailover");
+	i_subforcealter = PQfnumber(res, "subforcealter");
 
 	subinfo = pg_malloc(ntups * sizeof(SubscriptionInfo));
 
@@ -4900,6 +4910,8 @@ getSubscriptions(Archive *fout)
 			pg_strdup(PQgetvalue(res, i, i_subenabled));
 		subinfo[i].subfailover =
 			pg_strdup(PQgetvalue(res, i, i_subfailover));
+		subinfo[i].subforcealter =
+			pg_strdup(PQgetvalue(res, i, i_subforcealter));
 
 		/* Decide whether we want to dump it */
 		selectDumpableObject(&(subinfo[i].dobj), fout);
@@ -5140,6 +5152,9 @@ dumpSubscription(Archive *fout, const SubscriptionInfo *subinfo)
 	if (strcmp(subinfo->subfailover, "t") == 0)
 		appendPQExpBufferStr(query, ", failover = true");
 
+	if (strcmp(subinfo->subforcealter, "t") == 0)
+		appendPQExpBufferStr(query, ", force_alter = true");
+
 	if (strcmp(subinfo->subsynccommit, "off") != 0)
 		appendPQExpBuffer(query, ", synchronous_commit = %s", fmtId(subinfo->subsynccommit));
 
diff --git a/src/bin/pg_dump/pg_dump.h b/src/bin/pg_dump/pg_dump.h
index 2a7c5873a0..0e85ee311b 100644
--- a/src/bin/pg_dump/pg_dump.h
+++ b/src/bin/pg_dump/pg_dump.h
@@ -677,6 +677,7 @@ typedef struct _SubscriptionInfo
 	char	   *suborigin;
 	char	   *suboriginremotelsn;
 	char	   *subfailover;
+	char	   *subforcealter;
 } SubscriptionInfo;
 
 /*
diff --git a/src/bin/psql/describe.c b/src/bin/psql/describe.c
index 4a9ee4a54d..86f099ba57 100644
--- a/src/bin/psql/describe.c
+++ b/src/bin/psql/describe.c
@@ -6581,7 +6581,7 @@ describeSubscriptions(const char *pattern, bool verbose)
 	printQueryOpt myopt = pset.popt;
 	static const bool translate_columns[] = {false, false, false, false,
 		false, false, false, false, false, false, false, false, false, false,
-	false};
+	false, false};
 
 	if (pset.sversion < 100000)
 	{
@@ -6650,6 +6650,11 @@ describeSubscriptions(const char *pattern, bool verbose)
 							  ", subfailover AS \"%s\"\n",
 							  gettext_noop("Failover"));
 
+		if (pset.sversion >= 170000)
+			appendPQExpBuffer(&buf,
+							  ", subforcealter AS \"%s\"\n",
+							  gettext_noop("Force_alter"));
+
 		appendPQExpBuffer(&buf,
 						  ",  subsynccommit AS \"%s\"\n"
 						  ",  subconninfo AS \"%s\"\n",
diff --git a/src/include/catalog/pg_subscription.h b/src/include/catalog/pg_subscription.h
index 0aa14ec4a2..208e540f80 100644
--- a/src/include/catalog/pg_subscription.h
+++ b/src/include/catalog/pg_subscription.h
@@ -98,6 +98,9 @@ CATALOG(pg_subscription,6100,SubscriptionRelationId) BKI_SHARED_RELATION BKI_ROW
 								 * slots) in the upstream database are enabled
 								 * to be synchronized to the standbys. */
 
+	bool		subforcealter;	/* True if we allow to drop prepared transactions
+								 * when altering two_phase "on"->"off". */
+
 #ifdef CATALOG_VARLEN			/* variable-length fields start here */
 	/* Connection string to the publisher */
 	text		subconninfo BKI_FORCE_NOT_NULL;
@@ -151,6 +154,9 @@ typedef struct Subscription
 								 * (i.e. the main slot and the table sync
 								 * slots) in the upstream database are enabled
 								 * to be synchronized to the standbys. */
+	bool		forcealter;		/* True if we allow to drop prepared
+								 * transactions when altering two_phase
+								 * "on"->"off". */
 	char	   *conninfo;		/* Connection string to the publisher */
 	char	   *slotname;		/* Name of the replication slot */
 	char	   *synccommit;		/* Synchronous commit setting for worker */
diff --git a/src/test/regress/expected/subscription.out b/src/test/regress/expected/subscription.out
index 51fa4b9690..5100309d35 100644
--- a/src/test/regress/expected/subscription.out
+++ b/src/test/regress/expected/subscription.out
@@ -116,18 +116,18 @@ CREATE SUBSCRIPTION regress_testsub4 CONNECTION 'dbname=regress_doesnotexist' PU
 WARNING:  subscription was created, but is not connected
 HINT:  To initiate replication, you must manually create the replication slot, enable the subscription, and refresh the subscription.
 \dRs+ regress_testsub4
-                                                                                                                 List of subscriptions
-       Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
-------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub4 | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | none   | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                        List of subscriptions
+       Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force_alter | Synchronous commit |          Conninfo           | Skip LSN 
+------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub4 | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | none   | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub4 SET (origin = any);
 \dRs+ regress_testsub4
-                                                                                                                 List of subscriptions
-       Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
-------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub4 | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                        List of subscriptions
+       Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force_alter | Synchronous commit |          Conninfo           | Skip LSN 
+------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub4 | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 DROP SUBSCRIPTION regress_testsub3;
@@ -145,10 +145,10 @@ ALTER SUBSCRIPTION regress_testsub CONNECTION 'foobar';
 ERROR:  invalid connection string syntax: missing "=" after "foobar" in connection info string
 
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force_alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET PUBLICATION testpub2, testpub3 WITH (refresh = false);
@@ -157,10 +157,10 @@ ALTER SUBSCRIPTION regress_testsub SET (slot_name = 'newname');
 ALTER SUBSCRIPTION regress_testsub SET (password_required = false);
 ALTER SUBSCRIPTION regress_testsub SET (run_as_owner = true);
 \dRs+
-                                                                                                                     List of subscriptions
-      Name       |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |           Conninfo           | Skip LSN 
------------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+------------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | f                 | t             | f        | off                | dbname=regress_doesnotexist2 | 0/0
+                                                                                                                            List of subscriptions
+      Name       |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force_alter | Synchronous commit |           Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+------------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | f                 | t             | f        | f           | off                | dbname=regress_doesnotexist2 | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (password_required = true);
@@ -176,10 +176,10 @@ ERROR:  unrecognized subscription parameter: "create_slot"
 -- ok
 ALTER SUBSCRIPTION regress_testsub SKIP (lsn = '0/12345');
 \dRs+
-                                                                                                                     List of subscriptions
-      Name       |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |           Conninfo           | Skip LSN 
------------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+------------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist2 | 0/12345
+                                                                                                                            List of subscriptions
+      Name       |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force_alter | Synchronous commit |           Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+------------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist2 | 0/12345
 (1 row)
 
 -- ok - with lsn = NONE
@@ -188,10 +188,10 @@ ALTER SUBSCRIPTION regress_testsub SKIP (lsn = NONE);
 ALTER SUBSCRIPTION regress_testsub SKIP (lsn = '0/0');
 ERROR:  invalid WAL location (LSN): 0/0
 \dRs+
-                                                                                                                     List of subscriptions
-      Name       |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |           Conninfo           | Skip LSN 
------------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+------------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist2 | 0/0
+                                                                                                                            List of subscriptions
+      Name       |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force_alter | Synchronous commit |           Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+------------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist2 | 0/0
 (1 row)
 
 BEGIN;
@@ -223,10 +223,10 @@ ALTER SUBSCRIPTION regress_testsub_foo SET (synchronous_commit = foobar);
 ERROR:  invalid value for parameter "synchronous_commit": "foobar"
 HINT:  Available values: local, remote_write, remote_apply, on, off.
 \dRs+
-                                                                                                                       List of subscriptions
-        Name         |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |           Conninfo           | Skip LSN 
----------------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+------------------------------+----------
- regress_testsub_foo | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | t                 | f             | f        | local              | dbname=regress_doesnotexist2 | 0/0
+                                                                                                                              List of subscriptions
+        Name         |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force_alter | Synchronous commit |           Conninfo           | Skip LSN 
+---------------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+------------------------------+----------
+ regress_testsub_foo | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | t                 | f             | f        | f           | local              | dbname=regress_doesnotexist2 | 0/0
 (1 row)
 
 -- rename back to keep the rest simple
@@ -255,19 +255,19 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 WARNING:  subscription was created, but is not connected
 HINT:  To initiate replication, you must manually create the replication slot, enable the subscription, and refresh the subscription.
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | t      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force_alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | t      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (binary = false);
 ALTER SUBSCRIPTION regress_testsub SET (slot_name = NONE);
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force_alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 DROP SUBSCRIPTION regress_testsub;
@@ -279,27 +279,27 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 WARNING:  subscription was created, but is not connected
 HINT:  To initiate replication, you must manually create the replication slot, enable the subscription, and refresh the subscription.
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | on        | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force_alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | on        | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (streaming = parallel);
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | parallel  | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force_alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | parallel  | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (streaming = false);
 ALTER SUBSCRIPTION regress_testsub SET (slot_name = NONE);
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force_alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 -- fail - publication already exists
@@ -314,10 +314,10 @@ ALTER SUBSCRIPTION regress_testsub ADD PUBLICATION testpub1, testpub2 WITH (refr
 ALTER SUBSCRIPTION regress_testsub ADD PUBLICATION testpub1, testpub2 WITH (refresh = false);
 ERROR:  publication "testpub1" is already in subscription "regress_testsub"
 \dRs+
-                                                                                                                        List of subscriptions
-      Name       |           Owner           | Enabled |         Publication         | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-----------------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub,testpub1,testpub2} | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                               List of subscriptions
+      Name       |           Owner           | Enabled |         Publication         | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force_alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-----------------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub,testpub1,testpub2} | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 -- fail - publication used more than once
@@ -332,10 +332,10 @@ ERROR:  publication "testpub3" is not in subscription "regress_testsub"
 -- ok - delete publications
 ALTER SUBSCRIPTION regress_testsub DROP PUBLICATION testpub1, testpub2 WITH (refresh = false);
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force_alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 DROP SUBSCRIPTION regress_testsub;
@@ -371,19 +371,19 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 WARNING:  subscription was created, but is not connected
 HINT:  To initiate replication, you must manually create the replication slot, enable the subscription, and refresh the subscription.
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | p                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force_alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | p                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 -- We can alter streaming when two_phase enabled
 ALTER SUBSCRIPTION regress_testsub SET (streaming = true);
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | on        | p                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force_alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | on        | p                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (slot_name = NONE);
@@ -393,10 +393,10 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 WARNING:  subscription was created, but is not connected
 HINT:  To initiate replication, you must manually create the replication slot, enable the subscription, and refresh the subscription.
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | on        | p                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force_alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | on        | p                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (slot_name = NONE);
@@ -409,18 +409,18 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 WARNING:  subscription was created, but is not connected
 HINT:  To initiate replication, you must manually create the replication slot, enable the subscription, and refresh the subscription.
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force_alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (disable_on_error = true);
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | t                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force_alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | t                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (slot_name = NONE);
diff --git a/src/test/subscription/t/099_twophase_added.pl b/src/test/subscription/t/099_twophase_added.pl
index 9cc1ca9167..22b4f2d9a0 100644
--- a/src/test/subscription/t/099_twophase_added.pl
+++ b/src/test/subscription/t/099_twophase_added.pl
@@ -97,7 +97,8 @@ is($result, q(5),
 # Check the case that prepared transactions exist on the subscriber node
 #
 # If the two_phase is altering from "on" to "off" and there are prepared
-# transactions on the subscriber, they must be aborted. This test checks it.
+# transactions on the subscriber, we must error out or abort all prepared
+# transactions. Below part checks both cases.
 
 # Prepare a transaction to insert some tuples into the table
 $node_publisher->safe_psql(
@@ -114,15 +115,39 @@ $result = $node_subscriber->safe_psql('postgres',
     "SELECT count(*) FROM pg_prepared_xacts;");
 is($result, q(1), "transaction has been prepared on subscriber");
 
-# Toggle the two_phase to "off" before the COMMIT PREPARED
-$node_subscriber->safe_psql(
-    'postgres', "
-    ALTER SUBSCRIPTION regress_sub DISABLE;
-    ALTER SUBSCRIPTION regress_sub SET (two_phase = off);
-    ALTER SUBSCRIPTION regress_sub ENABLE;");
+# Disable the subscription to alter the two_phase option
+$node_subscriber->safe_psql('postgres', "ALTER SUBSCRIPTION regress_sub DISABLE;");
+
+# Try altering the two_phase option to "off." The command will fail since there
+# is a prepared transaction and the 'force_alter' option is not specified as
+# true.
+my $stdout;
+my $stderr;
+
+($result, $stdout, $stderr) = $node_subscriber->psql(
+	'postgres', "ALTER SUBSCRIPTION regress_sub SET (two_phase = off);");
+ok($stderr =~ /cannot alter two_phase = off when there are prepared transactions/,
+	'ALTER SUBSCRIPTION failed');
+
+# Verify the prepared transaction still exists
+$result = $node_subscriber->safe_psql('postgres',
+    "SELECT count(*) FROM pg_prepared_xacts;");
+is($result, q(1), "prepared transaction still exists");
+
+$log_offset = -s $node_subscriber->logfile;
+
+# Alter the two_phase with the force_alter option. Apart from the the last
+# ALTER SUBSCRIPTION command, the command will abort the prepared transaction
+# and succeed.
+$node_subscriber->safe_psql('postgres',
+    "ALTER SUBSCRIPTION regress_sub SET (two_phase = off, force_alter = true);");
+$node_subscriber->safe_psql('postgres', "ALTER SUBSCRIPTION regress_sub ENABLE;");
+
+# Verify the started worker recognized two_phase was disabled
+$node_subscriber->wait_for_log(
+	'logical replication apply worker for subscription "regress_sub" two_phase is DISABLED', $log_offset);
 
-# Verify any prepared transactions are aborted because two_phase is changed to
-# "off".
+# Verify the prepared transaction was aborted
 $result = $node_subscriber->safe_psql('postgres',
     "SELECT count(*) FROM pg_prepared_xacts;");
 is($result, q(0), "prepared transaction done by worker is aborted");
-- 
2.43.0

From 99884858e2b31329f19b7384d811bfd334245471 Mon Sep 17 00:00:00 2001
From: Ajin Cherian <ajinc@fast.au.fujitsu.com>
Date: Fri, 5 Apr 2024 06:47:18 -0400
Subject: [PATCH v10 1/4] Allow altering of two_phase option of a SUBSCRIPTION

This patch allows the user to alter the 'two_phase' option of a subscriber provided no
uncommitted prepared transactions are pending on that subscription.

Author: Cherian Ajin, Hayato Kuroda
---
 doc/src/sgml/ref/alter_subscription.sgml      | 12 ++--
 src/backend/access/transam/twophase.c         | 62 ++++++++++++++++
 src/backend/commands/subscriptioncmds.c       | 67 +++++++++++++----
 .../libpqwalreceiver/libpqwalreceiver.c       |  9 +--
 src/backend/replication/logical/launcher.c    | 22 ++++++
 src/backend/replication/logical/worker.c      | 21 +-----
 src/backend/replication/slot.c                | 18 ++++-
 src/backend/replication/walsender.c           | 18 ++++-
 src/bin/psql/tab-complete.c                   |  2 +-
 src/include/access/twophase.h                 |  5 ++
 src/include/replication/slot.h                |  3 +-
 src/include/replication/walreceiver.h         | 11 +--
 src/include/replication/worker_internal.h     |  1 +
 src/test/regress/expected/subscription.out    |  5 +-
 src/test/regress/sql/subscription.sql         |  5 +-
 src/test/subscription/t/021_twophase.pl       | 71 ++++++++++++++++++-
 16 files changed, 269 insertions(+), 63 deletions(-)

diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index a78c1c3a47..88e9a72147 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -68,8 +68,9 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
   <para>
    Commands <command>ALTER SUBSCRIPTION ... REFRESH PUBLICATION</command>,
    <command>ALTER SUBSCRIPTION ... {SET|ADD|DROP} PUBLICATION ...</command>
-   with <literal>refresh</literal> option as <literal>true</literal> and
-   <command>ALTER SUBSCRIPTION ... SET (failover = on|off)</command>
+   with <literal>refresh</literal> option as <literal>true</literal>,
+   <command>ALTER SUBSCRIPTION ... SET (failover = on|off)</command> and
+   <command>ALTER SUBSCRIPTION ... SET (two_phase = on|off)</command>
    cannot be executed inside a transaction block.
 
    These commands also cannot be executed when the subscription has
@@ -228,9 +229,12 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-disable-on-error"><literal>disable_on_error</literal></link>,
       <link linkend="sql-createsubscription-params-with-password-required"><literal>password_required</literal></link>,
       <link linkend="sql-createsubscription-params-with-run-as-owner"><literal>run_as_owner</literal></link>,
-      <link linkend="sql-createsubscription-params-with-origin"><literal>origin</literal></link>, and
-      <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>.
+      <link linkend="sql-createsubscription-params-with-origin"><literal>origin</literal></link>,
+      <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>, and
+      <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>.
       Only a superuser can set <literal>password_required = false</literal>.
+      The <literal>two_phase</literal> parameter can only be altered when the
+      subscription is disabled.
      </para>
 
      <para>
diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index 8090ac9fc1..66fa591eb5 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -2682,3 +2682,65 @@ LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 	LWLockRelease(TwoPhaseStateLock);
 	return found;
 }
+
+/*
+ * TwoPhaseTransactionGid
+ *		Form the prepared transaction GID for two_phase transactions.
+ *
+ * Return the GID in the supplied buffer.
+ */
+void
+TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid, int szgid)
+{
+	Assert(subid != InvalidRepOriginId);
+
+	if (!TransactionIdIsValid(xid))
+		ereport(ERROR,
+				(errcode(ERRCODE_PROTOCOL_VIOLATION),
+				 errmsg_internal("invalid two-phase transaction ID")));
+
+	snprintf(gid, szgid, "pg_gid_%u_%u", subid, xid);
+}
+
+/*
+ * IsTwoPhaseTransactionGidForSubid
+ *		Check whether the given GID (as formed by TwoPhaseTransactionGid) is
+ *		for the specified 'subid'.
+ */
+static bool
+IsTwoPhaseTransactionGidForSubid(Oid subid, char *gid)
+{
+	int				ret;
+	Oid				subid_written;
+	TransactionId	xid;
+
+	ret = sscanf(gid, "pg_gid_%u_%u", &subid_written, &xid);
+
+	return (ret == 2 && subid == subid_written);
+}
+
+/*
+ * LookupGXactBySubid
+ *		Check if the prepared transaction done by apply worker exists.
+ */
+bool
+LookupGXactBySubid(Oid subid)
+{
+	bool		found = false;
+
+	LWLockAcquire(TwoPhaseStateLock, LW_SHARED);
+	for (int i = 0; i < TwoPhaseState->numPrepXacts; i++)
+	{
+		GlobalTransaction gxact = TwoPhaseState->prepXacts[i];
+
+		/* Ignore not-yet-valid GIDs. */
+		if (gxact->valid &&
+			IsTwoPhaseTransactionGidForSubid(subid, gxact->gid))
+		{
+			found = true;
+			break;
+		}
+	}
+	LWLockRelease(TwoPhaseStateLock);
+	return found;
+}
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index e407428dbc..90d967eb7c 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -16,6 +16,7 @@
 
 #include "access/htup_details.h"
 #include "access/table.h"
+#include "access/twophase.h"
 #include "access/xact.h"
 #include "catalog/catalog.h"
 #include "catalog/dependency.h"
@@ -1143,7 +1144,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 			{
 				supported_opts = (SUBOPT_SLOT_NAME |
 								  SUBOPT_SYNCHRONOUS_COMMIT | SUBOPT_BINARY |
-								  SUBOPT_STREAMING | SUBOPT_DISABLE_ON_ERR |
+								  SUBOPT_STREAMING | SUBOPT_TWOPHASE_COMMIT |
+								  SUBOPT_DISABLE_ON_ERR |
 								  SUBOPT_PASSWORD_REQUIRED |
 								  SUBOPT_RUN_AS_OWNER | SUBOPT_FAILOVER |
 								  SUBOPT_ORIGIN);
@@ -1151,6 +1153,52 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 				parse_subscription_options(pstate, stmt->options,
 										   supported_opts, &opts);
 
+				if (IsSet(opts.specified_opts, SUBOPT_TWOPHASE_COMMIT))
+				{
+					/*
+					 * Do not allow changing the two_phase option if the
+					 * subscription is enabled. This is because the two_phase
+					 * option of the slot on the publisher cannot be modified
+					 * if the slot is currently acquired by the apply worker.
+					 */
+					if (form->subenabled)
+						ereport(ERROR,
+								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+								 errmsg("cannot set %s for enabled subscription",
+										"two_phase")));
+
+					/*
+					 * Stop all the subscription workers, just in case. Workers
+					 * may still survive even if the subscription is disabled.
+					 */
+					logicalrep_workers_stop(subid);
+
+					/*
+					 * two_phase cannot be disabled if there are any
+					 * uncommitted prepared transactions present.
+					 */
+					if (!opts.twophase &&
+						form->subtwophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
+						LookupGXactBySubid(subid))
+						ereport(ERROR,
+								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+								 errmsg("cannot disable two_phase when uncommitted prepared transactions present"),
+								 errhint("Resolve these transactions and try again")));
+
+					/*
+					 * The changed two_phase option of the slot can't be rolled
+					 * back.
+					 */
+					PreventInTransactionBlock(isTopLevel, "ALTER SUBSCRIPTION ... SET (two_phase)");
+
+					/* Change system catalog acoordingly */
+					values[Anum_pg_subscription_subtwophasestate - 1] =
+						CharGetDatum(opts.twophase ?
+									 LOGICALREP_TWOPHASE_STATE_PENDING :
+									 LOGICALREP_TWOPHASE_STATE_DISABLED);
+					replaces[Anum_pg_subscription_subtwophasestate - 1] = true;
+				}
+
 				if (IsSet(opts.specified_opts, SUBOPT_SLOT_NAME))
 				{
 					/*
@@ -1505,7 +1553,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 	 * doing the database operations we won't be able to rollback altered
 	 * slot.
 	 */
-	if (replaces[Anum_pg_subscription_subfailover - 1])
+	if (replaces[Anum_pg_subscription_subfailover - 1] ||
+		replaces[Anum_pg_subscription_subtwophasestate - 1])
 	{
 		bool		must_use_password;
 		char	   *err;
@@ -1525,7 +1574,7 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 
 		PG_TRY();
 		{
-			walrcv_alter_slot(wrconn, sub->slotname, opts.failover);
+			walrcv_alter_slot(wrconn, sub->slotname, opts.failover, opts.twophase);
 		}
 		PG_FINALLY();
 		{
@@ -1562,7 +1611,6 @@ DropSubscription(DropSubscriptionStmt *stmt, bool isTopLevel)
 	char	   *subname;
 	char	   *conninfo;
 	char	   *slotname;
-	List	   *subworkers;
 	ListCell   *lc;
 	char		originname[NAMEDATALEN];
 	char	   *err = NULL;
@@ -1672,16 +1720,7 @@ DropSubscription(DropSubscriptionStmt *stmt, bool isTopLevel)
 	 * New workers won't be started because we hold an exclusive lock on the
 	 * subscription till the end of the transaction.
 	 */
-	LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
-	subworkers = logicalrep_workers_find(subid, false);
-	LWLockRelease(LogicalRepWorkerLock);
-	foreach(lc, subworkers)
-	{
-		LogicalRepWorker *w = (LogicalRepWorker *) lfirst(lc);
-
-		logicalrep_worker_stop(w->subid, w->relid);
-	}
-	list_free(subworkers);
+	logicalrep_workers_stop(subid);
 
 	/*
 	 * Remove the no-longer-useful entry in the launcher's table of apply
diff --git a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
index 3c2b1bb496..998bbd517a 100644
--- a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
+++ b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
@@ -80,7 +80,7 @@ static char *libpqrcv_create_slot(WalReceiverConn *conn,
 								  CRSSnapshotAction snapshot_action,
 								  XLogRecPtr *lsn);
 static void libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-								bool failover);
+								bool failover, bool two_phase);
 static pid_t libpqrcv_get_backend_pid(WalReceiverConn *conn);
 static WalRcvExecResult *libpqrcv_exec(WalReceiverConn *conn,
 									   const char *query,
@@ -1121,15 +1121,16 @@ libpqrcv_create_slot(WalReceiverConn *conn, const char *slotname,
  */
 static void
 libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-					bool failover)
+					bool failover, bool two_phase)
 {
 	StringInfoData cmd;
 	PGresult   *res;
 
 	initStringInfo(&cmd);
-	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( FAILOVER %s )",
+	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( FAILOVER %s, TWO_PHASE %s )",
 					 quote_identifier(slotname),
-					 failover ? "true" : "false");
+					 failover ? "true" : "false",
+					 two_phase ? "true" : "false");
 
 	res = libpqrcv_PQexec(conn->streamConn, cmd.data);
 	pfree(cmd.data);
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 66070e9131..548f6e0edb 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -623,6 +623,28 @@ logicalrep_worker_stop(Oid subid, Oid relid)
 	LWLockRelease(LogicalRepWorkerLock);
 }
 
+/*
+ * Stop all the subscription workers.
+ */
+void
+logicalrep_workers_stop(Oid subid)
+{
+	List	   *subworkers;
+	ListCell   *lc;
+
+	LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
+	/* XXX clarify the reason why not only running workers are listed. */
+	subworkers = logicalrep_workers_find(subid, false);
+	LWLockRelease(LogicalRepWorkerLock);
+	foreach(lc, subworkers)
+	{
+		LogicalRepWorker *w = (LogicalRepWorker *) lfirst(lc);
+
+		logicalrep_worker_stop(w->subid, w->relid);
+	}
+	list_free(subworkers);
+}
+
 /*
  * Stop the given logical replication parallel apply worker.
  *
diff --git a/src/backend/replication/logical/worker.c b/src/backend/replication/logical/worker.c
index b5a80fe3e8..dcf656fd45 100644
--- a/src/backend/replication/logical/worker.c
+++ b/src/backend/replication/logical/worker.c
@@ -402,7 +402,6 @@ static void apply_handle_tuple_routing(ApplyExecutionData *edata,
 									   CmdType operation);
 
 /* Compute GID for two_phase transactions */
-static void TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid, int szgid);
 
 /* Functions for skipping changes */
 static void maybe_start_skipping_changes(XLogRecPtr finish_lsn);
@@ -3911,7 +3910,7 @@ maybe_reread_subscription(void)
 	/* !slotname should never happen when enabled is true. */
 	Assert(newsub->slotname);
 
-	/* two-phase should not be altered */
+	/* two-phase cannot be altered while the worker exists */
 	Assert(newsub->twophasestate == MySubscription->twophasestate);
 
 	/*
@@ -4396,24 +4395,6 @@ cleanup_subxact_info()
 	subxact_data.nsubxacts_max = 0;
 }
 
-/*
- * Form the prepared transaction GID for two_phase transactions.
- *
- * Return the GID in the supplied buffer.
- */
-static void
-TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid, int szgid)
-{
-	Assert(subid != InvalidRepOriginId);
-
-	if (!TransactionIdIsValid(xid))
-		ereport(ERROR,
-				(errcode(ERRCODE_PROTOCOL_VIOLATION),
-				 errmsg_internal("invalid two-phase transaction ID")));
-
-	snprintf(gid, szgid, "pg_gid_%u_%u", subid, xid);
-}
-
 /*
  * Common function to run the apply loop with error handling. Disable the
  * subscription, if necessary.
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index aa4ea387da..d0c8d5a4df 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -804,8 +804,10 @@ ReplicationSlotDrop(const char *name, bool nowait)
  * Change the definition of the slot identified by the specified name.
  */
 void
-ReplicationSlotAlter(const char *name, bool failover)
+ReplicationSlotAlter(const char *name, bool failover, bool two_phase)
 {
+	bool		update_slot = false;
+
 	Assert(MyReplicationSlot == NULL);
 
 	ReplicationSlotAcquire(name, false);
@@ -854,6 +856,20 @@ ReplicationSlotAlter(const char *name, bool failover)
 		MyReplicationSlot->data.failover = failover;
 		SpinLockRelease(&MyReplicationSlot->mutex);
 
+		update_slot = true;
+	}
+
+	if (MyReplicationSlot->data.two_phase != two_phase)
+	{
+		SpinLockAcquire(&MyReplicationSlot->mutex);
+		MyReplicationSlot->data.two_phase = two_phase;
+		SpinLockRelease(&MyReplicationSlot->mutex);
+
+		update_slot = true;
+	}
+
+	if (update_slot)
+	{
 		ReplicationSlotMarkDirty();
 		ReplicationSlotSave();
 	}
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index c623b07cf0..2e6ca35049 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1411,9 +1411,11 @@ DropReplicationSlot(DropReplicationSlotCmd *cmd)
  * Process extra options given to ALTER_REPLICATION_SLOT.
  */
 static void
-ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd, bool *failover)
+ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd,
+						  bool *failover, bool *two_phase)
 {
 	bool		failover_given = false;
+	bool		two_phase_given = false;
 
 	/* Parse options */
 	foreach_ptr(DefElem, defel, cmd->options)
@@ -1427,6 +1429,15 @@ ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd, bool *failover)
 			failover_given = true;
 			*failover = defGetBoolean(defel);
 		}
+		else if (strcmp(defel->defname, "two_phase") == 0)
+		{
+			if (two_phase_given)
+				ereport(ERROR,
+						(errcode(ERRCODE_SYNTAX_ERROR),
+						 errmsg("conflicting or redundant options")));
+			two_phase_given = true;
+			*two_phase = defGetBoolean(defel);
+		}
 		else
 			elog(ERROR, "unrecognized option: %s", defel->defname);
 	}
@@ -1439,9 +1450,10 @@ static void
 AlterReplicationSlot(AlterReplicationSlotCmd *cmd)
 {
 	bool		failover = false;
+	bool		two_phase = false;
 
-	ParseAlterReplSlotOptions(cmd, &failover);
-	ReplicationSlotAlter(cmd->slotname, failover);
+	ParseAlterReplSlotOptions(cmd, &failover, &two_phase);
+	ReplicationSlotAlter(cmd->slotname, failover, two_phase);
 }
 
 /*
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
index d453e224d9..891face1b6 100644
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -1948,7 +1948,7 @@ psql_completion(const char *text, int start, int end)
 	else if (HeadMatches("ALTER", "SUBSCRIPTION", MatchAny) && TailMatches("SET", "("))
 		COMPLETE_WITH("binary", "disable_on_error", "failover", "origin",
 					  "password_required", "run_as_owner", "slot_name",
-					  "streaming", "synchronous_commit");
+					  "streaming", "synchronous_commit", "two_phase");
 	/* ALTER SUBSCRIPTION <name> SKIP ( */
 	else if (HeadMatches("ALTER", "SUBSCRIPTION", MatchAny) && TailMatches("SKIP", "("))
 		COMPLETE_WITH("lsn");
diff --git a/src/include/access/twophase.h b/src/include/access/twophase.h
index 56248c0006..d37e06fdee 100644
--- a/src/include/access/twophase.h
+++ b/src/include/access/twophase.h
@@ -62,4 +62,9 @@ extern void PrepareRedoRemove(TransactionId xid, bool giveWarning);
 extern void restoreTwoPhaseData(void);
 extern bool LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 						TimestampTz origin_prepare_timestamp);
+
+extern void TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid,
+								   int szgid);
+extern bool LookupGXactBySubid(Oid subid);
+
 #endif							/* TWOPHASE_H */
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 1bc80960ef..014e216cf5 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -243,7 +243,8 @@ extern void ReplicationSlotCreate(const char *name, bool db_specific,
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
 extern void ReplicationSlotDropAcquired(void);
-extern void ReplicationSlotAlter(const char *name, bool failover);
+extern void ReplicationSlotAlter(const char *name, bool failover,
+								 bool two_phase);
 
 extern void ReplicationSlotAcquire(const char *name, bool nowait);
 extern void ReplicationSlotRelease(void);
diff --git a/src/include/replication/walreceiver.h b/src/include/replication/walreceiver.h
index 12f71fa99b..31fa1257ec 100644
--- a/src/include/replication/walreceiver.h
+++ b/src/include/replication/walreceiver.h
@@ -372,12 +372,13 @@ typedef char *(*walrcv_create_slot_fn) (WalReceiverConn *conn,
 /*
  * walrcv_alter_slot_fn
  *
- * Change the definition of a replication slot. Currently, it only supports
- * changing the failover property of the slot.
+ * Change the definition of a replication slot. Currently, it supports
+ * changing the failover and the two_phase property of the slot.
  */
 typedef void (*walrcv_alter_slot_fn) (WalReceiverConn *conn,
 									  const char *slotname,
-									  bool failover);
+									  bool failover,
+									  bool two_phase);
 
 /*
  * walrcv_get_backend_pid_fn
@@ -455,8 +456,8 @@ extern PGDLLIMPORT WalReceiverFunctionsType *WalReceiverFunctions;
 	WalReceiverFunctions->walrcv_send(conn, buffer, nbytes)
 #define walrcv_create_slot(conn, slotname, temporary, two_phase, failover, snapshot_action, lsn) \
 	WalReceiverFunctions->walrcv_create_slot(conn, slotname, temporary, two_phase, failover, snapshot_action, lsn)
-#define walrcv_alter_slot(conn, slotname, failover) \
-	WalReceiverFunctions->walrcv_alter_slot(conn, slotname, failover)
+#define walrcv_alter_slot(conn, slotname, failover, two_phase) \
+	WalReceiverFunctions->walrcv_alter_slot(conn, slotname, failover, two_phase)
 #define walrcv_get_backend_pid(conn) \
 	WalReceiverFunctions->walrcv_get_backend_pid(conn)
 #define walrcv_exec(conn, exec, nRetTypes, retTypes) \
diff --git a/src/include/replication/worker_internal.h b/src/include/replication/worker_internal.h
index 515aefd519..d5428263c1 100644
--- a/src/include/replication/worker_internal.h
+++ b/src/include/replication/worker_internal.h
@@ -246,6 +246,7 @@ extern bool logicalrep_worker_launch(LogicalRepWorkerType wtype,
 									 Oid userid, Oid relid,
 									 dsm_handle subworker_dsm);
 extern void logicalrep_worker_stop(Oid subid, Oid relid);
+extern void logicalrep_workers_stop(Oid subid);
 extern void logicalrep_pa_worker_stop(ParallelApplyWorkerInfo *winfo);
 extern void logicalrep_worker_wakeup(Oid subid, Oid relid);
 extern void logicalrep_worker_wakeup_ptr(LogicalRepWorker *worker);
diff --git a/src/test/regress/expected/subscription.out b/src/test/regress/expected/subscription.out
index 0f2a25cdc1..51fa4b9690 100644
--- a/src/test/regress/expected/subscription.out
+++ b/src/test/regress/expected/subscription.out
@@ -377,10 +377,7 @@ HINT:  To initiate replication, you must manually create the replication slot, e
  regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | p                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
---fail - alter of two_phase option not supported.
-ALTER SUBSCRIPTION regress_testsub SET (two_phase = false);
-ERROR:  unrecognized subscription parameter: "two_phase"
--- but can alter streaming when two_phase enabled
+-- We can alter streaming when two_phase enabled
 ALTER SUBSCRIPTION regress_testsub SET (streaming = true);
 \dRs+
                                                                                                                 List of subscriptions
diff --git a/src/test/regress/sql/subscription.sql b/src/test/regress/sql/subscription.sql
index 3e5ba4cb8c..a3886d79ca 100644
--- a/src/test/regress/sql/subscription.sql
+++ b/src/test/regress/sql/subscription.sql
@@ -256,10 +256,7 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUBLICATION testpub WITH (connect = false, two_phase = true);
 
 \dRs+
---fail - alter of two_phase option not supported.
-ALTER SUBSCRIPTION regress_testsub SET (two_phase = false);
-
--- but can alter streaming when two_phase enabled
+-- We can alter streaming when two_phase enabled
 ALTER SUBSCRIPTION regress_testsub SET (streaming = true);
 
 \dRs+
diff --git a/src/test/subscription/t/021_twophase.pl b/src/test/subscription/t/021_twophase.pl
index 9437cd4c3b..72df258000 100644
--- a/src/test/subscription/t/021_twophase.pl
+++ b/src/test/subscription/t/021_twophase.pl
@@ -367,6 +367,75 @@ $result =
   $node_subscriber->safe_psql('postgres', "SELECT count(*) FROM tab_copy;");
 is($result, qq(2), 'replicated data in subscriber table');
 
+# Clean up
+$node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub");
+
+###############################
+# Disable the subscription and alter it to two_phase = false,
+# then verify that the altered subscription reflects the two_phase option.
+###############################
+
+# Alter subscription two_phase to false
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy DISABLE");
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = false)");
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy ENABLE");
+
+# Wait for subscription startup
+$node_subscriber->wait_for_subscription_sync($node_publisher, $appname_copy);
+
+# Make sure that the two-phase is disabled on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+       "SELECT subtwophasestate FROM pg_subscription WHERE subname = 'tap_sub_copy';"
+);
+is($result, qq(d), 'two-phase should be disabled');
+
+# Now do a prepare on the publisher and make sure that it is not replicated.
+$node_publisher->safe_psql(
+       'postgres', qq{
+    BEGIN;
+    INSERT INTO tab_copy VALUES (100);
+    PREPARE TRANSACTION 'newgid';
+	});
+
+# Wait for the subscriber to catchup
+$node_publisher->wait_for_catchup($appname_copy);
+
+# Make sure there are no prepared transactions on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT count(*) FROM pg_prepared_xacts;");
+is($result, qq(0), 'should be no prepared transactions on subscriber');
+
+# Now commit the insert and verify that it IS replicated
+$node_publisher->safe_psql('postgres', "COMMIT PREPARED 'newgid';");
+
+# Wait for the subscriber to catchup
+$node_publisher->wait_for_catchup($appname_copy);
+
+# Make sure that the committed transaction is replicated.
+$result =
+	$node_subscriber->safe_psql('postgres', "SELECT count(*) FROM tab_copy;");
+is($result, qq(3), 'replicated data in subscriber table');
+
+# Alter subscription two_phase to true
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy DISABLE");
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = true)");
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy ENABLE");
+
+# Wait for subscription startup
+$node_subscriber->wait_for_subscription_sync($node_publisher, $appname_copy);
+
+# Make sure that the two-phase is enabled on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT subtwophasestate FROM pg_subscription WHERE subname = 'tap_sub_copy';"
+);
+is($result, qq(e), 'two-phase should be enabled');
+
 $node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub_copy;");
 $node_publisher->safe_psql('postgres', "DROP PUBLICATION tap_pub_copy;");
 
@@ -374,8 +443,6 @@ $node_publisher->safe_psql('postgres', "DROP PUBLICATION tap_pub_copy;");
 # check all the cleanup
 ###############################
 
-$node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub");
-
 $result = $node_subscriber->safe_psql('postgres',
 	"SELECT count(*) FROM pg_subscription");
 is($result, qq(0), 'check subscription was dropped on subscriber');
-- 
2.43.0

From be161c6fcc17161b66f4d4b342b98f5b3de25ebf Mon Sep 17 00:00:00 2001
From: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Date: Wed, 17 Apr 2024 06:18:23 +0000
Subject: [PATCH v10 2/4] Alter slot option two_phase only when altering "true"
 to "false"
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Since the two_phase option is controlled by both the publisher (as a slot option)
and the subscriber (as a subscription option), the slot option must also be
modified.

Regarding the false->true case, the backend process alters the subtwophase to
LOGICALREP_TWOPHASE_STATE_PENDING once. After the subscription is enabled, a new
logical replication worker requests to change the two_phase option of its slot
from pending to true after the initial data synchronization is done. The code
path is the same as the case in which two_phase is initially set to true, so
there is no need to do something remarkable. However, for the true->false case,
the backend must connect to the publisher and expressly change the parameter
because the apply worker does not alter the option to false. The operation cannot
be rolled back, and altering the parameter from "true" to "false" within a
transaction is prohibited.
---
 doc/src/sgml/ref/alter_subscription.sgml      |  2 +-
 src/backend/commands/subscriptioncmds.c       | 42 ++++++--
 .../libpqwalreceiver/libpqwalreceiver.c       | 23 +++--
 src/include/replication/walreceiver.h         |  5 +-
 src/test/subscription/meson.build             |  1 +
 src/test/subscription/t/099_twophase_added.pl | 96 +++++++++++++++++++
 6 files changed, 153 insertions(+), 16 deletions(-)
 create mode 100644 src/test/subscription/t/099_twophase_added.pl

diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index 88e9a72147..0c2894a94e 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -70,7 +70,7 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
    <command>ALTER SUBSCRIPTION ... {SET|ADD|DROP} PUBLICATION ...</command>
    with <literal>refresh</literal> option as <literal>true</literal>,
    <command>ALTER SUBSCRIPTION ... SET (failover = on|off)</command> and
-   <command>ALTER SUBSCRIPTION ... SET (two_phase = on|off)</command>
+   <command>ALTER SUBSCRIPTION ... SET (two_phase = off)</command>
    cannot be executed inside a transaction block.
 
    These commands also cannot be executed when the subscription has
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index 90d967eb7c..d9abf687d1 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -1097,6 +1097,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 	Form_pg_subscription form;
 	bits32		supported_opts;
 	SubOpts		opts = {0};
+	bool		update_failover;
+	bool		update_two_phase;
 
 	rel = table_open(SubscriptionRelationId, RowExclusiveLock);
 
@@ -1186,10 +1188,24 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 								 errhint("Resolve these transactions and try again")));
 
 					/*
-					 * The changed two_phase option of the slot can't be rolled
-					 * back.
+					 * Altering the parameter from "true" to "false" within a
+					 * transaction is prohibited. Since the apply worker does
+					 * not alter the slot option to false, the backend must
+					 * connect to the publisher and expressly change the
+					 * parameter.
+					 *
+					 * There is no need to do something remarkable regarding
+					 * the "false" to "true" case; the backend process alters
+					 * subtwophase to LOGICALREP_TWOPHASE_STATE_PENDING once.
+					 * After the subscription is enabled, a new logical
+					 * replication worker requests to change the two_phase
+					 * option of its slot when the initial data synchronization
+					 * is done. The code path is the same as the case in which
+					 * two_phase is initially set to true.
 					 */
-					PreventInTransactionBlock(isTopLevel, "ALTER SUBSCRIPTION ... SET (two_phase)");
+					if (!opts.twophase)
+						PreventInTransactionBlock(isTopLevel,
+												  "ALTER SUBSCRIPTION ... SET (two_phase = false)");
 
 					/* Change system catalog acoordingly */
 					values[Anum_pg_subscription_subtwophasestate - 1] =
@@ -1547,14 +1563,24 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 	}
 
 	/*
-	 * Try to acquire the connection necessary for altering slot.
+	 * Check the need to alter the replication slot. Failover and two_phase
+	 * options are controlled by both the publisher (as a slot option) and the
+	 * subscriber (as a subscription option). The slot option must be altered
+	 * only when changing "true" to "false". The reason has already been
+	 * described in the ALTER_SUBSCRIPTION_OPTIONS section of this function.
+	 */
+	update_failover = replaces[Anum_pg_subscription_subfailover - 1];
+	update_two_phase = (replaces[Anum_pg_subscription_subtwophasestate - 1] &&
+						!opts.twophase);
+
+	/*
+	 * Try to acquire the connection necessary for altering slot, if needed.
 	 *
 	 * This has to be at the end because otherwise if there is an error while
 	 * doing the database operations we won't be able to rollback altered
 	 * slot.
 	 */
-	if (replaces[Anum_pg_subscription_subfailover - 1] ||
-		replaces[Anum_pg_subscription_subtwophasestate - 1])
+	if (update_failover || update_two_phase)
 	{
 		bool		must_use_password;
 		char	   *err;
@@ -1574,7 +1600,9 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 
 		PG_TRY();
 		{
-			walrcv_alter_slot(wrconn, sub->slotname, opts.failover, opts.twophase);
+			walrcv_alter_slot(wrconn, sub->slotname,
+							  update_failover ? &opts.failover : NULL,
+							  update_two_phase ? &opts.twophase : NULL);
 		}
 		PG_FINALLY();
 		{
diff --git a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
index 998bbd517a..ff013aa987 100644
--- a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
+++ b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
@@ -80,7 +80,7 @@ static char *libpqrcv_create_slot(WalReceiverConn *conn,
 								  CRSSnapshotAction snapshot_action,
 								  XLogRecPtr *lsn);
 static void libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-								bool failover, bool two_phase);
+								const bool *failover, const bool *two_phase);
 static pid_t libpqrcv_get_backend_pid(WalReceiverConn *conn);
 static WalRcvExecResult *libpqrcv_exec(WalReceiverConn *conn,
 									   const char *query,
@@ -1121,16 +1121,27 @@ libpqrcv_create_slot(WalReceiverConn *conn, const char *slotname,
  */
 static void
 libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-					bool failover, bool two_phase)
+					const bool *failover, const bool *two_phase)
 {
 	StringInfoData cmd;
 	PGresult   *res;
 
 	initStringInfo(&cmd);
-	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( FAILOVER %s, TWO_PHASE %s )",
-					 quote_identifier(slotname),
-					 failover ? "true" : "false",
-					 two_phase ? "true" : "false");
+	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( ",
+					 quote_identifier(slotname));
+
+	if (failover)
+		appendStringInfo(&cmd, "FAILOVER %s",
+						 *failover ? "true" : "false");
+
+	if (failover && two_phase)
+		appendStringInfo(&cmd, ", ");
+
+	if (two_phase)
+		appendStringInfo(&cmd, "TWO_PHASE %s",
+						 *two_phase ? "true" : "false");
+
+	appendStringInfoString(&cmd, " );");
 
 	res = libpqrcv_PQexec(conn->streamConn, cmd.data);
 	pfree(cmd.data);
diff --git a/src/include/replication/walreceiver.h b/src/include/replication/walreceiver.h
index 31fa1257ec..7ffa5a58b3 100644
--- a/src/include/replication/walreceiver.h
+++ b/src/include/replication/walreceiver.h
@@ -377,8 +377,9 @@ typedef char *(*walrcv_create_slot_fn) (WalReceiverConn *conn,
  */
 typedef void (*walrcv_alter_slot_fn) (WalReceiverConn *conn,
 									  const char *slotname,
-									  bool failover,
-									  bool two_phase);
+									  const bool *failover,
+									  const bool *two_phase);
+
 
 /*
  * walrcv_get_backend_pid_fn
diff --git a/src/test/subscription/meson.build b/src/test/subscription/meson.build
index c591cd7d61..b4bd522c3d 100644
--- a/src/test/subscription/meson.build
+++ b/src/test/subscription/meson.build
@@ -40,6 +40,7 @@ tests += {
       't/031_column_list.pl',
       't/032_subscribe_use_index.pl',
       't/033_run_as_table_owner.pl',
+      't/099_twophase_added.pl',
       't/100_bugs.pl',
     ],
   },
diff --git a/src/test/subscription/t/099_twophase_added.pl b/src/test/subscription/t/099_twophase_added.pl
new file mode 100644
index 0000000000..b7c97f8454
--- /dev/null
+++ b/src/test/subscription/t/099_twophase_added.pl
@@ -0,0 +1,96 @@
+# Copyright (c) 2024, PostgreSQL Global Development Group
+
+# Additional tests for altering two_phase option
+use strict;
+use warnings FATAL => 'all';
+use PostgreSQL::Test::Cluster;
+use PostgreSQL::Test::Utils;
+use Test::More;
+
+# Initialize publisher node
+my $node_publisher = PostgreSQL::Test::Cluster->new('publisher');
+$node_publisher->init(allows_streaming => 'logical');
+$node_publisher->append_conf('postgresql.conf',
+	qq(max_prepared_transactions = 10));
+$node_publisher->start;
+
+# Create subscriber node
+my $node_subscriber = PostgreSQL::Test::Cluster->new('subscriber');
+$node_subscriber->init;
+$node_subscriber->append_conf('postgresql.conf',
+	qq(max_prepared_transactions = 10
+	log_min_messages = debug1));
+$node_subscriber->start;
+
+# Define tables on both nodes
+$node_publisher->safe_psql('postgres',
+    "CREATE TABLE tab_full (a int PRIMARY KEY);");
+$node_subscriber->safe_psql('postgres',
+	"CREATE TABLE tab_full (a int PRIMARY KEY)");
+
+# Setup logical replication, with two_phase = "false"
+my $publisher_connstr = $node_publisher->connstr . ' dbname=postgres';
+$node_publisher->safe_psql('postgres',
+	"CREATE PUBLICATION pub FOR ALL TABLES");
+
+my $log_offset = -s $node_subscriber->logfile;
+
+$node_subscriber->safe_psql(
+	'postgres', "
+	CREATE SUBSCRIPTION regress_sub
+	CONNECTION '$publisher_connstr' PUBLICATION pub
+	WITH (two_phase = false, copy_data = false, failover = false)");
+
+# Verify the started worker recognized two_phase was disabled
+$node_subscriber->wait_for_log(
+	'logical replication apply worker for subscription "regress_sub" two_phase is DISABLED', $log_offset);
+
+#####################
+# Check the case that prepared transactions exist on the publisher node.
+#
+# Since the two_phase is "off", then normally, this PREPARE will do nothing
+# until the COMMIT PREPARED, but in this test, we toggle the two_phase to
+# "true" again before the COMMIT PREPARED happens.
+
+# Prepare a transaction to insert some tuples into the table
+$node_publisher->safe_psql(
+	'postgres', "
+	BEGIN;
+	INSERT INTO tab_full VALUES (generate_series(1, 5));
+	PREPARE TRANSACTION 'test_prepared_tab_full';");
+
+$node_publisher->wait_for_catchup('regress_sub');
+
+# Verify the prepared transaction is not yet replicated to the subscriber
+# because two_phase is set to "false".
+my $result = $node_subscriber->safe_psql('postgres',
+    "SELECT count(*) FROM pg_prepared_xacts;");
+is($result, q(0), "transaction is not prepared on subscriber");
+
+$log_offset = -s $node_subscriber->logfile;
+
+# Toggle the two_phase to "true" *before* the COMMIT PREPARED. Since we are the
+# special path for the case where both two_phase and failover are altered, it
+# is also set to "true".
+$node_subscriber->safe_psql(
+    'postgres', "
+    ALTER SUBSCRIPTION regress_sub DISABLE;
+    ALTER SUBSCRIPTION regress_sub SET (two_phase = true, failover = true);
+    ALTER SUBSCRIPTION regress_sub ENABLE;");
+
+# Verify the started worker recognized two_phase was enabled
+$node_subscriber->wait_for_log(
+	'logical replication apply worker for subscription "regress_sub" two_phase is ENABLED', $log_offset);
+
+# And do COMMIT PREPARED the prepared transaction
+$node_publisher->safe_psql('postgres',
+    "COMMIT PREPARED 'test_prepared_tab_full';");
+$node_publisher->wait_for_catchup('regress_sub');
+
+# Verify inserted tuples are replicated
+$result = $node_subscriber->safe_psql('postgres',
+    "SELECT count(*) FROM tab_full;");
+is($result, q(5),
+   "prepared transactions done before altering can be replicated");
+
+done_testing();
-- 
2.43.0

From d8c07a0bd72ffa32c8e2a553254d79bdc3fac9db Mon Sep 17 00:00:00 2001
From: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Date: Mon, 8 Apr 2024 12:39:12 +0000
Subject: [PATCH v10 3/4] Abort prepared transactions while altering two_phase
 to off

If we alter the two_phase parameter from "on" to "off" and there are prepared
transactions on the subscriber, they won't be resolved. To avoid this issue, we
allow the backend to abort all prepared transactions while altering the
subscription.
---
 doc/src/sgml/ref/alter_subscription.sgml      | 11 ++-
 src/backend/access/transam/twophase.c         | 17 ++---
 src/backend/commands/subscriptioncmds.c       | 69 +++++++++++--------
 src/include/access/twophase.h                 |  3 +-
 src/test/subscription/t/099_twophase_added.pl | 45 ++++++++++++
 5 files changed, 104 insertions(+), 41 deletions(-)

diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index 0c2894a94e..2c6502275a 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -233,8 +233,6 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>, and
       <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>.
       Only a superuser can set <literal>password_required = false</literal>.
-      The <literal>two_phase</literal> parameter can only be altered when the
-      subscription is disabled.
      </para>
 
      <para>
@@ -256,6 +254,15 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>
       option is enabled.
      </para>
+
+     <para>
+      The <literal>two_phase</literal> parameter can only be altered when the
+      subscription is disabled. When altering the parameter from <literal>true</literal>
+      to <literal>false</literal>, the backend process checks for any incomplete
+      prepared transactions done by the logical replication worker (from when
+      <literal>two_phase</literal> parameter was still <literal>true</literal>)
+      and, if any are found, those are aborted.
+     </para>
     </listitem>
    </varlistentry>
 
diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index 66fa591eb5..f384bd8c0a 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -2720,13 +2720,13 @@ IsTwoPhaseTransactionGidForSubid(Oid subid, char *gid)
 }
 
 /*
- * LookupGXactBySubid
- *		Check if the prepared transaction done by apply worker exists.
+ * GetGidListBySubid
+ *      Get a list of GIDs which is PREPARE'd by the given subscription.
  */
-bool
-LookupGXactBySubid(Oid subid)
+List *
+GetGidListBySubid(Oid subid)
 {
-	bool		found = false;
+	List *list = NIL;
 
 	LWLockAcquire(TwoPhaseStateLock, LW_SHARED);
 	for (int i = 0; i < TwoPhaseState->numPrepXacts; i++)
@@ -2736,11 +2736,8 @@ LookupGXactBySubid(Oid subid)
 		/* Ignore not-yet-valid GIDs. */
 		if (gxact->valid &&
 			IsTwoPhaseTransactionGidForSubid(subid, gxact->gid))
-		{
-			found = true;
-			break;
-		}
+			list = lappend(list, pstrdup(gxact->gid));
 	}
 	LWLockRelease(TwoPhaseStateLock);
-	return found;
+	return list;
 }
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index d9abf687d1..c0e5d1af45 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -1176,36 +1176,49 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 					logicalrep_workers_stop(subid);
 
 					/*
-					 * two_phase cannot be disabled if there are any
-					 * uncommitted prepared transactions present.
-					 */
-					if (!opts.twophase &&
-						form->subtwophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
-						LookupGXactBySubid(subid))
-						ereport(ERROR,
-								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-								 errmsg("cannot disable two_phase when uncommitted prepared transactions present"),
-								 errhint("Resolve these transactions and try again")));
-
-					/*
-					 * Altering the parameter from "true" to "false" within a
-					 * transaction is prohibited. Since the apply worker does
-					 * not alter the slot option to false, the backend must
-					 * connect to the publisher and expressly change the
-					 * parameter.
-					 *
-					 * There is no need to do something remarkable regarding
-					 * the "false" to "true" case; the backend process alters
-					 * subtwophase to LOGICALREP_TWOPHASE_STATE_PENDING once.
-					 * After the subscription is enabled, a new logical
-					 * replication worker requests to change the two_phase
-					 * option of its slot when the initial data synchronization
-					 * is done. The code path is the same as the case in which
-					 * two_phase is initially set to true.
+					 * If two_phase was enabled, there is a possibility that
+					 * transactions have already been PREPARE'd. They must be
+					 * checked and rolled back.
 					 */
 					if (!opts.twophase)
-						PreventInTransactionBlock(isTopLevel,
-												  "ALTER SUBSCRIPTION ... SET (two_phase = false)");
+					{
+						List *prepared_xacts;
+
+						/*
+						 * Altering the parameter from "true" to "false" within
+						 * a transaction is prohibited. Since the apply worker
+						 * does not alter the slot option to false, the backend
+						 * must connect to the publisher and expressly change
+						 * the parameter.
+						 *
+						 * There is no need to do something remarkable
+						 * regarding the "false" to "true" case; the backend
+						 * process alters subtwophase to
+						 * LOGICALREP_TWOPHASE_STATE_PENDING once. After the
+						 * subscription is enabled, a new logical replication
+						 * worker requests to change the two_phase option of
+						 * its slot when the initial data synchronization is
+						 * done. The code path is the same as the case in which
+						 * two_phase is initially set to true.
+						 */
+						if (!opts.twophase)
+							PreventInTransactionBlock(isTopLevel,
+													"ALTER SUBSCRIPTION ... SET (two_phase = false)");
+
+						/*
+						 * To prevent prepared transactions from being
+						 * isolated, they must manually be aborted.
+						 */
+						if (sub->twophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
+							(prepared_xacts = GetGidListBySubid(subid)) != NIL)
+						{
+							/* Abort all listed transactions */
+							foreach_ptr(char, gid, prepared_xacts)
+								FinishPreparedTransaction(gid, false);
+
+							list_free_deep(prepared_xacts);
+						}
+					}
 
 					/* Change system catalog acoordingly */
 					values[Anum_pg_subscription_subtwophasestate - 1] =
diff --git a/src/include/access/twophase.h b/src/include/access/twophase.h
index d37e06fdee..f7a5cf0c12 100644
--- a/src/include/access/twophase.h
+++ b/src/include/access/twophase.h
@@ -18,6 +18,7 @@
 #include "access/xlogdefs.h"
 #include "datatype/timestamp.h"
 #include "storage/lock.h"
+#include "nodes/pg_list.h"
 
 /*
  * GlobalTransactionData is defined in twophase.c; other places have no
@@ -65,6 +66,6 @@ extern bool LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 
 extern void TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid,
 								   int szgid);
-extern bool LookupGXactBySubid(Oid subid);
+extern List *GetGidListBySubid(Oid subid);
 
 #endif							/* TWOPHASE_H */
diff --git a/src/test/subscription/t/099_twophase_added.pl b/src/test/subscription/t/099_twophase_added.pl
index b7c97f8454..7abe1c37d5 100644
--- a/src/test/subscription/t/099_twophase_added.pl
+++ b/src/test/subscription/t/099_twophase_added.pl
@@ -93,4 +93,49 @@ $result = $node_subscriber->safe_psql('postgres',
 is($result, q(5),
    "prepared transactions done before altering can be replicated");
 
+#####################
+# Check the case that prepared transactions exist on the subscriber node
+#
+# If the two_phase is altering from "on" to "off" and there are prepared
+# transactions on the subscriber, they must be aborted. This test checks it.
+
+# Prepare a transaction to insert some tuples into the table
+$node_publisher->safe_psql(
+	'postgres', "
+	BEGIN;
+	INSERT INTO tab_full VALUES (generate_series(6, 10));
+	PREPARE TRANSACTION 'test_prepared_tab_full';");
+
+$node_publisher->wait_for_catchup('regress_sub');
+
+# Verify the prepared transaction has been replicated to the subscriber because
+# two_phase is set to "on".
+$result = $node_subscriber->safe_psql('postgres',
+    "SELECT count(*) FROM pg_prepared_xacts;");
+is($result, q(1), "transaction has been prepared on subscriber");
+
+# Toggle the two_phase to "off" before the COMMIT PREPARED
+$node_subscriber->safe_psql(
+    'postgres', "
+    ALTER SUBSCRIPTION regress_sub DISABLE;
+    ALTER SUBSCRIPTION regress_sub SET (two_phase = off);
+    ALTER SUBSCRIPTION regress_sub ENABLE;");
+
+# Verify any prepared transactions are aborted because two_phase is changed to
+# "off".
+$result = $node_subscriber->safe_psql('postgres',
+    "SELECT count(*) FROM pg_prepared_xacts;");
+is($result, q(0), "prepared transaction done by worker is aborted");
+
+# Do COMMIT PREPARED the prepared transaction
+$node_publisher->safe_psql( 'postgres',
+    "COMMIT PREPARED 'test_prepared_tab_full';");
+$node_publisher->wait_for_catchup('regress_sub');
+
+# Verify inserted tuples are replicated
+$result = $node_subscriber->safe_psql('postgres',
+    "SELECT count(10) FROM tab_full;");
+is($result, q(10),
+   "prepared transactions on publisher can be replicated");
+
 done_testing();
-- 
2.43.0

From f2855efa1ccb7dfba197df652d9147b52c8a8270 Mon Sep 17 00:00:00 2001
From: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Date: Fri, 19 Apr 2024 11:03:19 +0000
Subject: [PATCH v10 4/4] Add force_alter option for ALTER SUBSCRIPTION ... SET
 command

Previously, all prepared transactions on the standby were rolled back when
toggling two_phase from "true" to "false". However, this operation may not be
expected by users. To ensure users understand what happens, we added the
"force_alter" parameter. When two_phase is toggling to "false", and there are
prepared transactions, they will be aborted only when "force_alter" is set to
true. Otherwise, an ERROR occurs.
---
 doc/src/sgml/catalogs.sgml                    |  12 ++
 doc/src/sgml/ref/alter_subscription.sgml      |  16 +-
 doc/src/sgml/ref/create_subscription.sgml     |  20 +++
 src/backend/catalog/pg_subscription.c         |   1 +
 src/backend/catalog/system_views.sql          |   2 +-
 src/backend/commands/subscriptioncmds.c       |  36 ++++-
 src/bin/pg_dump/pg_dump.c                     |  14 ++
 src/bin/pg_dump/pg_dump.h                     |   1 +
 src/bin/psql/describe.c                       |   7 +-
 src/include/catalog/pg_subscription.h         |  13 ++
 src/test/regress/expected/subscription.out    | 152 +++++++++---------
 src/test/subscription/t/099_twophase_added.pl |  43 +++--
 12 files changed, 221 insertions(+), 96 deletions(-)

diff --git a/doc/src/sgml/catalogs.sgml b/doc/src/sgml/catalogs.sgml
index 5a6f65025b..124982b0a2 100644
--- a/doc/src/sgml/catalogs.sgml
+++ b/doc/src/sgml/catalogs.sgml
@@ -8049,6 +8049,18 @@ SCRAM-SHA-256$<replaceable>&lt;iteration count&gt;</replaceable>:<replaceable>&l
       </para></entry>
      </row>
 
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>subforcealter</structfield> <type>bool</type>
+      </para>
+      <para>
+       If true, then the <link linkend="sql-altersubscription"><command>ALTER SUBSCRIPTION</command>
+       can disable <literal>two_phase</literal> option, even if there are
+       uncommitted prepared transactions from when <literal>two_phase</literal>
+       was enabled
+      </para></entry>
+     </row>
+
      <row>
       <entry role="catalog_table_entry"><para role="column_definition">
        <structfield>subconninfo</structfield> <type>text</type>
diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index 2c6502275a..e462d8c4d2 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -230,8 +230,9 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-password-required"><literal>password_required</literal></link>,
       <link linkend="sql-createsubscription-params-with-run-as-owner"><literal>run_as_owner</literal></link>,
       <link linkend="sql-createsubscription-params-with-origin"><literal>origin</literal></link>,
-      <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>, and
-      <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>.
+      <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>,
+      <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>, and
+      <link linkend="sql-createsubscription-params-with-force-alter"><literal>force_alter</literal></link>
       Only a superuser can set <literal>password_required = false</literal>.
      </para>
 
@@ -257,11 +258,12 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
 
      <para>
       The <literal>two_phase</literal> parameter can only be altered when the
-      subscription is disabled. When altering the parameter from <literal>true</literal>
-      to <literal>false</literal>, the backend process checks for any incomplete
-      prepared transactions done by the logical replication worker (from when
-      <literal>two_phase</literal> parameter was still <literal>true</literal>)
-      and, if any are found, those are aborted.
+      subscription is disabled. Altering the parameter from <literal>true</literal>
+      to <literal>false</literal> will give an error when when there are
+      prepared transactions done by the logical replication worker. If you want
+      to alter the parameter forcibly in this case,
+      <link linkend="sql-createsubscription-params-with-force-alter"><literal>force_alter</literal></link>
+      option must be set to <literal>true</literal> at the same time.
      </para>
     </listitem>
    </varlistentry>
diff --git a/doc/src/sgml/ref/create_subscription.sgml b/doc/src/sgml/ref/create_subscription.sgml
index 740b7d9421..e8ef965c81 100644
--- a/doc/src/sgml/ref/create_subscription.sgml
+++ b/doc/src/sgml/ref/create_subscription.sgml
@@ -428,6 +428,26 @@ CREATE SUBSCRIPTION <replaceable class="parameter">subscription_name</replaceabl
          </para>
         </listitem>
        </varlistentry>
+
+       <varlistentry id="sql-createsubscription-params-with-force-alter">
+        <term><literal>force_alter</literal> (<type>boolean</type>)</term>
+        <listitem>
+         <para>
+          Specifies if the <link linkend="sql-altersubscription"><command>ALTER SUBSCRIPTION</command>
+          can be forced to proceed instead of giving an error. There is
+          currently only one scenario where this parameter has any effect: When
+          altering <literal>two_phase</literal> option from <literal>true</literal>
+          to <literal>false</literal> it is possible for there to be incomplete
+          prepared transactions done by the logical replication worker (from
+          when <literal>two_phase</literal> parameter was still <literal>true</literal>).
+          If <literal>force_alter</literal> is <literal>false</literal>, then
+          this will give an error; if <literal>force_alter</literal> is
+          <literal>true</literal>, then the incomplete prepared transactions
+          are aborted and the alter will proceed.
+          The default is <literal>false</literal>.
+         </para>
+        </listitem>
+       </varlistentry>
       </variablelist></para>
 
     </listitem>
diff --git a/src/backend/catalog/pg_subscription.c b/src/backend/catalog/pg_subscription.c
index 9efc9159f2..b568fe3470 100644
--- a/src/backend/catalog/pg_subscription.c
+++ b/src/backend/catalog/pg_subscription.c
@@ -72,6 +72,7 @@ GetSubscription(Oid subid, bool missing_ok)
 	sub->passwordrequired = subform->subpasswordrequired;
 	sub->runasowner = subform->subrunasowner;
 	sub->failover = subform->subfailover;
+	sub->forcealter = subform->subforcealter;
 
 	/* Get conninfo */
 	datum = SysCacheGetAttrNotNull(SUBSCRIPTIONOID,
diff --git a/src/backend/catalog/system_views.sql b/src/backend/catalog/system_views.sql
index 53047cab5f..de3d3d8f3e 100644
--- a/src/backend/catalog/system_views.sql
+++ b/src/backend/catalog/system_views.sql
@@ -1358,7 +1358,7 @@ REVOKE ALL ON pg_replication_origin_status FROM public;
 REVOKE ALL ON pg_subscription FROM public;
 GRANT SELECT (oid, subdbid, subskiplsn, subname, subowner, subenabled,
               subbinary, substream, subtwophasestate, subdisableonerr,
-			  subpasswordrequired, subrunasowner, subfailover,
+			  subpasswordrequired, subrunasowner, subfailover, subforcealter,
               subslotname, subsynccommit, subpublications, suborigin)
     ON pg_subscription TO public;
 
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index c0e5d1af45..32d00d2c2a 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -73,6 +73,7 @@
 #define SUBOPT_FAILOVER				0x00002000
 #define SUBOPT_LSN					0x00004000
 #define SUBOPT_ORIGIN				0x00008000
+#define SUBOPT_FORCE_ALTER			0x00010000
 
 /* check if the 'val' has 'bits' set */
 #define IsSet(val, bits)  (((val) & (bits)) == (bits))
@@ -100,6 +101,7 @@ typedef struct SubOpts
 	bool		failover;
 	char	   *origin;
 	XLogRecPtr	lsn;
+	bool		force_alter;
 } SubOpts;
 
 static List *fetch_table_list(WalReceiverConn *wrconn, List *publications);
@@ -162,6 +164,8 @@ parse_subscription_options(ParseState *pstate, List *stmt_options,
 		opts->failover = false;
 	if (IsSet(supported_opts, SUBOPT_ORIGIN))
 		opts->origin = pstrdup(LOGICALREP_ORIGIN_ANY);
+	if (IsSet(supported_opts, SUBOPT_FORCE_ALTER))
+		opts->force_alter = false;
 
 	/* Parse options */
 	foreach(lc, stmt_options)
@@ -367,6 +371,15 @@ parse_subscription_options(ParseState *pstate, List *stmt_options,
 			opts->specified_opts |= SUBOPT_LSN;
 			opts->lsn = lsn;
 		}
+		else if (IsSet(supported_opts, SUBOPT_FORCE_ALTER) &&
+				 strcmp(defel->defname, "force_alter") == 0)
+		{
+			if (IsSet(opts->specified_opts, SUBOPT_FORCE_ALTER))
+				errorConflictingDefElem(defel, pstate);
+
+			opts->specified_opts |= SUBOPT_FORCE_ALTER;
+			opts->force_alter = defGetBoolean(defel);
+		}
 		else
 			ereport(ERROR,
 					(errcode(ERRCODE_SYNTAX_ERROR),
@@ -604,7 +617,8 @@ CreateSubscription(ParseState *pstate, CreateSubscriptionStmt *stmt,
 					  SUBOPT_SYNCHRONOUS_COMMIT | SUBOPT_BINARY |
 					  SUBOPT_STREAMING | SUBOPT_TWOPHASE_COMMIT |
 					  SUBOPT_DISABLE_ON_ERR | SUBOPT_PASSWORD_REQUIRED |
-					  SUBOPT_RUN_AS_OWNER | SUBOPT_FAILOVER | SUBOPT_ORIGIN);
+					  SUBOPT_RUN_AS_OWNER | SUBOPT_FAILOVER | SUBOPT_ORIGIN |
+					  SUBOPT_FORCE_ALTER);
 	parse_subscription_options(pstate, stmt->options, supported_opts, &opts);
 
 	/*
@@ -711,6 +725,7 @@ CreateSubscription(ParseState *pstate, CreateSubscriptionStmt *stmt,
 	values[Anum_pg_subscription_subpasswordrequired - 1] = BoolGetDatum(opts.passwordrequired);
 	values[Anum_pg_subscription_subrunasowner - 1] = BoolGetDatum(opts.runasowner);
 	values[Anum_pg_subscription_subfailover - 1] = BoolGetDatum(opts.failover);
+	values[Anum_pg_subscription_subforcealter - 1] = BoolGetDatum(opts.force_alter);
 	values[Anum_pg_subscription_subconninfo - 1] =
 		CStringGetTextDatum(conninfo);
 	if (opts.slot_name)
@@ -1150,7 +1165,7 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 								  SUBOPT_DISABLE_ON_ERR |
 								  SUBOPT_PASSWORD_REQUIRED |
 								  SUBOPT_RUN_AS_OWNER | SUBOPT_FAILOVER |
-								  SUBOPT_ORIGIN);
+								  SUBOPT_ORIGIN | SUBOPT_FORCE_ALTER);
 
 				parse_subscription_options(pstate, stmt->options,
 										   supported_opts, &opts);
@@ -1212,6 +1227,23 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 						if (sub->twophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
 							(prepared_xacts = GetGidListBySubid(subid)) != NIL)
 						{
+							bool raise_error =
+								IsSet(opts.specified_opts, SUBOPT_FORCE_ALTER) ?
+									!opts.force_alter : !sub->forcealter;
+
+							/*
+							 * Abort prepared transactions only if
+							 * 'force_alter' option is true. Otherwise raise
+							 * an ERROR.
+							 */
+							if (raise_error)
+								ereport(ERROR,
+										(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+										 errmsg("cannot alter %s when there are prepared transactions",
+												"two_phase = false"),
+										 errhint("Resolve these transactions or set %s, and then try again.",
+												 "force_alter = true")));
+
 							/* Abort all listed transactions */
 							foreach_ptr(char, gid, prepared_xacts)
 								FinishPreparedTransaction(gid, false);
diff --git a/src/bin/pg_dump/pg_dump.c b/src/bin/pg_dump/pg_dump.c
index ac920f64c7..b4b0c9e583 100644
--- a/src/bin/pg_dump/pg_dump.c
+++ b/src/bin/pg_dump/pg_dump.c
@@ -4739,6 +4739,7 @@ getSubscriptions(Archive *fout)
 	int			i_suboriginremotelsn;
 	int			i_subenabled;
 	int			i_subfailover;
+	int			i_subforcealter;
 	int			i,
 				ntups;
 
@@ -4816,6 +4817,13 @@ getSubscriptions(Archive *fout)
 		appendPQExpBuffer(query,
 						  " false AS subfailover\n");
 
+	if (fout->remoteVersion >= 170000)
+		appendPQExpBufferStr(query,
+							 " s.subforcealter\n");
+	else
+		appendPQExpBuffer(query,
+						  " false AS subforcealter\n");
+
 	appendPQExpBufferStr(query,
 						 "FROM pg_subscription s\n");
 
@@ -4854,6 +4862,7 @@ getSubscriptions(Archive *fout)
 	i_suboriginremotelsn = PQfnumber(res, "suboriginremotelsn");
 	i_subenabled = PQfnumber(res, "subenabled");
 	i_subfailover = PQfnumber(res, "subfailover");
+	i_subforcealter = PQfnumber(res, "subforcealter");
 
 	subinfo = pg_malloc(ntups * sizeof(SubscriptionInfo));
 
@@ -4900,6 +4909,8 @@ getSubscriptions(Archive *fout)
 			pg_strdup(PQgetvalue(res, i, i_subenabled));
 		subinfo[i].subfailover =
 			pg_strdup(PQgetvalue(res, i, i_subfailover));
+		subinfo[i].subforcealter =
+			pg_strdup(PQgetvalue(res, i, i_subforcealter));
 
 		/* Decide whether we want to dump it */
 		selectDumpableObject(&(subinfo[i].dobj), fout);
@@ -5140,6 +5151,9 @@ dumpSubscription(Archive *fout, const SubscriptionInfo *subinfo)
 	if (strcmp(subinfo->subfailover, "t") == 0)
 		appendPQExpBufferStr(query, ", failover = true");
 
+	if (strcmp(subinfo->subforcealter, "t") == 0)
+		appendPQExpBufferStr(query, ", force_alter = true");
+
 	if (strcmp(subinfo->subsynccommit, "off") != 0)
 		appendPQExpBuffer(query, ", synchronous_commit = %s", fmtId(subinfo->subsynccommit));
 
diff --git a/src/bin/pg_dump/pg_dump.h b/src/bin/pg_dump/pg_dump.h
index f518a1e6d2..c666b9c113 100644
--- a/src/bin/pg_dump/pg_dump.h
+++ b/src/bin/pg_dump/pg_dump.h
@@ -672,6 +672,7 @@ typedef struct _SubscriptionInfo
 	char	   *suborigin;
 	char	   *suboriginremotelsn;
 	char	   *subfailover;
+	char	   *subforcealter;
 } SubscriptionInfo;
 
 /*
diff --git a/src/bin/psql/describe.c b/src/bin/psql/describe.c
index 3af44acef1..8e0a0b3b36 100644
--- a/src/bin/psql/describe.c
+++ b/src/bin/psql/describe.c
@@ -6537,7 +6537,7 @@ describeSubscriptions(const char *pattern, bool verbose)
 	printQueryOpt myopt = pset.popt;
 	static const bool translate_columns[] = {false, false, false, false,
 		false, false, false, false, false, false, false, false, false, false,
-	false};
+	false, false};
 
 	if (pset.sversion < 100000)
 	{
@@ -6606,6 +6606,11 @@ describeSubscriptions(const char *pattern, bool verbose)
 							  ", subfailover AS \"%s\"\n",
 							  gettext_noop("Failover"));
 
+		if (pset.sversion >= 170000)
+			appendPQExpBuffer(&buf,
+							  ", subforcealter AS \"%s\"\n",
+							  gettext_noop("Force alter"));
+
 		appendPQExpBuffer(&buf,
 						  ",  subsynccommit AS \"%s\"\n"
 						  ",  subconninfo AS \"%s\"\n",
diff --git a/src/include/catalog/pg_subscription.h b/src/include/catalog/pg_subscription.h
index 0aa14ec4a2..c23de43d79 100644
--- a/src/include/catalog/pg_subscription.h
+++ b/src/include/catalog/pg_subscription.h
@@ -98,6 +98,13 @@ CATALOG(pg_subscription,6100,SubscriptionRelationId) BKI_SHARED_RELATION BKI_ROW
 								 * slots) in the upstream database are enabled
 								 * to be synchronized to the standbys. */
 
+	bool		subforcealter;	/* True allows the ALTER SUBSCRIPTION command
+								 * to proceed under conditions that would
+								 * otherwise result in an error. Currently,
+								 * 'force_alter' only has an effect when
+								 * altering the two_phase option from "true" to
+								 * "false". */
+
 #ifdef CATALOG_VARLEN			/* variable-length fields start here */
 	/* Connection string to the publisher */
 	text		subconninfo BKI_FORCE_NOT_NULL;
@@ -151,6 +158,12 @@ typedef struct Subscription
 								 * (i.e. the main slot and the table sync
 								 * slots) in the upstream database are enabled
 								 * to be synchronized to the standbys. */
+	bool		forcealter;		/* True allows the ALTER SUBSCRIPTION command
+								 * to proceed under conditions that would
+								 * otherwise result in an error. Currently,
+								 * 'force_alter' only has an effect when
+								 * altering the two_phase option from "true" to
+								 * "false". */
 	char	   *conninfo;		/* Connection string to the publisher */
 	char	   *slotname;		/* Name of the replication slot */
 	char	   *synccommit;		/* Synchronous commit setting for worker */
diff --git a/src/test/regress/expected/subscription.out b/src/test/regress/expected/subscription.out
index 51fa4b9690..b36fc6b8f7 100644
--- a/src/test/regress/expected/subscription.out
+++ b/src/test/regress/expected/subscription.out
@@ -116,18 +116,18 @@ CREATE SUBSCRIPTION regress_testsub4 CONNECTION 'dbname=regress_doesnotexist' PU
 WARNING:  subscription was created, but is not connected
 HINT:  To initiate replication, you must manually create the replication slot, enable the subscription, and refresh the subscription.
 \dRs+ regress_testsub4
-                                                                                                                 List of subscriptions
-       Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
-------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub4 | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | none   | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                        List of subscriptions
+       Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub4 | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | none   | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub4 SET (origin = any);
 \dRs+ regress_testsub4
-                                                                                                                 List of subscriptions
-       Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
-------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub4 | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                        List of subscriptions
+       Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub4 | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 DROP SUBSCRIPTION regress_testsub3;
@@ -145,10 +145,10 @@ ALTER SUBSCRIPTION regress_testsub CONNECTION 'foobar';
 ERROR:  invalid connection string syntax: missing "=" after "foobar" in connection info string
 
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET PUBLICATION testpub2, testpub3 WITH (refresh = false);
@@ -157,10 +157,10 @@ ALTER SUBSCRIPTION regress_testsub SET (slot_name = 'newname');
 ALTER SUBSCRIPTION regress_testsub SET (password_required = false);
 ALTER SUBSCRIPTION regress_testsub SET (run_as_owner = true);
 \dRs+
-                                                                                                                     List of subscriptions
-      Name       |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |           Conninfo           | Skip LSN 
------------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+------------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | f                 | t             | f        | off                | dbname=regress_doesnotexist2 | 0/0
+                                                                                                                            List of subscriptions
+      Name       |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |           Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+------------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | f                 | t             | f        | f           | off                | dbname=regress_doesnotexist2 | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (password_required = true);
@@ -176,10 +176,10 @@ ERROR:  unrecognized subscription parameter: "create_slot"
 -- ok
 ALTER SUBSCRIPTION regress_testsub SKIP (lsn = '0/12345');
 \dRs+
-                                                                                                                     List of subscriptions
-      Name       |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |           Conninfo           | Skip LSN 
------------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+------------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist2 | 0/12345
+                                                                                                                            List of subscriptions
+      Name       |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |           Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+------------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist2 | 0/12345
 (1 row)
 
 -- ok - with lsn = NONE
@@ -188,10 +188,10 @@ ALTER SUBSCRIPTION regress_testsub SKIP (lsn = NONE);
 ALTER SUBSCRIPTION regress_testsub SKIP (lsn = '0/0');
 ERROR:  invalid WAL location (LSN): 0/0
 \dRs+
-                                                                                                                     List of subscriptions
-      Name       |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |           Conninfo           | Skip LSN 
------------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+------------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist2 | 0/0
+                                                                                                                            List of subscriptions
+      Name       |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |           Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+------------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist2 | 0/0
 (1 row)
 
 BEGIN;
@@ -223,10 +223,10 @@ ALTER SUBSCRIPTION regress_testsub_foo SET (synchronous_commit = foobar);
 ERROR:  invalid value for parameter "synchronous_commit": "foobar"
 HINT:  Available values: local, remote_write, remote_apply, on, off.
 \dRs+
-                                                                                                                       List of subscriptions
-        Name         |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |           Conninfo           | Skip LSN 
----------------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+------------------------------+----------
- regress_testsub_foo | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | t                 | f             | f        | local              | dbname=regress_doesnotexist2 | 0/0
+                                                                                                                              List of subscriptions
+        Name         |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |           Conninfo           | Skip LSN 
+---------------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+------------------------------+----------
+ regress_testsub_foo | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | t                 | f             | f        | f           | local              | dbname=regress_doesnotexist2 | 0/0
 (1 row)
 
 -- rename back to keep the rest simple
@@ -255,19 +255,19 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 WARNING:  subscription was created, but is not connected
 HINT:  To initiate replication, you must manually create the replication slot, enable the subscription, and refresh the subscription.
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | t      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | t      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (binary = false);
 ALTER SUBSCRIPTION regress_testsub SET (slot_name = NONE);
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 DROP SUBSCRIPTION regress_testsub;
@@ -279,27 +279,27 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 WARNING:  subscription was created, but is not connected
 HINT:  To initiate replication, you must manually create the replication slot, enable the subscription, and refresh the subscription.
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | on        | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | on        | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (streaming = parallel);
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | parallel  | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | parallel  | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (streaming = false);
 ALTER SUBSCRIPTION regress_testsub SET (slot_name = NONE);
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 -- fail - publication already exists
@@ -314,10 +314,10 @@ ALTER SUBSCRIPTION regress_testsub ADD PUBLICATION testpub1, testpub2 WITH (refr
 ALTER SUBSCRIPTION regress_testsub ADD PUBLICATION testpub1, testpub2 WITH (refresh = false);
 ERROR:  publication "testpub1" is already in subscription "regress_testsub"
 \dRs+
-                                                                                                                        List of subscriptions
-      Name       |           Owner           | Enabled |         Publication         | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-----------------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub,testpub1,testpub2} | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                               List of subscriptions
+      Name       |           Owner           | Enabled |         Publication         | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-----------------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub,testpub1,testpub2} | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 -- fail - publication used more than once
@@ -332,10 +332,10 @@ ERROR:  publication "testpub3" is not in subscription "regress_testsub"
 -- ok - delete publications
 ALTER SUBSCRIPTION regress_testsub DROP PUBLICATION testpub1, testpub2 WITH (refresh = false);
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 DROP SUBSCRIPTION regress_testsub;
@@ -371,19 +371,19 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 WARNING:  subscription was created, but is not connected
 HINT:  To initiate replication, you must manually create the replication slot, enable the subscription, and refresh the subscription.
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | p                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | p                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 -- We can alter streaming when two_phase enabled
 ALTER SUBSCRIPTION regress_testsub SET (streaming = true);
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | on        | p                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | on        | p                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (slot_name = NONE);
@@ -393,10 +393,10 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 WARNING:  subscription was created, but is not connected
 HINT:  To initiate replication, you must manually create the replication slot, enable the subscription, and refresh the subscription.
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | on        | p                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | on        | p                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (slot_name = NONE);
@@ -409,18 +409,18 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 WARNING:  subscription was created, but is not connected
 HINT:  To initiate replication, you must manually create the replication slot, enable the subscription, and refresh the subscription.
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (disable_on_error = true);
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | t                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | t                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (slot_name = NONE);
diff --git a/src/test/subscription/t/099_twophase_added.pl b/src/test/subscription/t/099_twophase_added.pl
index 7abe1c37d5..188a3fa7a3 100644
--- a/src/test/subscription/t/099_twophase_added.pl
+++ b/src/test/subscription/t/099_twophase_added.pl
@@ -97,7 +97,8 @@ is($result, q(5),
 # Check the case that prepared transactions exist on the subscriber node
 #
 # If the two_phase is altering from "on" to "off" and there are prepared
-# transactions on the subscriber, they must be aborted. This test checks it.
+# transactions on the subscriber, we must error out or abort all prepared
+# transactions. Below part checks both cases.
 
 # Prepare a transaction to insert some tuples into the table
 $node_publisher->safe_psql(
@@ -114,15 +115,39 @@ $result = $node_subscriber->safe_psql('postgres',
     "SELECT count(*) FROM pg_prepared_xacts;");
 is($result, q(1), "transaction has been prepared on subscriber");
 
-# Toggle the two_phase to "off" before the COMMIT PREPARED
-$node_subscriber->safe_psql(
-    'postgres', "
-    ALTER SUBSCRIPTION regress_sub DISABLE;
-    ALTER SUBSCRIPTION regress_sub SET (two_phase = off);
-    ALTER SUBSCRIPTION regress_sub ENABLE;");
+# Disable the subscription to alter the two_phase option
+$node_subscriber->safe_psql('postgres', "ALTER SUBSCRIPTION regress_sub DISABLE;");
+
+# Try altering the two_phase option to "off." The command will fail since there
+# is a prepared transaction and the 'force_alter' option is not specified as
+# true.
+my $stdout;
+my $stderr;
+
+($result, $stdout, $stderr) = $node_subscriber->psql(
+	'postgres', "ALTER SUBSCRIPTION regress_sub SET (two_phase = false);");
+ok($stderr =~ /cannot alter two_phase = false when there are prepared transactions/,
+	'ALTER SUBSCRIPTION failed');
+
+# Verify the prepared transaction still exists
+$result = $node_subscriber->safe_psql('postgres',
+    "SELECT count(*) FROM pg_prepared_xacts;");
+is($result, q(1), "prepared transaction still exists");
+
+$log_offset = -s $node_subscriber->logfile;
+
+# Alter the two_phase with the force_alter option. Apart from the the last
+# ALTER SUBSCRIPTION command, the command will abort the prepared transaction
+# and succeed.
+$node_subscriber->safe_psql('postgres',
+    "ALTER SUBSCRIPTION regress_sub SET (two_phase = off, force_alter = true);");
+$node_subscriber->safe_psql('postgres', "ALTER SUBSCRIPTION regress_sub ENABLE;");
+
+# Verify the started worker recognized two_phase was disabled
+$node_subscriber->wait_for_log(
+	'logical replication apply worker for subscription "regress_sub" two_phase is DISABLED', $log_offset);
 
-# Verify any prepared transactions are aborted because two_phase is changed to
-# "off".
+# Verify the prepared transaction was aborted
 $result = $node_subscriber->safe_psql('postgres',
     "SELECT count(*) FROM pg_prepared_xacts;");
 is($result, q(0), "prepared transaction done by worker is aborted");
-- 
2.43.0

From bd3ff2c6e88a7dd5578cfd266848b824c1ff8546 Mon Sep 17 00:00:00 2001
From: Ajin Cherian <ajinc@fast.au.fujitsu.com>
Date: Fri, 5 Apr 2024 06:47:18 -0400
Subject: [PATCH v11 1/4] Allow altering of two_phase option of a SUBSCRIPTION

This patch allows the user to alter the 'two_phase' option of a subscriber provided no
uncommitted prepared transactions are pending on that subscription.

Author: Cherian Ajin, Hayato Kuroda
---
 doc/src/sgml/ref/alter_subscription.sgml      | 12 ++--
 src/backend/access/transam/twophase.c         | 62 ++++++++++++++++
 src/backend/commands/subscriptioncmds.c       | 67 +++++++++++++----
 .../libpqwalreceiver/libpqwalreceiver.c       |  9 +--
 src/backend/replication/logical/launcher.c    | 22 ++++++
 src/backend/replication/logical/worker.c      | 21 +-----
 src/backend/replication/slot.c                | 18 ++++-
 src/backend/replication/walsender.c           | 18 ++++-
 src/bin/psql/tab-complete.c                   |  2 +-
 src/include/access/twophase.h                 |  5 ++
 src/include/replication/slot.h                |  3 +-
 src/include/replication/walreceiver.h         | 11 +--
 src/include/replication/worker_internal.h     |  1 +
 src/test/regress/expected/subscription.out    |  5 +-
 src/test/regress/sql/subscription.sql         |  5 +-
 src/test/subscription/t/021_twophase.pl       | 71 ++++++++++++++++++-
 16 files changed, 269 insertions(+), 63 deletions(-)

diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index a78c1c3a47..88e9a72147 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -68,8 +68,9 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
   <para>
    Commands <command>ALTER SUBSCRIPTION ... REFRESH PUBLICATION</command>,
    <command>ALTER SUBSCRIPTION ... {SET|ADD|DROP} PUBLICATION ...</command>
-   with <literal>refresh</literal> option as <literal>true</literal> and
-   <command>ALTER SUBSCRIPTION ... SET (failover = on|off)</command>
+   with <literal>refresh</literal> option as <literal>true</literal>,
+   <command>ALTER SUBSCRIPTION ... SET (failover = on|off)</command> and
+   <command>ALTER SUBSCRIPTION ... SET (two_phase = on|off)</command>
    cannot be executed inside a transaction block.
 
    These commands also cannot be executed when the subscription has
@@ -228,9 +229,12 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-disable-on-error"><literal>disable_on_error</literal></link>,
       <link linkend="sql-createsubscription-params-with-password-required"><literal>password_required</literal></link>,
       <link linkend="sql-createsubscription-params-with-run-as-owner"><literal>run_as_owner</literal></link>,
-      <link linkend="sql-createsubscription-params-with-origin"><literal>origin</literal></link>, and
-      <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>.
+      <link linkend="sql-createsubscription-params-with-origin"><literal>origin</literal></link>,
+      <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>, and
+      <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>.
       Only a superuser can set <literal>password_required = false</literal>.
+      The <literal>two_phase</literal> parameter can only be altered when the
+      subscription is disabled.
      </para>
 
      <para>
diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index 8090ac9fc1..66fa591eb5 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -2682,3 +2682,65 @@ LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 	LWLockRelease(TwoPhaseStateLock);
 	return found;
 }
+
+/*
+ * TwoPhaseTransactionGid
+ *		Form the prepared transaction GID for two_phase transactions.
+ *
+ * Return the GID in the supplied buffer.
+ */
+void
+TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid, int szgid)
+{
+	Assert(subid != InvalidRepOriginId);
+
+	if (!TransactionIdIsValid(xid))
+		ereport(ERROR,
+				(errcode(ERRCODE_PROTOCOL_VIOLATION),
+				 errmsg_internal("invalid two-phase transaction ID")));
+
+	snprintf(gid, szgid, "pg_gid_%u_%u", subid, xid);
+}
+
+/*
+ * IsTwoPhaseTransactionGidForSubid
+ *		Check whether the given GID (as formed by TwoPhaseTransactionGid) is
+ *		for the specified 'subid'.
+ */
+static bool
+IsTwoPhaseTransactionGidForSubid(Oid subid, char *gid)
+{
+	int				ret;
+	Oid				subid_written;
+	TransactionId	xid;
+
+	ret = sscanf(gid, "pg_gid_%u_%u", &subid_written, &xid);
+
+	return (ret == 2 && subid == subid_written);
+}
+
+/*
+ * LookupGXactBySubid
+ *		Check if the prepared transaction done by apply worker exists.
+ */
+bool
+LookupGXactBySubid(Oid subid)
+{
+	bool		found = false;
+
+	LWLockAcquire(TwoPhaseStateLock, LW_SHARED);
+	for (int i = 0; i < TwoPhaseState->numPrepXacts; i++)
+	{
+		GlobalTransaction gxact = TwoPhaseState->prepXacts[i];
+
+		/* Ignore not-yet-valid GIDs. */
+		if (gxact->valid &&
+			IsTwoPhaseTransactionGidForSubid(subid, gxact->gid))
+		{
+			found = true;
+			break;
+		}
+	}
+	LWLockRelease(TwoPhaseStateLock);
+	return found;
+}
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index e407428dbc..90d967eb7c 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -16,6 +16,7 @@
 
 #include "access/htup_details.h"
 #include "access/table.h"
+#include "access/twophase.h"
 #include "access/xact.h"
 #include "catalog/catalog.h"
 #include "catalog/dependency.h"
@@ -1143,7 +1144,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 			{
 				supported_opts = (SUBOPT_SLOT_NAME |
 								  SUBOPT_SYNCHRONOUS_COMMIT | SUBOPT_BINARY |
-								  SUBOPT_STREAMING | SUBOPT_DISABLE_ON_ERR |
+								  SUBOPT_STREAMING | SUBOPT_TWOPHASE_COMMIT |
+								  SUBOPT_DISABLE_ON_ERR |
 								  SUBOPT_PASSWORD_REQUIRED |
 								  SUBOPT_RUN_AS_OWNER | SUBOPT_FAILOVER |
 								  SUBOPT_ORIGIN);
@@ -1151,6 +1153,52 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 				parse_subscription_options(pstate, stmt->options,
 										   supported_opts, &opts);
 
+				if (IsSet(opts.specified_opts, SUBOPT_TWOPHASE_COMMIT))
+				{
+					/*
+					 * Do not allow changing the two_phase option if the
+					 * subscription is enabled. This is because the two_phase
+					 * option of the slot on the publisher cannot be modified
+					 * if the slot is currently acquired by the apply worker.
+					 */
+					if (form->subenabled)
+						ereport(ERROR,
+								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+								 errmsg("cannot set %s for enabled subscription",
+										"two_phase")));
+
+					/*
+					 * Stop all the subscription workers, just in case. Workers
+					 * may still survive even if the subscription is disabled.
+					 */
+					logicalrep_workers_stop(subid);
+
+					/*
+					 * two_phase cannot be disabled if there are any
+					 * uncommitted prepared transactions present.
+					 */
+					if (!opts.twophase &&
+						form->subtwophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
+						LookupGXactBySubid(subid))
+						ereport(ERROR,
+								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+								 errmsg("cannot disable two_phase when uncommitted prepared transactions present"),
+								 errhint("Resolve these transactions and try again")));
+
+					/*
+					 * The changed two_phase option of the slot can't be rolled
+					 * back.
+					 */
+					PreventInTransactionBlock(isTopLevel, "ALTER SUBSCRIPTION ... SET (two_phase)");
+
+					/* Change system catalog acoordingly */
+					values[Anum_pg_subscription_subtwophasestate - 1] =
+						CharGetDatum(opts.twophase ?
+									 LOGICALREP_TWOPHASE_STATE_PENDING :
+									 LOGICALREP_TWOPHASE_STATE_DISABLED);
+					replaces[Anum_pg_subscription_subtwophasestate - 1] = true;
+				}
+
 				if (IsSet(opts.specified_opts, SUBOPT_SLOT_NAME))
 				{
 					/*
@@ -1505,7 +1553,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 	 * doing the database operations we won't be able to rollback altered
 	 * slot.
 	 */
-	if (replaces[Anum_pg_subscription_subfailover - 1])
+	if (replaces[Anum_pg_subscription_subfailover - 1] ||
+		replaces[Anum_pg_subscription_subtwophasestate - 1])
 	{
 		bool		must_use_password;
 		char	   *err;
@@ -1525,7 +1574,7 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 
 		PG_TRY();
 		{
-			walrcv_alter_slot(wrconn, sub->slotname, opts.failover);
+			walrcv_alter_slot(wrconn, sub->slotname, opts.failover, opts.twophase);
 		}
 		PG_FINALLY();
 		{
@@ -1562,7 +1611,6 @@ DropSubscription(DropSubscriptionStmt *stmt, bool isTopLevel)
 	char	   *subname;
 	char	   *conninfo;
 	char	   *slotname;
-	List	   *subworkers;
 	ListCell   *lc;
 	char		originname[NAMEDATALEN];
 	char	   *err = NULL;
@@ -1672,16 +1720,7 @@ DropSubscription(DropSubscriptionStmt *stmt, bool isTopLevel)
 	 * New workers won't be started because we hold an exclusive lock on the
 	 * subscription till the end of the transaction.
 	 */
-	LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
-	subworkers = logicalrep_workers_find(subid, false);
-	LWLockRelease(LogicalRepWorkerLock);
-	foreach(lc, subworkers)
-	{
-		LogicalRepWorker *w = (LogicalRepWorker *) lfirst(lc);
-
-		logicalrep_worker_stop(w->subid, w->relid);
-	}
-	list_free(subworkers);
+	logicalrep_workers_stop(subid);
 
 	/*
 	 * Remove the no-longer-useful entry in the launcher's table of apply
diff --git a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
index 3c2b1bb496..998bbd517a 100644
--- a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
+++ b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
@@ -80,7 +80,7 @@ static char *libpqrcv_create_slot(WalReceiverConn *conn,
 								  CRSSnapshotAction snapshot_action,
 								  XLogRecPtr *lsn);
 static void libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-								bool failover);
+								bool failover, bool two_phase);
 static pid_t libpqrcv_get_backend_pid(WalReceiverConn *conn);
 static WalRcvExecResult *libpqrcv_exec(WalReceiverConn *conn,
 									   const char *query,
@@ -1121,15 +1121,16 @@ libpqrcv_create_slot(WalReceiverConn *conn, const char *slotname,
  */
 static void
 libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-					bool failover)
+					bool failover, bool two_phase)
 {
 	StringInfoData cmd;
 	PGresult   *res;
 
 	initStringInfo(&cmd);
-	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( FAILOVER %s )",
+	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( FAILOVER %s, TWO_PHASE %s )",
 					 quote_identifier(slotname),
-					 failover ? "true" : "false");
+					 failover ? "true" : "false",
+					 two_phase ? "true" : "false");
 
 	res = libpqrcv_PQexec(conn->streamConn, cmd.data);
 	pfree(cmd.data);
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 66070e9131..548f6e0edb 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -623,6 +623,28 @@ logicalrep_worker_stop(Oid subid, Oid relid)
 	LWLockRelease(LogicalRepWorkerLock);
 }
 
+/*
+ * Stop all the subscription workers.
+ */
+void
+logicalrep_workers_stop(Oid subid)
+{
+	List	   *subworkers;
+	ListCell   *lc;
+
+	LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
+	/* XXX clarify the reason why not only running workers are listed. */
+	subworkers = logicalrep_workers_find(subid, false);
+	LWLockRelease(LogicalRepWorkerLock);
+	foreach(lc, subworkers)
+	{
+		LogicalRepWorker *w = (LogicalRepWorker *) lfirst(lc);
+
+		logicalrep_worker_stop(w->subid, w->relid);
+	}
+	list_free(subworkers);
+}
+
 /*
  * Stop the given logical replication parallel apply worker.
  *
diff --git a/src/backend/replication/logical/worker.c b/src/backend/replication/logical/worker.c
index b5a80fe3e8..dcf656fd45 100644
--- a/src/backend/replication/logical/worker.c
+++ b/src/backend/replication/logical/worker.c
@@ -402,7 +402,6 @@ static void apply_handle_tuple_routing(ApplyExecutionData *edata,
 									   CmdType operation);
 
 /* Compute GID for two_phase transactions */
-static void TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid, int szgid);
 
 /* Functions for skipping changes */
 static void maybe_start_skipping_changes(XLogRecPtr finish_lsn);
@@ -3911,7 +3910,7 @@ maybe_reread_subscription(void)
 	/* !slotname should never happen when enabled is true. */
 	Assert(newsub->slotname);
 
-	/* two-phase should not be altered */
+	/* two-phase cannot be altered while the worker exists */
 	Assert(newsub->twophasestate == MySubscription->twophasestate);
 
 	/*
@@ -4396,24 +4395,6 @@ cleanup_subxact_info()
 	subxact_data.nsubxacts_max = 0;
 }
 
-/*
- * Form the prepared transaction GID for two_phase transactions.
- *
- * Return the GID in the supplied buffer.
- */
-static void
-TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid, int szgid)
-{
-	Assert(subid != InvalidRepOriginId);
-
-	if (!TransactionIdIsValid(xid))
-		ereport(ERROR,
-				(errcode(ERRCODE_PROTOCOL_VIOLATION),
-				 errmsg_internal("invalid two-phase transaction ID")));
-
-	snprintf(gid, szgid, "pg_gid_%u_%u", subid, xid);
-}
-
 /*
  * Common function to run the apply loop with error handling. Disable the
  * subscription, if necessary.
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index aa4ea387da..d0c8d5a4df 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -804,8 +804,10 @@ ReplicationSlotDrop(const char *name, bool nowait)
  * Change the definition of the slot identified by the specified name.
  */
 void
-ReplicationSlotAlter(const char *name, bool failover)
+ReplicationSlotAlter(const char *name, bool failover, bool two_phase)
 {
+	bool		update_slot = false;
+
 	Assert(MyReplicationSlot == NULL);
 
 	ReplicationSlotAcquire(name, false);
@@ -854,6 +856,20 @@ ReplicationSlotAlter(const char *name, bool failover)
 		MyReplicationSlot->data.failover = failover;
 		SpinLockRelease(&MyReplicationSlot->mutex);
 
+		update_slot = true;
+	}
+
+	if (MyReplicationSlot->data.two_phase != two_phase)
+	{
+		SpinLockAcquire(&MyReplicationSlot->mutex);
+		MyReplicationSlot->data.two_phase = two_phase;
+		SpinLockRelease(&MyReplicationSlot->mutex);
+
+		update_slot = true;
+	}
+
+	if (update_slot)
+	{
 		ReplicationSlotMarkDirty();
 		ReplicationSlotSave();
 	}
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index c623b07cf0..2e6ca35049 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1411,9 +1411,11 @@ DropReplicationSlot(DropReplicationSlotCmd *cmd)
  * Process extra options given to ALTER_REPLICATION_SLOT.
  */
 static void
-ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd, bool *failover)
+ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd,
+						  bool *failover, bool *two_phase)
 {
 	bool		failover_given = false;
+	bool		two_phase_given = false;
 
 	/* Parse options */
 	foreach_ptr(DefElem, defel, cmd->options)
@@ -1427,6 +1429,15 @@ ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd, bool *failover)
 			failover_given = true;
 			*failover = defGetBoolean(defel);
 		}
+		else if (strcmp(defel->defname, "two_phase") == 0)
+		{
+			if (two_phase_given)
+				ereport(ERROR,
+						(errcode(ERRCODE_SYNTAX_ERROR),
+						 errmsg("conflicting or redundant options")));
+			two_phase_given = true;
+			*two_phase = defGetBoolean(defel);
+		}
 		else
 			elog(ERROR, "unrecognized option: %s", defel->defname);
 	}
@@ -1439,9 +1450,10 @@ static void
 AlterReplicationSlot(AlterReplicationSlotCmd *cmd)
 {
 	bool		failover = false;
+	bool		two_phase = false;
 
-	ParseAlterReplSlotOptions(cmd, &failover);
-	ReplicationSlotAlter(cmd->slotname, failover);
+	ParseAlterReplSlotOptions(cmd, &failover, &two_phase);
+	ReplicationSlotAlter(cmd->slotname, failover, two_phase);
 }
 
 /*
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
index d453e224d9..891face1b6 100644
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -1948,7 +1948,7 @@ psql_completion(const char *text, int start, int end)
 	else if (HeadMatches("ALTER", "SUBSCRIPTION", MatchAny) && TailMatches("SET", "("))
 		COMPLETE_WITH("binary", "disable_on_error", "failover", "origin",
 					  "password_required", "run_as_owner", "slot_name",
-					  "streaming", "synchronous_commit");
+					  "streaming", "synchronous_commit", "two_phase");
 	/* ALTER SUBSCRIPTION <name> SKIP ( */
 	else if (HeadMatches("ALTER", "SUBSCRIPTION", MatchAny) && TailMatches("SKIP", "("))
 		COMPLETE_WITH("lsn");
diff --git a/src/include/access/twophase.h b/src/include/access/twophase.h
index 56248c0006..d37e06fdee 100644
--- a/src/include/access/twophase.h
+++ b/src/include/access/twophase.h
@@ -62,4 +62,9 @@ extern void PrepareRedoRemove(TransactionId xid, bool giveWarning);
 extern void restoreTwoPhaseData(void);
 extern bool LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 						TimestampTz origin_prepare_timestamp);
+
+extern void TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid,
+								   int szgid);
+extern bool LookupGXactBySubid(Oid subid);
+
 #endif							/* TWOPHASE_H */
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 1bc80960ef..014e216cf5 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -243,7 +243,8 @@ extern void ReplicationSlotCreate(const char *name, bool db_specific,
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
 extern void ReplicationSlotDropAcquired(void);
-extern void ReplicationSlotAlter(const char *name, bool failover);
+extern void ReplicationSlotAlter(const char *name, bool failover,
+								 bool two_phase);
 
 extern void ReplicationSlotAcquire(const char *name, bool nowait);
 extern void ReplicationSlotRelease(void);
diff --git a/src/include/replication/walreceiver.h b/src/include/replication/walreceiver.h
index 12f71fa99b..31fa1257ec 100644
--- a/src/include/replication/walreceiver.h
+++ b/src/include/replication/walreceiver.h
@@ -372,12 +372,13 @@ typedef char *(*walrcv_create_slot_fn) (WalReceiverConn *conn,
 /*
  * walrcv_alter_slot_fn
  *
- * Change the definition of a replication slot. Currently, it only supports
- * changing the failover property of the slot.
+ * Change the definition of a replication slot. Currently, it supports
+ * changing the failover and the two_phase property of the slot.
  */
 typedef void (*walrcv_alter_slot_fn) (WalReceiverConn *conn,
 									  const char *slotname,
-									  bool failover);
+									  bool failover,
+									  bool two_phase);
 
 /*
  * walrcv_get_backend_pid_fn
@@ -455,8 +456,8 @@ extern PGDLLIMPORT WalReceiverFunctionsType *WalReceiverFunctions;
 	WalReceiverFunctions->walrcv_send(conn, buffer, nbytes)
 #define walrcv_create_slot(conn, slotname, temporary, two_phase, failover, snapshot_action, lsn) \
 	WalReceiverFunctions->walrcv_create_slot(conn, slotname, temporary, two_phase, failover, snapshot_action, lsn)
-#define walrcv_alter_slot(conn, slotname, failover) \
-	WalReceiverFunctions->walrcv_alter_slot(conn, slotname, failover)
+#define walrcv_alter_slot(conn, slotname, failover, two_phase) \
+	WalReceiverFunctions->walrcv_alter_slot(conn, slotname, failover, two_phase)
 #define walrcv_get_backend_pid(conn) \
 	WalReceiverFunctions->walrcv_get_backend_pid(conn)
 #define walrcv_exec(conn, exec, nRetTypes, retTypes) \
diff --git a/src/include/replication/worker_internal.h b/src/include/replication/worker_internal.h
index 515aefd519..d5428263c1 100644
--- a/src/include/replication/worker_internal.h
+++ b/src/include/replication/worker_internal.h
@@ -246,6 +246,7 @@ extern bool logicalrep_worker_launch(LogicalRepWorkerType wtype,
 									 Oid userid, Oid relid,
 									 dsm_handle subworker_dsm);
 extern void logicalrep_worker_stop(Oid subid, Oid relid);
+extern void logicalrep_workers_stop(Oid subid);
 extern void logicalrep_pa_worker_stop(ParallelApplyWorkerInfo *winfo);
 extern void logicalrep_worker_wakeup(Oid subid, Oid relid);
 extern void logicalrep_worker_wakeup_ptr(LogicalRepWorker *worker);
diff --git a/src/test/regress/expected/subscription.out b/src/test/regress/expected/subscription.out
index 0f2a25cdc1..51fa4b9690 100644
--- a/src/test/regress/expected/subscription.out
+++ b/src/test/regress/expected/subscription.out
@@ -377,10 +377,7 @@ HINT:  To initiate replication, you must manually create the replication slot, e
  regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | p                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
---fail - alter of two_phase option not supported.
-ALTER SUBSCRIPTION regress_testsub SET (two_phase = false);
-ERROR:  unrecognized subscription parameter: "two_phase"
--- but can alter streaming when two_phase enabled
+-- We can alter streaming when two_phase enabled
 ALTER SUBSCRIPTION regress_testsub SET (streaming = true);
 \dRs+
                                                                                                                 List of subscriptions
diff --git a/src/test/regress/sql/subscription.sql b/src/test/regress/sql/subscription.sql
index 3e5ba4cb8c..a3886d79ca 100644
--- a/src/test/regress/sql/subscription.sql
+++ b/src/test/regress/sql/subscription.sql
@@ -256,10 +256,7 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUBLICATION testpub WITH (connect = false, two_phase = true);
 
 \dRs+
---fail - alter of two_phase option not supported.
-ALTER SUBSCRIPTION regress_testsub SET (two_phase = false);
-
--- but can alter streaming when two_phase enabled
+-- We can alter streaming when two_phase enabled
 ALTER SUBSCRIPTION regress_testsub SET (streaming = true);
 
 \dRs+
diff --git a/src/test/subscription/t/021_twophase.pl b/src/test/subscription/t/021_twophase.pl
index 9437cd4c3b..72df258000 100644
--- a/src/test/subscription/t/021_twophase.pl
+++ b/src/test/subscription/t/021_twophase.pl
@@ -367,6 +367,75 @@ $result =
   $node_subscriber->safe_psql('postgres', "SELECT count(*) FROM tab_copy;");
 is($result, qq(2), 'replicated data in subscriber table');
 
+# Clean up
+$node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub");
+
+###############################
+# Disable the subscription and alter it to two_phase = false,
+# then verify that the altered subscription reflects the two_phase option.
+###############################
+
+# Alter subscription two_phase to false
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy DISABLE");
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = false)");
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy ENABLE");
+
+# Wait for subscription startup
+$node_subscriber->wait_for_subscription_sync($node_publisher, $appname_copy);
+
+# Make sure that the two-phase is disabled on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+       "SELECT subtwophasestate FROM pg_subscription WHERE subname = 'tap_sub_copy';"
+);
+is($result, qq(d), 'two-phase should be disabled');
+
+# Now do a prepare on the publisher and make sure that it is not replicated.
+$node_publisher->safe_psql(
+       'postgres', qq{
+    BEGIN;
+    INSERT INTO tab_copy VALUES (100);
+    PREPARE TRANSACTION 'newgid';
+	});
+
+# Wait for the subscriber to catchup
+$node_publisher->wait_for_catchup($appname_copy);
+
+# Make sure there are no prepared transactions on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT count(*) FROM pg_prepared_xacts;");
+is($result, qq(0), 'should be no prepared transactions on subscriber');
+
+# Now commit the insert and verify that it IS replicated
+$node_publisher->safe_psql('postgres', "COMMIT PREPARED 'newgid';");
+
+# Wait for the subscriber to catchup
+$node_publisher->wait_for_catchup($appname_copy);
+
+# Make sure that the committed transaction is replicated.
+$result =
+	$node_subscriber->safe_psql('postgres', "SELECT count(*) FROM tab_copy;");
+is($result, qq(3), 'replicated data in subscriber table');
+
+# Alter subscription two_phase to true
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy DISABLE");
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = true)");
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy ENABLE");
+
+# Wait for subscription startup
+$node_subscriber->wait_for_subscription_sync($node_publisher, $appname_copy);
+
+# Make sure that the two-phase is enabled on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT subtwophasestate FROM pg_subscription WHERE subname = 'tap_sub_copy';"
+);
+is($result, qq(e), 'two-phase should be enabled');
+
 $node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub_copy;");
 $node_publisher->safe_psql('postgres', "DROP PUBLICATION tap_pub_copy;");
 
@@ -374,8 +443,6 @@ $node_publisher->safe_psql('postgres', "DROP PUBLICATION tap_pub_copy;");
 # check all the cleanup
 ###############################
 
-$node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub");
-
 $result = $node_subscriber->safe_psql('postgres',
 	"SELECT count(*) FROM pg_subscription");
 is($result, qq(0), 'check subscription was dropped on subscriber');
-- 
2.43.0

From c2e94d34ae70a07030bb549e6f29530ccee443ad Mon Sep 17 00:00:00 2001
From: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Date: Wed, 17 Apr 2024 06:18:23 +0000
Subject: [PATCH v11 2/4] Alter slot option two_phase only when altering "true"
 to "false"
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Since the two_phase option is controlled by both the publisher (as a slot option)
and the subscriber (as a subscription option), the slot option must also be
modified.

Regarding the false->true case, the backend process alters the subtwophase to
LOGICALREP_TWOPHASE_STATE_PENDING once. After the subscription is enabled, a new
logical replication worker requests to change the two_phase option of its slot
from pending to true after the initial data synchronization is done. The code
path is the same as the case in which two_phase is initially set to true, so
there is no need to do something remarkable. However, for the true->false case,
the backend must connect to the publisher and expressly change the parameter
because the apply worker does not alter the option to false. Because this
operation cannot be rolled back, altering the two_phase parameter from "true"
to "false" within a transaction is prohibited.
---
 doc/src/sgml/ref/alter_subscription.sgml      |  2 +-
 src/backend/commands/subscriptioncmds.c       | 42 ++++++--
 .../libpqwalreceiver/libpqwalreceiver.c       | 23 +++--
 src/include/replication/walreceiver.h         |  5 +-
 src/test/subscription/meson.build             |  1 +
 src/test/subscription/t/099_twophase_added.pl | 96 +++++++++++++++++++
 6 files changed, 153 insertions(+), 16 deletions(-)
 create mode 100644 src/test/subscription/t/099_twophase_added.pl

diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index 88e9a72147..0c2894a94e 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -70,7 +70,7 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
    <command>ALTER SUBSCRIPTION ... {SET|ADD|DROP} PUBLICATION ...</command>
    with <literal>refresh</literal> option as <literal>true</literal>,
    <command>ALTER SUBSCRIPTION ... SET (failover = on|off)</command> and
-   <command>ALTER SUBSCRIPTION ... SET (two_phase = on|off)</command>
+   <command>ALTER SUBSCRIPTION ... SET (two_phase = off)</command>
    cannot be executed inside a transaction block.
 
    These commands also cannot be executed when the subscription has
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index 90d967eb7c..ff733e3810 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -1097,6 +1097,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 	Form_pg_subscription form;
 	bits32		supported_opts;
 	SubOpts		opts = {0};
+	bool		update_failover;
+	bool		update_two_phase;
 
 	rel = table_open(SubscriptionRelationId, RowExclusiveLock);
 
@@ -1186,10 +1188,24 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 								 errhint("Resolve these transactions and try again")));
 
 					/*
-					 * The changed two_phase option of the slot can't be rolled
-					 * back.
+					 * Altering the parameter from "true" to "false" within a
+					 * transaction is prohibited. Since the apply worker does
+					 * not alter the slot option to false, the backend must
+					 * connect to the publisher and expressly change the
+					 * parameter.
+					 *
+					 * There is no need to do something remarkable regarding
+					 * the "false" to "true" case; the backend process alters
+					 * subtwophase to LOGICALREP_TWOPHASE_STATE_PENDING once.
+					 * After the subscription is enabled, a new logical
+					 * replication worker requests to change the two_phase
+					 * option of its slot from pending to true when the initial
+					 * data synchronization is done. The code path is the same
+					 * as the case in which two_phase is initially set to true.
 					 */
-					PreventInTransactionBlock(isTopLevel, "ALTER SUBSCRIPTION ... SET (two_phase)");
+					if (!opts.twophase)
+						PreventInTransactionBlock(isTopLevel,
+												  "ALTER SUBSCRIPTION ... SET (two_phase = false)");
 
 					/* Change system catalog acoordingly */
 					values[Anum_pg_subscription_subtwophasestate - 1] =
@@ -1547,14 +1563,24 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 	}
 
 	/*
-	 * Try to acquire the connection necessary for altering slot.
+	 * Check the need to alter the replication slot. Failover and two_phase
+	 * options are controlled by both the publisher (as a slot option) and the
+	 * subscriber (as a subscription option). The slot option must be altered
+	 * only when changing "true" to "false". The reason has already been
+	 * described in the ALTER_SUBSCRIPTION_OPTIONS section of this function.
+	 */
+	update_failover = replaces[Anum_pg_subscription_subfailover - 1];
+	update_two_phase = (replaces[Anum_pg_subscription_subtwophasestate - 1] &&
+						!opts.twophase);
+
+	/*
+	 * Try to acquire the connection necessary for altering slot, if needed.
 	 *
 	 * This has to be at the end because otherwise if there is an error while
 	 * doing the database operations we won't be able to rollback altered
 	 * slot.
 	 */
-	if (replaces[Anum_pg_subscription_subfailover - 1] ||
-		replaces[Anum_pg_subscription_subtwophasestate - 1])
+	if (update_failover || update_two_phase)
 	{
 		bool		must_use_password;
 		char	   *err;
@@ -1574,7 +1600,9 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 
 		PG_TRY();
 		{
-			walrcv_alter_slot(wrconn, sub->slotname, opts.failover, opts.twophase);
+			walrcv_alter_slot(wrconn, sub->slotname,
+							  update_failover ? &opts.failover : NULL,
+							  update_two_phase ? &opts.twophase : NULL);
 		}
 		PG_FINALLY();
 		{
diff --git a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
index 998bbd517a..ff013aa987 100644
--- a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
+++ b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
@@ -80,7 +80,7 @@ static char *libpqrcv_create_slot(WalReceiverConn *conn,
 								  CRSSnapshotAction snapshot_action,
 								  XLogRecPtr *lsn);
 static void libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-								bool failover, bool two_phase);
+								const bool *failover, const bool *two_phase);
 static pid_t libpqrcv_get_backend_pid(WalReceiverConn *conn);
 static WalRcvExecResult *libpqrcv_exec(WalReceiverConn *conn,
 									   const char *query,
@@ -1121,16 +1121,27 @@ libpqrcv_create_slot(WalReceiverConn *conn, const char *slotname,
  */
 static void
 libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-					bool failover, bool two_phase)
+					const bool *failover, const bool *two_phase)
 {
 	StringInfoData cmd;
 	PGresult   *res;
 
 	initStringInfo(&cmd);
-	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( FAILOVER %s, TWO_PHASE %s )",
-					 quote_identifier(slotname),
-					 failover ? "true" : "false",
-					 two_phase ? "true" : "false");
+	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( ",
+					 quote_identifier(slotname));
+
+	if (failover)
+		appendStringInfo(&cmd, "FAILOVER %s",
+						 *failover ? "true" : "false");
+
+	if (failover && two_phase)
+		appendStringInfo(&cmd, ", ");
+
+	if (two_phase)
+		appendStringInfo(&cmd, "TWO_PHASE %s",
+						 *two_phase ? "true" : "false");
+
+	appendStringInfoString(&cmd, " );");
 
 	res = libpqrcv_PQexec(conn->streamConn, cmd.data);
 	pfree(cmd.data);
diff --git a/src/include/replication/walreceiver.h b/src/include/replication/walreceiver.h
index 31fa1257ec..7ffa5a58b3 100644
--- a/src/include/replication/walreceiver.h
+++ b/src/include/replication/walreceiver.h
@@ -377,8 +377,9 @@ typedef char *(*walrcv_create_slot_fn) (WalReceiverConn *conn,
  */
 typedef void (*walrcv_alter_slot_fn) (WalReceiverConn *conn,
 									  const char *slotname,
-									  bool failover,
-									  bool two_phase);
+									  const bool *failover,
+									  const bool *two_phase);
+
 
 /*
  * walrcv_get_backend_pid_fn
diff --git a/src/test/subscription/meson.build b/src/test/subscription/meson.build
index c591cd7d61..b4bd522c3d 100644
--- a/src/test/subscription/meson.build
+++ b/src/test/subscription/meson.build
@@ -40,6 +40,7 @@ tests += {
       't/031_column_list.pl',
       't/032_subscribe_use_index.pl',
       't/033_run_as_table_owner.pl',
+      't/099_twophase_added.pl',
       't/100_bugs.pl',
     ],
   },
diff --git a/src/test/subscription/t/099_twophase_added.pl b/src/test/subscription/t/099_twophase_added.pl
new file mode 100644
index 0000000000..ac08969b32
--- /dev/null
+++ b/src/test/subscription/t/099_twophase_added.pl
@@ -0,0 +1,96 @@
+# Copyright (c) 2024, PostgreSQL Global Development Group
+
+# Additional tests for altering two_phase option
+use strict;
+use warnings FATAL => 'all';
+use PostgreSQL::Test::Cluster;
+use PostgreSQL::Test::Utils;
+use Test::More;
+
+# Initialize publisher node
+my $node_publisher = PostgreSQL::Test::Cluster->new('publisher');
+$node_publisher->init(allows_streaming => 'logical');
+$node_publisher->append_conf('postgresql.conf',
+	qq(max_prepared_transactions = 10));
+$node_publisher->start;
+
+# Create subscriber node
+my $node_subscriber = PostgreSQL::Test::Cluster->new('subscriber');
+$node_subscriber->init;
+$node_subscriber->append_conf('postgresql.conf',
+	qq(max_prepared_transactions = 10
+	log_min_messages = debug1));
+$node_subscriber->start;
+
+# Define tables on both nodes
+$node_publisher->safe_psql('postgres',
+    "CREATE TABLE tab_full (a int PRIMARY KEY);");
+$node_subscriber->safe_psql('postgres',
+	"CREATE TABLE tab_full (a int PRIMARY KEY)");
+
+# Setup logical replication, with two_phase = "false"
+my $publisher_connstr = $node_publisher->connstr . ' dbname=postgres';
+$node_publisher->safe_psql('postgres',
+	"CREATE PUBLICATION pub FOR ALL TABLES");
+
+my $log_offset = -s $node_subscriber->logfile;
+
+$node_subscriber->safe_psql(
+	'postgres', "
+	CREATE SUBSCRIPTION regress_sub
+	CONNECTION '$publisher_connstr' PUBLICATION pub
+	WITH (two_phase = false, copy_data = false, failover = false)");
+
+# Verify the started worker recognized two_phase was disabled
+$node_subscriber->wait_for_log(
+	'logical replication apply worker for subscription "regress_sub" two_phase is DISABLED', $log_offset);
+
+#####################
+# Check the case that prepared transactions exist on the publisher node.
+#
+# Since the two_phase is "false", then normally, this PREPARE will do nothing
+# until the COMMIT PREPARED, but in this test, we toggle the two_phase to
+# "true" again before the COMMIT PREPARED happens.
+
+# Prepare a transaction to insert some tuples into the table
+$node_publisher->safe_psql(
+	'postgres', "
+	BEGIN;
+	INSERT INTO tab_full VALUES (generate_series(1, 5));
+	PREPARE TRANSACTION 'test_prepared_tab_full';");
+
+$node_publisher->wait_for_catchup('regress_sub');
+
+# Verify the prepared transaction is not yet replicated to the subscriber
+# because two_phase is set to "false".
+my $result = $node_subscriber->safe_psql('postgres',
+    "SELECT count(*) FROM pg_prepared_xacts;");
+is($result, q(0), "transaction is not prepared on subscriber");
+
+$log_offset = -s $node_subscriber->logfile;
+
+# Toggle the two_phase to "true" *before* the COMMIT PREPARED. Since we are the
+# special path for the case where both two_phase and failover are altered, it
+# is also set to "true".
+$node_subscriber->safe_psql(
+    'postgres', "
+    ALTER SUBSCRIPTION regress_sub DISABLE;
+    ALTER SUBSCRIPTION regress_sub SET (two_phase = true, failover = true);
+    ALTER SUBSCRIPTION regress_sub ENABLE;");
+
+# Verify the started worker recognized two_phase was enabled
+$node_subscriber->wait_for_log(
+	'logical replication apply worker for subscription "regress_sub" two_phase is ENABLED', $log_offset);
+
+# And do COMMIT PREPARED the prepared transaction
+$node_publisher->safe_psql('postgres',
+    "COMMIT PREPARED 'test_prepared_tab_full';");
+$node_publisher->wait_for_catchup('regress_sub');
+
+# Verify inserted tuples are replicated
+$result = $node_subscriber->safe_psql('postgres',
+    "SELECT count(*) FROM tab_full;");
+is($result, q(5),
+   "prepared transactions done before altering can be replicated");
+
+done_testing();
-- 
2.43.0

From 25e0c246fe8d1f770b2b3255e6275cfc5600b98b Mon Sep 17 00:00:00 2001
From: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Date: Mon, 8 Apr 2024 12:39:12 +0000
Subject: [PATCH v11 3/4] Abort prepared transactions while altering two_phase
 to off

If we alter the two_phase parameter from "on" to "off" and there are prepared
transactions on the subscriber, they won't be resolved. To avoid this issue, we
allow the backend to abort all prepared transactions while altering the
subscription.
---
 doc/src/sgml/ref/alter_subscription.sgml      | 11 ++-
 src/backend/access/transam/twophase.c         | 17 ++---
 src/backend/commands/subscriptioncmds.c       | 76 ++++++++++++-------
 src/include/access/twophase.h                 |  3 +-
 src/test/subscription/t/099_twophase_added.pl | 45 +++++++++++
 5 files changed, 110 insertions(+), 42 deletions(-)

diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index 0c2894a94e..2c6502275a 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -233,8 +233,6 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>, and
       <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>.
       Only a superuser can set <literal>password_required = false</literal>.
-      The <literal>two_phase</literal> parameter can only be altered when the
-      subscription is disabled.
      </para>
 
      <para>
@@ -256,6 +254,15 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>
       option is enabled.
      </para>
+
+     <para>
+      The <literal>two_phase</literal> parameter can only be altered when the
+      subscription is disabled. When altering the parameter from <literal>true</literal>
+      to <literal>false</literal>, the backend process checks for any incomplete
+      prepared transactions done by the logical replication worker (from when
+      <literal>two_phase</literal> parameter was still <literal>true</literal>)
+      and, if any are found, those are aborted.
+     </para>
     </listitem>
    </varlistentry>
 
diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index 66fa591eb5..f384bd8c0a 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -2720,13 +2720,13 @@ IsTwoPhaseTransactionGidForSubid(Oid subid, char *gid)
 }
 
 /*
- * LookupGXactBySubid
- *		Check if the prepared transaction done by apply worker exists.
+ * GetGidListBySubid
+ *      Get a list of GIDs which is PREPARE'd by the given subscription.
  */
-bool
-LookupGXactBySubid(Oid subid)
+List *
+GetGidListBySubid(Oid subid)
 {
-	bool		found = false;
+	List *list = NIL;
 
 	LWLockAcquire(TwoPhaseStateLock, LW_SHARED);
 	for (int i = 0; i < TwoPhaseState->numPrepXacts; i++)
@@ -2736,11 +2736,8 @@ LookupGXactBySubid(Oid subid)
 		/* Ignore not-yet-valid GIDs. */
 		if (gxact->valid &&
 			IsTwoPhaseTransactionGidForSubid(subid, gxact->gid))
-		{
-			found = true;
-			break;
-		}
+			list = lappend(list, pstrdup(gxact->gid));
 	}
 	LWLockRelease(TwoPhaseStateLock);
-	return found;
+	return list;
 }
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index ff733e3810..82cad60547 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -1157,6 +1157,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 
 				if (IsSet(opts.specified_opts, SUBOPT_TWOPHASE_COMMIT))
 				{
+					char subtwophase;
+
 					/*
 					 * Do not allow changing the two_phase option if the
 					 * subscription is enabled. This is because the two_phase
@@ -1176,42 +1178,58 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 					logicalrep_workers_stop(subid);
 
 					/*
-					 * two_phase cannot be disabled if there are any
-					 * uncommitted prepared transactions present.
-					 */
-					if (!opts.twophase &&
-						form->subtwophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
-						LookupGXactBySubid(subid))
-						ereport(ERROR,
-								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-								 errmsg("cannot disable two_phase when uncommitted prepared transactions present"),
-								 errhint("Resolve these transactions and try again")));
-
-					/*
-					 * Altering the parameter from "true" to "false" within a
-					 * transaction is prohibited. Since the apply worker does
-					 * not alter the slot option to false, the backend must
-					 * connect to the publisher and expressly change the
-					 * parameter.
-					 *
-					 * There is no need to do something remarkable regarding
-					 * the "false" to "true" case; the backend process alters
-					 * subtwophase to LOGICALREP_TWOPHASE_STATE_PENDING once.
-					 * After the subscription is enabled, a new logical
-					 * replication worker requests to change the two_phase
-					 * option of its slot from pending to true when the initial
-					 * data synchronization is done. The code path is the same
-					 * as the case in which two_phase is initially set to true.
+					 * If two_phase was previously enabled, there is a
+					 * possibility that transactions have already been
+					 * PREPARE'd. They must be checked and rolled back.
 					 */
 					if (!opts.twophase)
+					{
+						List *prepared_xacts;
+
+						/*
+						 * Altering the parameter from "true" to "false" within
+						 * a transaction is prohibited. Since the apply worker
+						 * does not alter the slot option to false, the backend
+						 * must connect to the publisher and expressly change
+						 * the parameter.
+						 *
+						 * There is no need to do something remarkable
+						 * regarding the "false" to "true" case; the backend
+						 * process alters subtwophase to
+						 * LOGICALREP_TWOPHASE_STATE_PENDING once. After the
+						 * subscription is enabled, a new logical replication
+						 * worker requests to change the two_phase option of
+						 * its slot from pending to true when the initial data
+						 * synchronization is done. The code path is the same
+						 * as the case in which two_phase is initially set to
+						 * true.
+						 */
 						PreventInTransactionBlock(isTopLevel,
 												  "ALTER SUBSCRIPTION ... SET (two_phase = false)");
 
+						/*
+						 * To prevent prepared transactions from being
+						 * isolated, they must manually be aborted.
+						 */
+						if (sub->twophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
+							(prepared_xacts = GetGidListBySubid(subid)) != NIL)
+						{
+							/* Abort all listed transactions */
+							foreach_ptr(char, gid, prepared_xacts)
+								FinishPreparedTransaction(gid, false);
+
+							list_free_deep(prepared_xacts);
+						}
+
+						subtwophase = LOGICALREP_TWOPHASE_STATE_DISABLED;
+					}
+					else
+						subtwophase = LOGICALREP_TWOPHASE_STATE_PENDING;
+
+
 					/* Change system catalog acoordingly */
 					values[Anum_pg_subscription_subtwophasestate - 1] =
-						CharGetDatum(opts.twophase ?
-									 LOGICALREP_TWOPHASE_STATE_PENDING :
-									 LOGICALREP_TWOPHASE_STATE_DISABLED);
+						CharGetDatum(subtwophase);
 					replaces[Anum_pg_subscription_subtwophasestate - 1] = true;
 				}
 
diff --git a/src/include/access/twophase.h b/src/include/access/twophase.h
index d37e06fdee..f7a5cf0c12 100644
--- a/src/include/access/twophase.h
+++ b/src/include/access/twophase.h
@@ -18,6 +18,7 @@
 #include "access/xlogdefs.h"
 #include "datatype/timestamp.h"
 #include "storage/lock.h"
+#include "nodes/pg_list.h"
 
 /*
  * GlobalTransactionData is defined in twophase.c; other places have no
@@ -65,6 +66,6 @@ extern bool LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 
 extern void TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid,
 								   int szgid);
-extern bool LookupGXactBySubid(Oid subid);
+extern List *GetGidListBySubid(Oid subid);
 
 #endif							/* TWOPHASE_H */
diff --git a/src/test/subscription/t/099_twophase_added.pl b/src/test/subscription/t/099_twophase_added.pl
index ac08969b32..5a9a6c6476 100644
--- a/src/test/subscription/t/099_twophase_added.pl
+++ b/src/test/subscription/t/099_twophase_added.pl
@@ -93,4 +93,49 @@ $result = $node_subscriber->safe_psql('postgres',
 is($result, q(5),
    "prepared transactions done before altering can be replicated");
 
+#####################
+# Check the case that prepared transactions exist on the subscriber node
+#
+# If the two_phase is altering from "true" to "false" and there are prepared
+# transactions on the subscriber, they must be aborted. This test checks it.
+
+# Prepare a transaction to insert some tuples into the table
+$node_publisher->safe_psql(
+	'postgres', "
+	BEGIN;
+	INSERT INTO tab_full VALUES (generate_series(6, 10));
+	PREPARE TRANSACTION 'test_prepared_tab_full';");
+
+$node_publisher->wait_for_catchup('regress_sub');
+
+# Verify the prepared transaction has been replicated to the subscriber because
+# two_phase is set to "true".
+$result = $node_subscriber->safe_psql('postgres',
+    "SELECT count(*) FROM pg_prepared_xacts;");
+is($result, q(1), "transaction has been prepared on subscriber");
+
+# Toggle the two_phase to "false" before the COMMIT PREPARED
+$node_subscriber->safe_psql(
+    'postgres', "
+    ALTER SUBSCRIPTION regress_sub DISABLE;
+    ALTER SUBSCRIPTION regress_sub SET (two_phase = false);
+    ALTER SUBSCRIPTION regress_sub ENABLE;");
+
+# Verify any prepared transactions are aborted because two_phase is changed to
+# "false".
+$result = $node_subscriber->safe_psql('postgres',
+    "SELECT count(*) FROM pg_prepared_xacts;");
+is($result, q(0), "prepared transaction done by worker is aborted");
+
+# Do COMMIT PREPARED the prepared transaction
+$node_publisher->safe_psql( 'postgres',
+    "COMMIT PREPARED 'test_prepared_tab_full';");
+$node_publisher->wait_for_catchup('regress_sub');
+
+# Verify inserted tuples are replicated
+$result = $node_subscriber->safe_psql('postgres',
+    "SELECT count(10) FROM tab_full;");
+is($result, q(10),
+   "prepared transactions on publisher can be replicated");
+
 done_testing();
-- 
2.43.0

From e872bcaeedf4c203b5331ad9efb39945d89baa0d Mon Sep 17 00:00:00 2001
From: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Date: Fri, 19 Apr 2024 11:03:19 +0000
Subject: [PATCH v11 4/4] Add force_alter option for ALTER SUBSCRIPTION ... SET
 command

Previously, all prepared transactions on the standby were rolled back when
toggling two_phase from "true" to "false". However, this operation may not be
expected by users. To ensure users understand what happens, we added the
"force_alter" parameter. When two_phase is toggling to "false", and there are
prepared transactions, they will be aborted only when "force_alter" is set to
true. Otherwise, an ERROR occurs.
---
 doc/src/sgml/catalogs.sgml                    |  12 ++
 doc/src/sgml/ref/alter_subscription.sgml      |  16 +-
 doc/src/sgml/ref/create_subscription.sgml     |  24 +++
 src/backend/catalog/pg_subscription.c         |   1 +
 src/backend/catalog/system_views.sql          |   2 +-
 src/backend/commands/subscriptioncmds.c       |  36 ++++-
 src/bin/pg_dump/pg_dump.c                     |  14 ++
 src/bin/pg_dump/pg_dump.h                     |   1 +
 src/bin/psql/describe.c                       |   7 +-
 src/include/catalog/pg_subscription.h         |  13 ++
 src/test/regress/expected/subscription.out    | 152 +++++++++---------
 src/test/subscription/t/099_twophase_added.pl |  39 ++++-
 12 files changed, 222 insertions(+), 95 deletions(-)

diff --git a/doc/src/sgml/catalogs.sgml b/doc/src/sgml/catalogs.sgml
index 5a6f65025b..8277475c25 100644
--- a/doc/src/sgml/catalogs.sgml
+++ b/doc/src/sgml/catalogs.sgml
@@ -8049,6 +8049,18 @@ SCRAM-SHA-256$<replaceable>&lt;iteration count&gt;</replaceable>:<replaceable>&l
       </para></entry>
      </row>
 
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>subforcealter</structfield> <type>bool</type>
+      </para>
+      <para>
+       If true, then the <link linkend="sql-altersubscription"><command>ALTER SUBSCRIPTION</command></link>
+       can disable <literal>two_phase</literal> option, even if there are
+       uncommitted prepared transactions from when <literal>two_phase</literal>
+       was enabled
+      </para></entry>
+     </row>
+
      <row>
       <entry role="catalog_table_entry"><para role="column_definition">
        <structfield>subconninfo</structfield> <type>text</type>
diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index 2c6502275a..35513e7b33 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -230,8 +230,9 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-password-required"><literal>password_required</literal></link>,
       <link linkend="sql-createsubscription-params-with-run-as-owner"><literal>run_as_owner</literal></link>,
       <link linkend="sql-createsubscription-params-with-origin"><literal>origin</literal></link>,
-      <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>, and
-      <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>.
+      <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>,
+      <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>, and
+      <link linkend="sql-createsubscription-params-with-force-alter"><literal>force_alter</literal></link>
       Only a superuser can set <literal>password_required = false</literal>.
      </para>
 
@@ -257,11 +258,12 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
 
      <para>
       The <literal>two_phase</literal> parameter can only be altered when the
-      subscription is disabled. When altering the parameter from <literal>true</literal>
-      to <literal>false</literal>, the backend process checks for any incomplete
-      prepared transactions done by the logical replication worker (from when
-      <literal>two_phase</literal> parameter was still <literal>true</literal>)
-      and, if any are found, those are aborted.
+      subscription is disabled. Altering the parameter from <literal>true</literal>
+      to <literal>false</literal> will give an error when there are prepared
+      transactions done by the logical replication worker. If you want to alter
+      the parameter forcibly in this case,
+      <link linkend="sql-createsubscription-params-with-force-alter"><literal>force_alter</literal></link>
+      option must be set to <literal>true</literal>.
      </para>
     </listitem>
    </varlistentry>
diff --git a/doc/src/sgml/ref/create_subscription.sgml b/doc/src/sgml/ref/create_subscription.sgml
index 740b7d9421..83ac52f865 100644
--- a/doc/src/sgml/ref/create_subscription.sgml
+++ b/doc/src/sgml/ref/create_subscription.sgml
@@ -428,6 +428,30 @@ CREATE SUBSCRIPTION <replaceable class="parameter">subscription_name</replaceabl
          </para>
         </listitem>
        </varlistentry>
+
+       <varlistentry id="sql-createsubscription-params-with-force-alter">
+        <term><literal>force_alter</literal> (<type>boolean</type>)</term>
+        <listitem>
+         <para>
+          Specifies if the <link linkend="sql-altersubscription"><command>ALTER SUBSCRIPTION</command></link>
+          can be forced to proceed instead of giving an error.
+         </para>
+         <para>
+          There is currently only one scenario where this parameter has any
+          effect: When altering <literal>two_phase</literal> option from
+          <literal>true</literal> to <literal>false</literal> it is possible
+          for there to be incomplete prepared transactions done by the logical
+          replication worker (from when <literal>two_phase</literal> parameter
+          was still <literal>true</literal>). If <literal>force_alter</literal>
+          is <literal>false</literal>, then this will give an error; if
+          <literal>force_alter</literal> is <literal>true</literal>, then the
+          incomplete prepared transactions are aborted and the alter will proceed.
+         </para>
+         <para>
+          The default is <literal>false</literal>.
+         </para>
+        </listitem>
+       </varlistentry>
       </variablelist></para>
 
     </listitem>
diff --git a/src/backend/catalog/pg_subscription.c b/src/backend/catalog/pg_subscription.c
index 9efc9159f2..b568fe3470 100644
--- a/src/backend/catalog/pg_subscription.c
+++ b/src/backend/catalog/pg_subscription.c
@@ -72,6 +72,7 @@ GetSubscription(Oid subid, bool missing_ok)
 	sub->passwordrequired = subform->subpasswordrequired;
 	sub->runasowner = subform->subrunasowner;
 	sub->failover = subform->subfailover;
+	sub->forcealter = subform->subforcealter;
 
 	/* Get conninfo */
 	datum = SysCacheGetAttrNotNull(SUBSCRIPTIONOID,
diff --git a/src/backend/catalog/system_views.sql b/src/backend/catalog/system_views.sql
index 53047cab5f..de3d3d8f3e 100644
--- a/src/backend/catalog/system_views.sql
+++ b/src/backend/catalog/system_views.sql
@@ -1358,7 +1358,7 @@ REVOKE ALL ON pg_replication_origin_status FROM public;
 REVOKE ALL ON pg_subscription FROM public;
 GRANT SELECT (oid, subdbid, subskiplsn, subname, subowner, subenabled,
               subbinary, substream, subtwophasestate, subdisableonerr,
-			  subpasswordrequired, subrunasowner, subfailover,
+			  subpasswordrequired, subrunasowner, subfailover, subforcealter,
               subslotname, subsynccommit, subpublications, suborigin)
     ON pg_subscription TO public;
 
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index 82cad60547..778c59736f 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -73,6 +73,7 @@
 #define SUBOPT_FAILOVER				0x00002000
 #define SUBOPT_LSN					0x00004000
 #define SUBOPT_ORIGIN				0x00008000
+#define SUBOPT_FORCE_ALTER			0x00010000
 
 /* check if the 'val' has 'bits' set */
 #define IsSet(val, bits)  (((val) & (bits)) == (bits))
@@ -100,6 +101,7 @@ typedef struct SubOpts
 	bool		failover;
 	char	   *origin;
 	XLogRecPtr	lsn;
+	bool		force_alter;
 } SubOpts;
 
 static List *fetch_table_list(WalReceiverConn *wrconn, List *publications);
@@ -162,6 +164,8 @@ parse_subscription_options(ParseState *pstate, List *stmt_options,
 		opts->failover = false;
 	if (IsSet(supported_opts, SUBOPT_ORIGIN))
 		opts->origin = pstrdup(LOGICALREP_ORIGIN_ANY);
+	if (IsSet(supported_opts, SUBOPT_FORCE_ALTER))
+		opts->force_alter = false;
 
 	/* Parse options */
 	foreach(lc, stmt_options)
@@ -367,6 +371,15 @@ parse_subscription_options(ParseState *pstate, List *stmt_options,
 			opts->specified_opts |= SUBOPT_LSN;
 			opts->lsn = lsn;
 		}
+		else if (IsSet(supported_opts, SUBOPT_FORCE_ALTER) &&
+				 strcmp(defel->defname, "force_alter") == 0)
+		{
+			if (IsSet(opts->specified_opts, SUBOPT_FORCE_ALTER))
+				errorConflictingDefElem(defel, pstate);
+
+			opts->specified_opts |= SUBOPT_FORCE_ALTER;
+			opts->force_alter = defGetBoolean(defel);
+		}
 		else
 			ereport(ERROR,
 					(errcode(ERRCODE_SYNTAX_ERROR),
@@ -604,7 +617,8 @@ CreateSubscription(ParseState *pstate, CreateSubscriptionStmt *stmt,
 					  SUBOPT_SYNCHRONOUS_COMMIT | SUBOPT_BINARY |
 					  SUBOPT_STREAMING | SUBOPT_TWOPHASE_COMMIT |
 					  SUBOPT_DISABLE_ON_ERR | SUBOPT_PASSWORD_REQUIRED |
-					  SUBOPT_RUN_AS_OWNER | SUBOPT_FAILOVER | SUBOPT_ORIGIN);
+					  SUBOPT_RUN_AS_OWNER | SUBOPT_FAILOVER | SUBOPT_ORIGIN |
+					  SUBOPT_FORCE_ALTER);
 	parse_subscription_options(pstate, stmt->options, supported_opts, &opts);
 
 	/*
@@ -711,6 +725,7 @@ CreateSubscription(ParseState *pstate, CreateSubscriptionStmt *stmt,
 	values[Anum_pg_subscription_subpasswordrequired - 1] = BoolGetDatum(opts.passwordrequired);
 	values[Anum_pg_subscription_subrunasowner - 1] = BoolGetDatum(opts.runasowner);
 	values[Anum_pg_subscription_subfailover - 1] = BoolGetDatum(opts.failover);
+	values[Anum_pg_subscription_subforcealter - 1] = BoolGetDatum(opts.force_alter);
 	values[Anum_pg_subscription_subconninfo - 1] =
 		CStringGetTextDatum(conninfo);
 	if (opts.slot_name)
@@ -1150,7 +1165,7 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 								  SUBOPT_DISABLE_ON_ERR |
 								  SUBOPT_PASSWORD_REQUIRED |
 								  SUBOPT_RUN_AS_OWNER | SUBOPT_FAILOVER |
-								  SUBOPT_ORIGIN);
+								  SUBOPT_ORIGIN | SUBOPT_FORCE_ALTER);
 
 				parse_subscription_options(pstate, stmt->options,
 										   supported_opts, &opts);
@@ -1214,6 +1229,23 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 						if (sub->twophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
 							(prepared_xacts = GetGidListBySubid(subid)) != NIL)
 						{
+							bool raise_error =
+								IsSet(opts.specified_opts, SUBOPT_FORCE_ALTER) ?
+									!opts.force_alter : !sub->forcealter;
+
+							/*
+							 * Abort prepared transactions only if
+							 * 'force_alter' option is true. Otherwise raise
+							 * an ERROR.
+							 */
+							if (raise_error)
+								ereport(ERROR,
+										(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+										 errmsg("cannot alter %s when there are prepared transactions",
+												"two_phase = false"),
+										 errhint("Resolve these transactions or set %s, and then try again.",
+												 "force_alter = true")));
+
 							/* Abort all listed transactions */
 							foreach_ptr(char, gid, prepared_xacts)
 								FinishPreparedTransaction(gid, false);
diff --git a/src/bin/pg_dump/pg_dump.c b/src/bin/pg_dump/pg_dump.c
index 5dfa7b3bcb..da45392370 100644
--- a/src/bin/pg_dump/pg_dump.c
+++ b/src/bin/pg_dump/pg_dump.c
@@ -4739,6 +4739,7 @@ getSubscriptions(Archive *fout)
 	int			i_suboriginremotelsn;
 	int			i_subenabled;
 	int			i_subfailover;
+	int			i_subforcealter;
 	int			i,
 				ntups;
 
@@ -4816,6 +4817,13 @@ getSubscriptions(Archive *fout)
 		appendPQExpBuffer(query,
 						  " false AS subfailover\n");
 
+	if (fout->remoteVersion >= 170000)
+		appendPQExpBufferStr(query,
+							 " s.subforcealter\n");
+	else
+		appendPQExpBuffer(query,
+						  " false AS subforcealter\n");
+
 	appendPQExpBufferStr(query,
 						 "FROM pg_subscription s\n");
 
@@ -4854,6 +4862,7 @@ getSubscriptions(Archive *fout)
 	i_suboriginremotelsn = PQfnumber(res, "suboriginremotelsn");
 	i_subenabled = PQfnumber(res, "subenabled");
 	i_subfailover = PQfnumber(res, "subfailover");
+	i_subforcealter = PQfnumber(res, "subforcealter");
 
 	subinfo = pg_malloc(ntups * sizeof(SubscriptionInfo));
 
@@ -4900,6 +4909,8 @@ getSubscriptions(Archive *fout)
 			pg_strdup(PQgetvalue(res, i, i_subenabled));
 		subinfo[i].subfailover =
 			pg_strdup(PQgetvalue(res, i, i_subfailover));
+		subinfo[i].subforcealter =
+			pg_strdup(PQgetvalue(res, i, i_subforcealter));
 
 		/* Decide whether we want to dump it */
 		selectDumpableObject(&(subinfo[i].dobj), fout);
@@ -5140,6 +5151,9 @@ dumpSubscription(Archive *fout, const SubscriptionInfo *subinfo)
 	if (strcmp(subinfo->subfailover, "t") == 0)
 		appendPQExpBufferStr(query, ", failover = true");
 
+	if (strcmp(subinfo->subforcealter, "t") == 0)
+		appendPQExpBufferStr(query, ", force_alter = true");
+
 	if (strcmp(subinfo->subsynccommit, "off") != 0)
 		appendPQExpBuffer(query, ", synchronous_commit = %s", fmtId(subinfo->subsynccommit));
 
diff --git a/src/bin/pg_dump/pg_dump.h b/src/bin/pg_dump/pg_dump.h
index f518a1e6d2..c666b9c113 100644
--- a/src/bin/pg_dump/pg_dump.h
+++ b/src/bin/pg_dump/pg_dump.h
@@ -672,6 +672,7 @@ typedef struct _SubscriptionInfo
 	char	   *suborigin;
 	char	   *suboriginremotelsn;
 	char	   *subfailover;
+	char	   *subforcealter;
 } SubscriptionInfo;
 
 /*
diff --git a/src/bin/psql/describe.c b/src/bin/psql/describe.c
index 3af44acef1..8e0a0b3b36 100644
--- a/src/bin/psql/describe.c
+++ b/src/bin/psql/describe.c
@@ -6537,7 +6537,7 @@ describeSubscriptions(const char *pattern, bool verbose)
 	printQueryOpt myopt = pset.popt;
 	static const bool translate_columns[] = {false, false, false, false,
 		false, false, false, false, false, false, false, false, false, false,
-	false};
+	false, false};
 
 	if (pset.sversion < 100000)
 	{
@@ -6606,6 +6606,11 @@ describeSubscriptions(const char *pattern, bool verbose)
 							  ", subfailover AS \"%s\"\n",
 							  gettext_noop("Failover"));
 
+		if (pset.sversion >= 170000)
+			appendPQExpBuffer(&buf,
+							  ", subforcealter AS \"%s\"\n",
+							  gettext_noop("Force alter"));
+
 		appendPQExpBuffer(&buf,
 						  ",  subsynccommit AS \"%s\"\n"
 						  ",  subconninfo AS \"%s\"\n",
diff --git a/src/include/catalog/pg_subscription.h b/src/include/catalog/pg_subscription.h
index 0aa14ec4a2..c23de43d79 100644
--- a/src/include/catalog/pg_subscription.h
+++ b/src/include/catalog/pg_subscription.h
@@ -98,6 +98,13 @@ CATALOG(pg_subscription,6100,SubscriptionRelationId) BKI_SHARED_RELATION BKI_ROW
 								 * slots) in the upstream database are enabled
 								 * to be synchronized to the standbys. */
 
+	bool		subforcealter;	/* True allows the ALTER SUBSCRIPTION command
+								 * to proceed under conditions that would
+								 * otherwise result in an error. Currently,
+								 * 'force_alter' only has an effect when
+								 * altering the two_phase option from "true" to
+								 * "false". */
+
 #ifdef CATALOG_VARLEN			/* variable-length fields start here */
 	/* Connection string to the publisher */
 	text		subconninfo BKI_FORCE_NOT_NULL;
@@ -151,6 +158,12 @@ typedef struct Subscription
 								 * (i.e. the main slot and the table sync
 								 * slots) in the upstream database are enabled
 								 * to be synchronized to the standbys. */
+	bool		forcealter;		/* True allows the ALTER SUBSCRIPTION command
+								 * to proceed under conditions that would
+								 * otherwise result in an error. Currently,
+								 * 'force_alter' only has an effect when
+								 * altering the two_phase option from "true" to
+								 * "false". */
 	char	   *conninfo;		/* Connection string to the publisher */
 	char	   *slotname;		/* Name of the replication slot */
 	char	   *synccommit;		/* Synchronous commit setting for worker */
diff --git a/src/test/regress/expected/subscription.out b/src/test/regress/expected/subscription.out
index 51fa4b9690..b36fc6b8f7 100644
--- a/src/test/regress/expected/subscription.out
+++ b/src/test/regress/expected/subscription.out
@@ -116,18 +116,18 @@ CREATE SUBSCRIPTION regress_testsub4 CONNECTION 'dbname=regress_doesnotexist' PU
 WARNING:  subscription was created, but is not connected
 HINT:  To initiate replication, you must manually create the replication slot, enable the subscription, and refresh the subscription.
 \dRs+ regress_testsub4
-                                                                                                                 List of subscriptions
-       Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
-------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub4 | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | none   | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                        List of subscriptions
+       Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub4 | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | none   | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub4 SET (origin = any);
 \dRs+ regress_testsub4
-                                                                                                                 List of subscriptions
-       Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
-------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub4 | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                        List of subscriptions
+       Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub4 | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 DROP SUBSCRIPTION regress_testsub3;
@@ -145,10 +145,10 @@ ALTER SUBSCRIPTION regress_testsub CONNECTION 'foobar';
 ERROR:  invalid connection string syntax: missing "=" after "foobar" in connection info string
 
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET PUBLICATION testpub2, testpub3 WITH (refresh = false);
@@ -157,10 +157,10 @@ ALTER SUBSCRIPTION regress_testsub SET (slot_name = 'newname');
 ALTER SUBSCRIPTION regress_testsub SET (password_required = false);
 ALTER SUBSCRIPTION regress_testsub SET (run_as_owner = true);
 \dRs+
-                                                                                                                     List of subscriptions
-      Name       |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |           Conninfo           | Skip LSN 
------------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+------------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | f                 | t             | f        | off                | dbname=regress_doesnotexist2 | 0/0
+                                                                                                                            List of subscriptions
+      Name       |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |           Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+------------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | f                 | t             | f        | f           | off                | dbname=regress_doesnotexist2 | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (password_required = true);
@@ -176,10 +176,10 @@ ERROR:  unrecognized subscription parameter: "create_slot"
 -- ok
 ALTER SUBSCRIPTION regress_testsub SKIP (lsn = '0/12345');
 \dRs+
-                                                                                                                     List of subscriptions
-      Name       |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |           Conninfo           | Skip LSN 
------------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+------------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist2 | 0/12345
+                                                                                                                            List of subscriptions
+      Name       |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |           Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+------------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist2 | 0/12345
 (1 row)
 
 -- ok - with lsn = NONE
@@ -188,10 +188,10 @@ ALTER SUBSCRIPTION regress_testsub SKIP (lsn = NONE);
 ALTER SUBSCRIPTION regress_testsub SKIP (lsn = '0/0');
 ERROR:  invalid WAL location (LSN): 0/0
 \dRs+
-                                                                                                                     List of subscriptions
-      Name       |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |           Conninfo           | Skip LSN 
------------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+------------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist2 | 0/0
+                                                                                                                            List of subscriptions
+      Name       |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |           Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+------------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist2 | 0/0
 (1 row)
 
 BEGIN;
@@ -223,10 +223,10 @@ ALTER SUBSCRIPTION regress_testsub_foo SET (synchronous_commit = foobar);
 ERROR:  invalid value for parameter "synchronous_commit": "foobar"
 HINT:  Available values: local, remote_write, remote_apply, on, off.
 \dRs+
-                                                                                                                       List of subscriptions
-        Name         |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |           Conninfo           | Skip LSN 
----------------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+------------------------------+----------
- regress_testsub_foo | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | t                 | f             | f        | local              | dbname=regress_doesnotexist2 | 0/0
+                                                                                                                              List of subscriptions
+        Name         |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |           Conninfo           | Skip LSN 
+---------------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+------------------------------+----------
+ regress_testsub_foo | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | t                 | f             | f        | f           | local              | dbname=regress_doesnotexist2 | 0/0
 (1 row)
 
 -- rename back to keep the rest simple
@@ -255,19 +255,19 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 WARNING:  subscription was created, but is not connected
 HINT:  To initiate replication, you must manually create the replication slot, enable the subscription, and refresh the subscription.
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | t      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | t      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (binary = false);
 ALTER SUBSCRIPTION regress_testsub SET (slot_name = NONE);
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 DROP SUBSCRIPTION regress_testsub;
@@ -279,27 +279,27 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 WARNING:  subscription was created, but is not connected
 HINT:  To initiate replication, you must manually create the replication slot, enable the subscription, and refresh the subscription.
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | on        | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | on        | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (streaming = parallel);
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | parallel  | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | parallel  | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (streaming = false);
 ALTER SUBSCRIPTION regress_testsub SET (slot_name = NONE);
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 -- fail - publication already exists
@@ -314,10 +314,10 @@ ALTER SUBSCRIPTION regress_testsub ADD PUBLICATION testpub1, testpub2 WITH (refr
 ALTER SUBSCRIPTION regress_testsub ADD PUBLICATION testpub1, testpub2 WITH (refresh = false);
 ERROR:  publication "testpub1" is already in subscription "regress_testsub"
 \dRs+
-                                                                                                                        List of subscriptions
-      Name       |           Owner           | Enabled |         Publication         | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-----------------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub,testpub1,testpub2} | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                               List of subscriptions
+      Name       |           Owner           | Enabled |         Publication         | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-----------------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub,testpub1,testpub2} | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 -- fail - publication used more than once
@@ -332,10 +332,10 @@ ERROR:  publication "testpub3" is not in subscription "regress_testsub"
 -- ok - delete publications
 ALTER SUBSCRIPTION regress_testsub DROP PUBLICATION testpub1, testpub2 WITH (refresh = false);
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 DROP SUBSCRIPTION regress_testsub;
@@ -371,19 +371,19 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 WARNING:  subscription was created, but is not connected
 HINT:  To initiate replication, you must manually create the replication slot, enable the subscription, and refresh the subscription.
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | p                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | p                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 -- We can alter streaming when two_phase enabled
 ALTER SUBSCRIPTION regress_testsub SET (streaming = true);
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | on        | p                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | on        | p                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (slot_name = NONE);
@@ -393,10 +393,10 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 WARNING:  subscription was created, but is not connected
 HINT:  To initiate replication, you must manually create the replication slot, enable the subscription, and refresh the subscription.
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | on        | p                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | on        | p                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (slot_name = NONE);
@@ -409,18 +409,18 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 WARNING:  subscription was created, but is not connected
 HINT:  To initiate replication, you must manually create the replication slot, enable the subscription, and refresh the subscription.
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (disable_on_error = true);
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | t                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | t                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (slot_name = NONE);
diff --git a/src/test/subscription/t/099_twophase_added.pl b/src/test/subscription/t/099_twophase_added.pl
index 5a9a6c6476..662ecf308b 100644
--- a/src/test/subscription/t/099_twophase_added.pl
+++ b/src/test/subscription/t/099_twophase_added.pl
@@ -114,15 +114,38 @@ $result = $node_subscriber->safe_psql('postgres',
     "SELECT count(*) FROM pg_prepared_xacts;");
 is($result, q(1), "transaction has been prepared on subscriber");
 
-# Toggle the two_phase to "false" before the COMMIT PREPARED
-$node_subscriber->safe_psql(
-    'postgres', "
-    ALTER SUBSCRIPTION regress_sub DISABLE;
-    ALTER SUBSCRIPTION regress_sub SET (two_phase = false);
-    ALTER SUBSCRIPTION regress_sub ENABLE;");
+# Disable the subscription to alter the two_phase option
+$node_subscriber->safe_psql('postgres', "ALTER SUBSCRIPTION regress_sub DISABLE;");
+
+# Try altering the two_phase option to "false". The command will fail since
+# there is a prepared transaction and the 'force_alter' option is not specified
+# as true.
+my $stdout;
+my $stderr;
+
+($result, $stdout, $stderr) = $node_subscriber->psql(
+	'postgres', "ALTER SUBSCRIPTION regress_sub SET (two_phase = false);");
+ok($stderr =~ /cannot alter two_phase = false when there are prepared transactions/,
+	'ALTER SUBSCRIPTION failed');
+
+# Verify the prepared transaction still exists
+$result = $node_subscriber->safe_psql('postgres',
+    "SELECT count(*) FROM pg_prepared_xacts;");
+is($result, q(1), "prepared transaction still exists");
+
+$log_offset = -s $node_subscriber->logfile;
+
+# Alter the two_phase true to false with the force_alter option enabled. This
+# command will succeed after aborting the prepared transaction.
+$node_subscriber->safe_psql('postgres',
+    "ALTER SUBSCRIPTION regress_sub SET (two_phase = false, force_alter = true);");
+$node_subscriber->safe_psql('postgres', "ALTER SUBSCRIPTION regress_sub ENABLE;");
+
+# Verify the started worker recognized two_phase was disabled
+$node_subscriber->wait_for_log(
+	'logical replication apply worker for subscription "regress_sub" two_phase is DISABLED', $log_offset);
 
-# Verify any prepared transactions are aborted because two_phase is changed to
-# "false".
+# # Verify the prepared transaction was aborted
 $result = $node_subscriber->safe_psql('postgres',
     "SELECT count(*) FROM pg_prepared_xacts;");
 is($result, q(0), "prepared transaction done by worker is aborted");
-- 
2.43.0

From 5351d720e91921738cbc37a0dc01c1b75d183071 Mon Sep 17 00:00:00 2001
From: Ajin Cherian <ajinc@fast.au.fujitsu.com>
Date: Fri, 5 Apr 2024 06:47:18 -0400
Subject: [PATCH v12 1/4] Allow altering of two_phase option of a SUBSCRIPTION

This patch allows the user to alter the 'two_phase' option of a subscriber provided no
uncommitted prepared transactions are pending on that subscription.

Author: Cherian Ajin, Hayato Kuroda
---
 doc/src/sgml/ref/alter_subscription.sgml      | 12 ++--
 src/backend/access/transam/twophase.c         | 62 ++++++++++++++++
 src/backend/commands/subscriptioncmds.c       | 67 +++++++++++++----
 .../libpqwalreceiver/libpqwalreceiver.c       |  9 +--
 src/backend/replication/logical/launcher.c    | 22 ++++++
 src/backend/replication/logical/worker.c      | 21 +-----
 src/backend/replication/slot.c                | 18 ++++-
 src/backend/replication/walsender.c           | 18 ++++-
 src/bin/psql/tab-complete.c                   |  2 +-
 src/include/access/twophase.h                 |  5 ++
 src/include/replication/slot.h                |  3 +-
 src/include/replication/walreceiver.h         | 11 +--
 src/include/replication/worker_internal.h     |  1 +
 src/test/regress/expected/subscription.out    |  5 +-
 src/test/regress/sql/subscription.sql         |  5 +-
 src/test/subscription/t/021_twophase.pl       | 71 ++++++++++++++++++-
 16 files changed, 269 insertions(+), 63 deletions(-)

diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index 476f195622..0b23df1b77 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -68,8 +68,9 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
   <para>
    Commands <command>ALTER SUBSCRIPTION ... REFRESH PUBLICATION</command>,
    <command>ALTER SUBSCRIPTION ... {SET|ADD|DROP} PUBLICATION ...</command>
-   with <literal>refresh</literal> option as <literal>true</literal> and
-   <command>ALTER SUBSCRIPTION ... SET (failover = true|false)</command>
+   with <literal>refresh</literal> option as <literal>true</literal>,
+   <command>ALTER SUBSCRIPTION ... SET (failover = true|false)</command> and
+   <command>ALTER SUBSCRIPTION ... SET (two_phase = true|false)</command>
    cannot be executed inside a transaction block.
 
    These commands also cannot be executed when the subscription has
@@ -228,9 +229,12 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-disable-on-error"><literal>disable_on_error</literal></link>,
       <link linkend="sql-createsubscription-params-with-password-required"><literal>password_required</literal></link>,
       <link linkend="sql-createsubscription-params-with-run-as-owner"><literal>run_as_owner</literal></link>,
-      <link linkend="sql-createsubscription-params-with-origin"><literal>origin</literal></link>, and
-      <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>.
+      <link linkend="sql-createsubscription-params-with-origin"><literal>origin</literal></link>,
+      <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>, and
+      <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>.
       Only a superuser can set <literal>password_required = false</literal>.
+      The <literal>two_phase</literal> parameter can only be altered when the
+      subscription is disabled.
      </para>
 
      <para>
diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index 8090ac9fc1..66fa591eb5 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -2682,3 +2682,65 @@ LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 	LWLockRelease(TwoPhaseStateLock);
 	return found;
 }
+
+/*
+ * TwoPhaseTransactionGid
+ *		Form the prepared transaction GID for two_phase transactions.
+ *
+ * Return the GID in the supplied buffer.
+ */
+void
+TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid, int szgid)
+{
+	Assert(subid != InvalidRepOriginId);
+
+	if (!TransactionIdIsValid(xid))
+		ereport(ERROR,
+				(errcode(ERRCODE_PROTOCOL_VIOLATION),
+				 errmsg_internal("invalid two-phase transaction ID")));
+
+	snprintf(gid, szgid, "pg_gid_%u_%u", subid, xid);
+}
+
+/*
+ * IsTwoPhaseTransactionGidForSubid
+ *		Check whether the given GID (as formed by TwoPhaseTransactionGid) is
+ *		for the specified 'subid'.
+ */
+static bool
+IsTwoPhaseTransactionGidForSubid(Oid subid, char *gid)
+{
+	int				ret;
+	Oid				subid_written;
+	TransactionId	xid;
+
+	ret = sscanf(gid, "pg_gid_%u_%u", &subid_written, &xid);
+
+	return (ret == 2 && subid == subid_written);
+}
+
+/*
+ * LookupGXactBySubid
+ *		Check if the prepared transaction done by apply worker exists.
+ */
+bool
+LookupGXactBySubid(Oid subid)
+{
+	bool		found = false;
+
+	LWLockAcquire(TwoPhaseStateLock, LW_SHARED);
+	for (int i = 0; i < TwoPhaseState->numPrepXacts; i++)
+	{
+		GlobalTransaction gxact = TwoPhaseState->prepXacts[i];
+
+		/* Ignore not-yet-valid GIDs. */
+		if (gxact->valid &&
+			IsTwoPhaseTransactionGidForSubid(subid, gxact->gid))
+		{
+			found = true;
+			break;
+		}
+	}
+	LWLockRelease(TwoPhaseStateLock);
+	return found;
+}
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index e407428dbc..90d967eb7c 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -16,6 +16,7 @@
 
 #include "access/htup_details.h"
 #include "access/table.h"
+#include "access/twophase.h"
 #include "access/xact.h"
 #include "catalog/catalog.h"
 #include "catalog/dependency.h"
@@ -1143,7 +1144,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 			{
 				supported_opts = (SUBOPT_SLOT_NAME |
 								  SUBOPT_SYNCHRONOUS_COMMIT | SUBOPT_BINARY |
-								  SUBOPT_STREAMING | SUBOPT_DISABLE_ON_ERR |
+								  SUBOPT_STREAMING | SUBOPT_TWOPHASE_COMMIT |
+								  SUBOPT_DISABLE_ON_ERR |
 								  SUBOPT_PASSWORD_REQUIRED |
 								  SUBOPT_RUN_AS_OWNER | SUBOPT_FAILOVER |
 								  SUBOPT_ORIGIN);
@@ -1151,6 +1153,52 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 				parse_subscription_options(pstate, stmt->options,
 										   supported_opts, &opts);
 
+				if (IsSet(opts.specified_opts, SUBOPT_TWOPHASE_COMMIT))
+				{
+					/*
+					 * Do not allow changing the two_phase option if the
+					 * subscription is enabled. This is because the two_phase
+					 * option of the slot on the publisher cannot be modified
+					 * if the slot is currently acquired by the apply worker.
+					 */
+					if (form->subenabled)
+						ereport(ERROR,
+								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+								 errmsg("cannot set %s for enabled subscription",
+										"two_phase")));
+
+					/*
+					 * Stop all the subscription workers, just in case. Workers
+					 * may still survive even if the subscription is disabled.
+					 */
+					logicalrep_workers_stop(subid);
+
+					/*
+					 * two_phase cannot be disabled if there are any
+					 * uncommitted prepared transactions present.
+					 */
+					if (!opts.twophase &&
+						form->subtwophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
+						LookupGXactBySubid(subid))
+						ereport(ERROR,
+								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+								 errmsg("cannot disable two_phase when uncommitted prepared transactions present"),
+								 errhint("Resolve these transactions and try again")));
+
+					/*
+					 * The changed two_phase option of the slot can't be rolled
+					 * back.
+					 */
+					PreventInTransactionBlock(isTopLevel, "ALTER SUBSCRIPTION ... SET (two_phase)");
+
+					/* Change system catalog acoordingly */
+					values[Anum_pg_subscription_subtwophasestate - 1] =
+						CharGetDatum(opts.twophase ?
+									 LOGICALREP_TWOPHASE_STATE_PENDING :
+									 LOGICALREP_TWOPHASE_STATE_DISABLED);
+					replaces[Anum_pg_subscription_subtwophasestate - 1] = true;
+				}
+
 				if (IsSet(opts.specified_opts, SUBOPT_SLOT_NAME))
 				{
 					/*
@@ -1505,7 +1553,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 	 * doing the database operations we won't be able to rollback altered
 	 * slot.
 	 */
-	if (replaces[Anum_pg_subscription_subfailover - 1])
+	if (replaces[Anum_pg_subscription_subfailover - 1] ||
+		replaces[Anum_pg_subscription_subtwophasestate - 1])
 	{
 		bool		must_use_password;
 		char	   *err;
@@ -1525,7 +1574,7 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 
 		PG_TRY();
 		{
-			walrcv_alter_slot(wrconn, sub->slotname, opts.failover);
+			walrcv_alter_slot(wrconn, sub->slotname, opts.failover, opts.twophase);
 		}
 		PG_FINALLY();
 		{
@@ -1562,7 +1611,6 @@ DropSubscription(DropSubscriptionStmt *stmt, bool isTopLevel)
 	char	   *subname;
 	char	   *conninfo;
 	char	   *slotname;
-	List	   *subworkers;
 	ListCell   *lc;
 	char		originname[NAMEDATALEN];
 	char	   *err = NULL;
@@ -1672,16 +1720,7 @@ DropSubscription(DropSubscriptionStmt *stmt, bool isTopLevel)
 	 * New workers won't be started because we hold an exclusive lock on the
 	 * subscription till the end of the transaction.
 	 */
-	LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
-	subworkers = logicalrep_workers_find(subid, false);
-	LWLockRelease(LogicalRepWorkerLock);
-	foreach(lc, subworkers)
-	{
-		LogicalRepWorker *w = (LogicalRepWorker *) lfirst(lc);
-
-		logicalrep_worker_stop(w->subid, w->relid);
-	}
-	list_free(subworkers);
+	logicalrep_workers_stop(subid);
 
 	/*
 	 * Remove the no-longer-useful entry in the launcher's table of apply
diff --git a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
index 3c2b1bb496..998bbd517a 100644
--- a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
+++ b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
@@ -80,7 +80,7 @@ static char *libpqrcv_create_slot(WalReceiverConn *conn,
 								  CRSSnapshotAction snapshot_action,
 								  XLogRecPtr *lsn);
 static void libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-								bool failover);
+								bool failover, bool two_phase);
 static pid_t libpqrcv_get_backend_pid(WalReceiverConn *conn);
 static WalRcvExecResult *libpqrcv_exec(WalReceiverConn *conn,
 									   const char *query,
@@ -1121,15 +1121,16 @@ libpqrcv_create_slot(WalReceiverConn *conn, const char *slotname,
  */
 static void
 libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-					bool failover)
+					bool failover, bool two_phase)
 {
 	StringInfoData cmd;
 	PGresult   *res;
 
 	initStringInfo(&cmd);
-	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( FAILOVER %s )",
+	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( FAILOVER %s, TWO_PHASE %s )",
 					 quote_identifier(slotname),
-					 failover ? "true" : "false");
+					 failover ? "true" : "false",
+					 two_phase ? "true" : "false");
 
 	res = libpqrcv_PQexec(conn->streamConn, cmd.data);
 	pfree(cmd.data);
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 66070e9131..548f6e0edb 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -623,6 +623,28 @@ logicalrep_worker_stop(Oid subid, Oid relid)
 	LWLockRelease(LogicalRepWorkerLock);
 }
 
+/*
+ * Stop all the subscription workers.
+ */
+void
+logicalrep_workers_stop(Oid subid)
+{
+	List	   *subworkers;
+	ListCell   *lc;
+
+	LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
+	/* XXX clarify the reason why not only running workers are listed. */
+	subworkers = logicalrep_workers_find(subid, false);
+	LWLockRelease(LogicalRepWorkerLock);
+	foreach(lc, subworkers)
+	{
+		LogicalRepWorker *w = (LogicalRepWorker *) lfirst(lc);
+
+		logicalrep_worker_stop(w->subid, w->relid);
+	}
+	list_free(subworkers);
+}
+
 /*
  * Stop the given logical replication parallel apply worker.
  *
diff --git a/src/backend/replication/logical/worker.c b/src/backend/replication/logical/worker.c
index b5a80fe3e8..dcf656fd45 100644
--- a/src/backend/replication/logical/worker.c
+++ b/src/backend/replication/logical/worker.c
@@ -402,7 +402,6 @@ static void apply_handle_tuple_routing(ApplyExecutionData *edata,
 									   CmdType operation);
 
 /* Compute GID for two_phase transactions */
-static void TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid, int szgid);
 
 /* Functions for skipping changes */
 static void maybe_start_skipping_changes(XLogRecPtr finish_lsn);
@@ -3911,7 +3910,7 @@ maybe_reread_subscription(void)
 	/* !slotname should never happen when enabled is true. */
 	Assert(newsub->slotname);
 
-	/* two-phase should not be altered */
+	/* two-phase cannot be altered while the worker exists */
 	Assert(newsub->twophasestate == MySubscription->twophasestate);
 
 	/*
@@ -4396,24 +4395,6 @@ cleanup_subxact_info()
 	subxact_data.nsubxacts_max = 0;
 }
 
-/*
- * Form the prepared transaction GID for two_phase transactions.
- *
- * Return the GID in the supplied buffer.
- */
-static void
-TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid, int szgid)
-{
-	Assert(subid != InvalidRepOriginId);
-
-	if (!TransactionIdIsValid(xid))
-		ereport(ERROR,
-				(errcode(ERRCODE_PROTOCOL_VIOLATION),
-				 errmsg_internal("invalid two-phase transaction ID")));
-
-	snprintf(gid, szgid, "pg_gid_%u_%u", subid, xid);
-}
-
 /*
  * Common function to run the apply loop with error handling. Disable the
  * subscription, if necessary.
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index aa4ea387da..d0c8d5a4df 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -804,8 +804,10 @@ ReplicationSlotDrop(const char *name, bool nowait)
  * Change the definition of the slot identified by the specified name.
  */
 void
-ReplicationSlotAlter(const char *name, bool failover)
+ReplicationSlotAlter(const char *name, bool failover, bool two_phase)
 {
+	bool		update_slot = false;
+
 	Assert(MyReplicationSlot == NULL);
 
 	ReplicationSlotAcquire(name, false);
@@ -854,6 +856,20 @@ ReplicationSlotAlter(const char *name, bool failover)
 		MyReplicationSlot->data.failover = failover;
 		SpinLockRelease(&MyReplicationSlot->mutex);
 
+		update_slot = true;
+	}
+
+	if (MyReplicationSlot->data.two_phase != two_phase)
+	{
+		SpinLockAcquire(&MyReplicationSlot->mutex);
+		MyReplicationSlot->data.two_phase = two_phase;
+		SpinLockRelease(&MyReplicationSlot->mutex);
+
+		update_slot = true;
+	}
+
+	if (update_slot)
+	{
 		ReplicationSlotMarkDirty();
 		ReplicationSlotSave();
 	}
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index c623b07cf0..2e6ca35049 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1411,9 +1411,11 @@ DropReplicationSlot(DropReplicationSlotCmd *cmd)
  * Process extra options given to ALTER_REPLICATION_SLOT.
  */
 static void
-ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd, bool *failover)
+ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd,
+						  bool *failover, bool *two_phase)
 {
 	bool		failover_given = false;
+	bool		two_phase_given = false;
 
 	/* Parse options */
 	foreach_ptr(DefElem, defel, cmd->options)
@@ -1427,6 +1429,15 @@ ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd, bool *failover)
 			failover_given = true;
 			*failover = defGetBoolean(defel);
 		}
+		else if (strcmp(defel->defname, "two_phase") == 0)
+		{
+			if (two_phase_given)
+				ereport(ERROR,
+						(errcode(ERRCODE_SYNTAX_ERROR),
+						 errmsg("conflicting or redundant options")));
+			two_phase_given = true;
+			*two_phase = defGetBoolean(defel);
+		}
 		else
 			elog(ERROR, "unrecognized option: %s", defel->defname);
 	}
@@ -1439,9 +1450,10 @@ static void
 AlterReplicationSlot(AlterReplicationSlotCmd *cmd)
 {
 	bool		failover = false;
+	bool		two_phase = false;
 
-	ParseAlterReplSlotOptions(cmd, &failover);
-	ReplicationSlotAlter(cmd->slotname, failover);
+	ParseAlterReplSlotOptions(cmd, &failover, &two_phase);
+	ReplicationSlotAlter(cmd->slotname, failover, two_phase);
 }
 
 /*
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
index d453e224d9..891face1b6 100644
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -1948,7 +1948,7 @@ psql_completion(const char *text, int start, int end)
 	else if (HeadMatches("ALTER", "SUBSCRIPTION", MatchAny) && TailMatches("SET", "("))
 		COMPLETE_WITH("binary", "disable_on_error", "failover", "origin",
 					  "password_required", "run_as_owner", "slot_name",
-					  "streaming", "synchronous_commit");
+					  "streaming", "synchronous_commit", "two_phase");
 	/* ALTER SUBSCRIPTION <name> SKIP ( */
 	else if (HeadMatches("ALTER", "SUBSCRIPTION", MatchAny) && TailMatches("SKIP", "("))
 		COMPLETE_WITH("lsn");
diff --git a/src/include/access/twophase.h b/src/include/access/twophase.h
index 56248c0006..d37e06fdee 100644
--- a/src/include/access/twophase.h
+++ b/src/include/access/twophase.h
@@ -62,4 +62,9 @@ extern void PrepareRedoRemove(TransactionId xid, bool giveWarning);
 extern void restoreTwoPhaseData(void);
 extern bool LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 						TimestampTz origin_prepare_timestamp);
+
+extern void TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid,
+								   int szgid);
+extern bool LookupGXactBySubid(Oid subid);
+
 #endif							/* TWOPHASE_H */
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 1bc80960ef..014e216cf5 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -243,7 +243,8 @@ extern void ReplicationSlotCreate(const char *name, bool db_specific,
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
 extern void ReplicationSlotDropAcquired(void);
-extern void ReplicationSlotAlter(const char *name, bool failover);
+extern void ReplicationSlotAlter(const char *name, bool failover,
+								 bool two_phase);
 
 extern void ReplicationSlotAcquire(const char *name, bool nowait);
 extern void ReplicationSlotRelease(void);
diff --git a/src/include/replication/walreceiver.h b/src/include/replication/walreceiver.h
index 12f71fa99b..31fa1257ec 100644
--- a/src/include/replication/walreceiver.h
+++ b/src/include/replication/walreceiver.h
@@ -372,12 +372,13 @@ typedef char *(*walrcv_create_slot_fn) (WalReceiverConn *conn,
 /*
  * walrcv_alter_slot_fn
  *
- * Change the definition of a replication slot. Currently, it only supports
- * changing the failover property of the slot.
+ * Change the definition of a replication slot. Currently, it supports
+ * changing the failover and the two_phase property of the slot.
  */
 typedef void (*walrcv_alter_slot_fn) (WalReceiverConn *conn,
 									  const char *slotname,
-									  bool failover);
+									  bool failover,
+									  bool two_phase);
 
 /*
  * walrcv_get_backend_pid_fn
@@ -455,8 +456,8 @@ extern PGDLLIMPORT WalReceiverFunctionsType *WalReceiverFunctions;
 	WalReceiverFunctions->walrcv_send(conn, buffer, nbytes)
 #define walrcv_create_slot(conn, slotname, temporary, two_phase, failover, snapshot_action, lsn) \
 	WalReceiverFunctions->walrcv_create_slot(conn, slotname, temporary, two_phase, failover, snapshot_action, lsn)
-#define walrcv_alter_slot(conn, slotname, failover) \
-	WalReceiverFunctions->walrcv_alter_slot(conn, slotname, failover)
+#define walrcv_alter_slot(conn, slotname, failover, two_phase) \
+	WalReceiverFunctions->walrcv_alter_slot(conn, slotname, failover, two_phase)
 #define walrcv_get_backend_pid(conn) \
 	WalReceiverFunctions->walrcv_get_backend_pid(conn)
 #define walrcv_exec(conn, exec, nRetTypes, retTypes) \
diff --git a/src/include/replication/worker_internal.h b/src/include/replication/worker_internal.h
index 515aefd519..d5428263c1 100644
--- a/src/include/replication/worker_internal.h
+++ b/src/include/replication/worker_internal.h
@@ -246,6 +246,7 @@ extern bool logicalrep_worker_launch(LogicalRepWorkerType wtype,
 									 Oid userid, Oid relid,
 									 dsm_handle subworker_dsm);
 extern void logicalrep_worker_stop(Oid subid, Oid relid);
+extern void logicalrep_workers_stop(Oid subid);
 extern void logicalrep_pa_worker_stop(ParallelApplyWorkerInfo *winfo);
 extern void logicalrep_worker_wakeup(Oid subid, Oid relid);
 extern void logicalrep_worker_wakeup_ptr(LogicalRepWorker *worker);
diff --git a/src/test/regress/expected/subscription.out b/src/test/regress/expected/subscription.out
index 0f2a25cdc1..51fa4b9690 100644
--- a/src/test/regress/expected/subscription.out
+++ b/src/test/regress/expected/subscription.out
@@ -377,10 +377,7 @@ HINT:  To initiate replication, you must manually create the replication slot, e
  regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | p                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
---fail - alter of two_phase option not supported.
-ALTER SUBSCRIPTION regress_testsub SET (two_phase = false);
-ERROR:  unrecognized subscription parameter: "two_phase"
--- but can alter streaming when two_phase enabled
+-- We can alter streaming when two_phase enabled
 ALTER SUBSCRIPTION regress_testsub SET (streaming = true);
 \dRs+
                                                                                                                 List of subscriptions
diff --git a/src/test/regress/sql/subscription.sql b/src/test/regress/sql/subscription.sql
index 3e5ba4cb8c..a3886d79ca 100644
--- a/src/test/regress/sql/subscription.sql
+++ b/src/test/regress/sql/subscription.sql
@@ -256,10 +256,7 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUBLICATION testpub WITH (connect = false, two_phase = true);
 
 \dRs+
---fail - alter of two_phase option not supported.
-ALTER SUBSCRIPTION regress_testsub SET (two_phase = false);
-
--- but can alter streaming when two_phase enabled
+-- We can alter streaming when two_phase enabled
 ALTER SUBSCRIPTION regress_testsub SET (streaming = true);
 
 \dRs+
diff --git a/src/test/subscription/t/021_twophase.pl b/src/test/subscription/t/021_twophase.pl
index 9437cd4c3b..72df258000 100644
--- a/src/test/subscription/t/021_twophase.pl
+++ b/src/test/subscription/t/021_twophase.pl
@@ -367,6 +367,75 @@ $result =
   $node_subscriber->safe_psql('postgres', "SELECT count(*) FROM tab_copy;");
 is($result, qq(2), 'replicated data in subscriber table');
 
+# Clean up
+$node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub");
+
+###############################
+# Disable the subscription and alter it to two_phase = false,
+# then verify that the altered subscription reflects the two_phase option.
+###############################
+
+# Alter subscription two_phase to false
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy DISABLE");
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = false)");
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy ENABLE");
+
+# Wait for subscription startup
+$node_subscriber->wait_for_subscription_sync($node_publisher, $appname_copy);
+
+# Make sure that the two-phase is disabled on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+       "SELECT subtwophasestate FROM pg_subscription WHERE subname = 'tap_sub_copy';"
+);
+is($result, qq(d), 'two-phase should be disabled');
+
+# Now do a prepare on the publisher and make sure that it is not replicated.
+$node_publisher->safe_psql(
+       'postgres', qq{
+    BEGIN;
+    INSERT INTO tab_copy VALUES (100);
+    PREPARE TRANSACTION 'newgid';
+	});
+
+# Wait for the subscriber to catchup
+$node_publisher->wait_for_catchup($appname_copy);
+
+# Make sure there are no prepared transactions on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT count(*) FROM pg_prepared_xacts;");
+is($result, qq(0), 'should be no prepared transactions on subscriber');
+
+# Now commit the insert and verify that it IS replicated
+$node_publisher->safe_psql('postgres', "COMMIT PREPARED 'newgid';");
+
+# Wait for the subscriber to catchup
+$node_publisher->wait_for_catchup($appname_copy);
+
+# Make sure that the committed transaction is replicated.
+$result =
+	$node_subscriber->safe_psql('postgres', "SELECT count(*) FROM tab_copy;");
+is($result, qq(3), 'replicated data in subscriber table');
+
+# Alter subscription two_phase to true
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy DISABLE");
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = true)");
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy ENABLE");
+
+# Wait for subscription startup
+$node_subscriber->wait_for_subscription_sync($node_publisher, $appname_copy);
+
+# Make sure that the two-phase is enabled on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT subtwophasestate FROM pg_subscription WHERE subname = 'tap_sub_copy';"
+);
+is($result, qq(e), 'two-phase should be enabled');
+
 $node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub_copy;");
 $node_publisher->safe_psql('postgres', "DROP PUBLICATION tap_pub_copy;");
 
@@ -374,8 +443,6 @@ $node_publisher->safe_psql('postgres', "DROP PUBLICATION tap_pub_copy;");
 # check all the cleanup
 ###############################
 
-$node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub");
-
 $result = $node_subscriber->safe_psql('postgres',
 	"SELECT count(*) FROM pg_subscription");
 is($result, qq(0), 'check subscription was dropped on subscriber');
-- 
2.43.0

From b9eeaee48f2026a31e50a42c0ee869c065c3639d Mon Sep 17 00:00:00 2001
From: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Date: Wed, 17 Apr 2024 06:18:23 +0000
Subject: [PATCH v12 2/4] Alter slot option two_phase only when altering "true"
 to "false"
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Since the two_phase option is controlled by both the publisher (as a slot option)
and the subscriber (as a subscription option), the slot option must also be
modified.

Regarding the false->true case, the backend process alters the subtwophase to
LOGICALREP_TWOPHASE_STATE_PENDING once. After the subscription is enabled, a new
logical replication worker requests to change the two_phase option of its slot
from pending to true after the initial data synchronization is done. The code
path is the same as the case in which two_phase is initially set to true, so
there is no need to do something remarkable. However, for the true->false case,
the backend must connect to the publisher and expressly change the parameter
because the apply worker does not alter the option to false. Because this
operation cannot be rolled back, altering the two_phase parameter from "true"
to "false" within a transaction is prohibited.
---
 doc/src/sgml/ref/alter_subscription.sgml      |  2 +-
 src/backend/commands/subscriptioncmds.c       | 42 ++++++--
 .../libpqwalreceiver/libpqwalreceiver.c       | 23 +++--
 src/include/replication/walreceiver.h         |  5 +-
 src/test/subscription/meson.build             |  1 +
 src/test/subscription/t/099_twophase_added.pl | 96 +++++++++++++++++++
 6 files changed, 153 insertions(+), 16 deletions(-)
 create mode 100644 src/test/subscription/t/099_twophase_added.pl

diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index 0b23df1b77..475a42a2e3 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -70,7 +70,7 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
    <command>ALTER SUBSCRIPTION ... {SET|ADD|DROP} PUBLICATION ...</command>
    with <literal>refresh</literal> option as <literal>true</literal>,
    <command>ALTER SUBSCRIPTION ... SET (failover = true|false)</command> and
-   <command>ALTER SUBSCRIPTION ... SET (two_phase = true|false)</command>
+   <command>ALTER SUBSCRIPTION ... SET (two_phase = off)</command>
    cannot be executed inside a transaction block.
 
    These commands also cannot be executed when the subscription has
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index 90d967eb7c..ff733e3810 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -1097,6 +1097,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 	Form_pg_subscription form;
 	bits32		supported_opts;
 	SubOpts		opts = {0};
+	bool		update_failover;
+	bool		update_two_phase;
 
 	rel = table_open(SubscriptionRelationId, RowExclusiveLock);
 
@@ -1186,10 +1188,24 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 								 errhint("Resolve these transactions and try again")));
 
 					/*
-					 * The changed two_phase option of the slot can't be rolled
-					 * back.
+					 * Altering the parameter from "true" to "false" within a
+					 * transaction is prohibited. Since the apply worker does
+					 * not alter the slot option to false, the backend must
+					 * connect to the publisher and expressly change the
+					 * parameter.
+					 *
+					 * There is no need to do something remarkable regarding
+					 * the "false" to "true" case; the backend process alters
+					 * subtwophase to LOGICALREP_TWOPHASE_STATE_PENDING once.
+					 * After the subscription is enabled, a new logical
+					 * replication worker requests to change the two_phase
+					 * option of its slot from pending to true when the initial
+					 * data synchronization is done. The code path is the same
+					 * as the case in which two_phase is initially set to true.
 					 */
-					PreventInTransactionBlock(isTopLevel, "ALTER SUBSCRIPTION ... SET (two_phase)");
+					if (!opts.twophase)
+						PreventInTransactionBlock(isTopLevel,
+												  "ALTER SUBSCRIPTION ... SET (two_phase = false)");
 
 					/* Change system catalog acoordingly */
 					values[Anum_pg_subscription_subtwophasestate - 1] =
@@ -1547,14 +1563,24 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 	}
 
 	/*
-	 * Try to acquire the connection necessary for altering slot.
+	 * Check the need to alter the replication slot. Failover and two_phase
+	 * options are controlled by both the publisher (as a slot option) and the
+	 * subscriber (as a subscription option). The slot option must be altered
+	 * only when changing "true" to "false". The reason has already been
+	 * described in the ALTER_SUBSCRIPTION_OPTIONS section of this function.
+	 */
+	update_failover = replaces[Anum_pg_subscription_subfailover - 1];
+	update_two_phase = (replaces[Anum_pg_subscription_subtwophasestate - 1] &&
+						!opts.twophase);
+
+	/*
+	 * Try to acquire the connection necessary for altering slot, if needed.
 	 *
 	 * This has to be at the end because otherwise if there is an error while
 	 * doing the database operations we won't be able to rollback altered
 	 * slot.
 	 */
-	if (replaces[Anum_pg_subscription_subfailover - 1] ||
-		replaces[Anum_pg_subscription_subtwophasestate - 1])
+	if (update_failover || update_two_phase)
 	{
 		bool		must_use_password;
 		char	   *err;
@@ -1574,7 +1600,9 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 
 		PG_TRY();
 		{
-			walrcv_alter_slot(wrconn, sub->slotname, opts.failover, opts.twophase);
+			walrcv_alter_slot(wrconn, sub->slotname,
+							  update_failover ? &opts.failover : NULL,
+							  update_two_phase ? &opts.twophase : NULL);
 		}
 		PG_FINALLY();
 		{
diff --git a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
index 998bbd517a..ff013aa987 100644
--- a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
+++ b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
@@ -80,7 +80,7 @@ static char *libpqrcv_create_slot(WalReceiverConn *conn,
 								  CRSSnapshotAction snapshot_action,
 								  XLogRecPtr *lsn);
 static void libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-								bool failover, bool two_phase);
+								const bool *failover, const bool *two_phase);
 static pid_t libpqrcv_get_backend_pid(WalReceiverConn *conn);
 static WalRcvExecResult *libpqrcv_exec(WalReceiverConn *conn,
 									   const char *query,
@@ -1121,16 +1121,27 @@ libpqrcv_create_slot(WalReceiverConn *conn, const char *slotname,
  */
 static void
 libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-					bool failover, bool two_phase)
+					const bool *failover, const bool *two_phase)
 {
 	StringInfoData cmd;
 	PGresult   *res;
 
 	initStringInfo(&cmd);
-	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( FAILOVER %s, TWO_PHASE %s )",
-					 quote_identifier(slotname),
-					 failover ? "true" : "false",
-					 two_phase ? "true" : "false");
+	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( ",
+					 quote_identifier(slotname));
+
+	if (failover)
+		appendStringInfo(&cmd, "FAILOVER %s",
+						 *failover ? "true" : "false");
+
+	if (failover && two_phase)
+		appendStringInfo(&cmd, ", ");
+
+	if (two_phase)
+		appendStringInfo(&cmd, "TWO_PHASE %s",
+						 *two_phase ? "true" : "false");
+
+	appendStringInfoString(&cmd, " );");
 
 	res = libpqrcv_PQexec(conn->streamConn, cmd.data);
 	pfree(cmd.data);
diff --git a/src/include/replication/walreceiver.h b/src/include/replication/walreceiver.h
index 31fa1257ec..7ffa5a58b3 100644
--- a/src/include/replication/walreceiver.h
+++ b/src/include/replication/walreceiver.h
@@ -377,8 +377,9 @@ typedef char *(*walrcv_create_slot_fn) (WalReceiverConn *conn,
  */
 typedef void (*walrcv_alter_slot_fn) (WalReceiverConn *conn,
 									  const char *slotname,
-									  bool failover,
-									  bool two_phase);
+									  const bool *failover,
+									  const bool *two_phase);
+
 
 /*
  * walrcv_get_backend_pid_fn
diff --git a/src/test/subscription/meson.build b/src/test/subscription/meson.build
index c591cd7d61..b4bd522c3d 100644
--- a/src/test/subscription/meson.build
+++ b/src/test/subscription/meson.build
@@ -40,6 +40,7 @@ tests += {
       't/031_column_list.pl',
       't/032_subscribe_use_index.pl',
       't/033_run_as_table_owner.pl',
+      't/099_twophase_added.pl',
       't/100_bugs.pl',
     ],
   },
diff --git a/src/test/subscription/t/099_twophase_added.pl b/src/test/subscription/t/099_twophase_added.pl
new file mode 100644
index 0000000000..ac08969b32
--- /dev/null
+++ b/src/test/subscription/t/099_twophase_added.pl
@@ -0,0 +1,96 @@
+# Copyright (c) 2024, PostgreSQL Global Development Group
+
+# Additional tests for altering two_phase option
+use strict;
+use warnings FATAL => 'all';
+use PostgreSQL::Test::Cluster;
+use PostgreSQL::Test::Utils;
+use Test::More;
+
+# Initialize publisher node
+my $node_publisher = PostgreSQL::Test::Cluster->new('publisher');
+$node_publisher->init(allows_streaming => 'logical');
+$node_publisher->append_conf('postgresql.conf',
+	qq(max_prepared_transactions = 10));
+$node_publisher->start;
+
+# Create subscriber node
+my $node_subscriber = PostgreSQL::Test::Cluster->new('subscriber');
+$node_subscriber->init;
+$node_subscriber->append_conf('postgresql.conf',
+	qq(max_prepared_transactions = 10
+	log_min_messages = debug1));
+$node_subscriber->start;
+
+# Define tables on both nodes
+$node_publisher->safe_psql('postgres',
+    "CREATE TABLE tab_full (a int PRIMARY KEY);");
+$node_subscriber->safe_psql('postgres',
+	"CREATE TABLE tab_full (a int PRIMARY KEY)");
+
+# Setup logical replication, with two_phase = "false"
+my $publisher_connstr = $node_publisher->connstr . ' dbname=postgres';
+$node_publisher->safe_psql('postgres',
+	"CREATE PUBLICATION pub FOR ALL TABLES");
+
+my $log_offset = -s $node_subscriber->logfile;
+
+$node_subscriber->safe_psql(
+	'postgres', "
+	CREATE SUBSCRIPTION regress_sub
+	CONNECTION '$publisher_connstr' PUBLICATION pub
+	WITH (two_phase = false, copy_data = false, failover = false)");
+
+# Verify the started worker recognized two_phase was disabled
+$node_subscriber->wait_for_log(
+	'logical replication apply worker for subscription "regress_sub" two_phase is DISABLED', $log_offset);
+
+#####################
+# Check the case that prepared transactions exist on the publisher node.
+#
+# Since the two_phase is "false", then normally, this PREPARE will do nothing
+# until the COMMIT PREPARED, but in this test, we toggle the two_phase to
+# "true" again before the COMMIT PREPARED happens.
+
+# Prepare a transaction to insert some tuples into the table
+$node_publisher->safe_psql(
+	'postgres', "
+	BEGIN;
+	INSERT INTO tab_full VALUES (generate_series(1, 5));
+	PREPARE TRANSACTION 'test_prepared_tab_full';");
+
+$node_publisher->wait_for_catchup('regress_sub');
+
+# Verify the prepared transaction is not yet replicated to the subscriber
+# because two_phase is set to "false".
+my $result = $node_subscriber->safe_psql('postgres',
+    "SELECT count(*) FROM pg_prepared_xacts;");
+is($result, q(0), "transaction is not prepared on subscriber");
+
+$log_offset = -s $node_subscriber->logfile;
+
+# Toggle the two_phase to "true" *before* the COMMIT PREPARED. Since we are the
+# special path for the case where both two_phase and failover are altered, it
+# is also set to "true".
+$node_subscriber->safe_psql(
+    'postgres', "
+    ALTER SUBSCRIPTION regress_sub DISABLE;
+    ALTER SUBSCRIPTION regress_sub SET (two_phase = true, failover = true);
+    ALTER SUBSCRIPTION regress_sub ENABLE;");
+
+# Verify the started worker recognized two_phase was enabled
+$node_subscriber->wait_for_log(
+	'logical replication apply worker for subscription "regress_sub" two_phase is ENABLED', $log_offset);
+
+# And do COMMIT PREPARED the prepared transaction
+$node_publisher->safe_psql('postgres',
+    "COMMIT PREPARED 'test_prepared_tab_full';");
+$node_publisher->wait_for_catchup('regress_sub');
+
+# Verify inserted tuples are replicated
+$result = $node_subscriber->safe_psql('postgres',
+    "SELECT count(*) FROM tab_full;");
+is($result, q(5),
+   "prepared transactions done before altering can be replicated");
+
+done_testing();
-- 
2.43.0

From 9cbcac569f7eb28b15d9afc5645cfb97f9cd6164 Mon Sep 17 00:00:00 2001
From: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Date: Mon, 8 Apr 2024 12:39:12 +0000
Subject: [PATCH v12 3/4] Abort prepared transactions while altering two_phase
 to off

If we alter the two_phase parameter from "on" to "off" and there are prepared
transactions on the subscriber, they won't be resolved. To avoid this issue, we
allow the backend to abort all prepared transactions while altering the
subscription.
---
 doc/src/sgml/ref/alter_subscription.sgml      | 11 +++-
 src/backend/access/transam/twophase.c         | 17 ++---
 src/backend/commands/subscriptioncmds.c       | 65 +++++++++++--------
 src/include/access/twophase.h                 |  3 +-
 src/test/subscription/t/099_twophase_added.pl | 45 +++++++++++++
 5 files changed, 102 insertions(+), 39 deletions(-)

diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index 475a42a2e3..8801f37f0e 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -233,8 +233,6 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>, and
       <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>.
       Only a superuser can set <literal>password_required = false</literal>.
-      The <literal>two_phase</literal> parameter can only be altered when the
-      subscription is disabled.
      </para>
 
      <para>
@@ -256,6 +254,15 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>
       option is enabled.
      </para>
+
+     <para>
+      The <literal>two_phase</literal> parameter can only be altered when the
+      subscription is disabled. When altering the parameter from <literal>true</literal>
+      to <literal>false</literal>, the backend process checks for any incomplete
+      prepared transactions done by the logical replication worker (from when
+      <literal>two_phase</literal> parameter was still <literal>true</literal>)
+      and, if any are found, those are aborted.
+     </para>
     </listitem>
    </varlistentry>
 
diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index 66fa591eb5..f384bd8c0a 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -2720,13 +2720,13 @@ IsTwoPhaseTransactionGidForSubid(Oid subid, char *gid)
 }
 
 /*
- * LookupGXactBySubid
- *		Check if the prepared transaction done by apply worker exists.
+ * GetGidListBySubid
+ *      Get a list of GIDs which is PREPARE'd by the given subscription.
  */
-bool
-LookupGXactBySubid(Oid subid)
+List *
+GetGidListBySubid(Oid subid)
 {
-	bool		found = false;
+	List *list = NIL;
 
 	LWLockAcquire(TwoPhaseStateLock, LW_SHARED);
 	for (int i = 0; i < TwoPhaseState->numPrepXacts; i++)
@@ -2736,11 +2736,8 @@ LookupGXactBySubid(Oid subid)
 		/* Ignore not-yet-valid GIDs. */
 		if (gxact->valid &&
 			IsTwoPhaseTransactionGidForSubid(subid, gxact->gid))
-		{
-			found = true;
-			break;
-		}
+			list = lappend(list, pstrdup(gxact->gid));
 	}
 	LWLockRelease(TwoPhaseStateLock);
-	return found;
+	return list;
 }
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index ff733e3810..1c16d52673 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -1176,37 +1176,50 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 					logicalrep_workers_stop(subid);
 
 					/*
-					 * two_phase cannot be disabled if there are any
-					 * uncommitted prepared transactions present.
-					 */
-					if (!opts.twophase &&
-						form->subtwophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
-						LookupGXactBySubid(subid))
-						ereport(ERROR,
-								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-								 errmsg("cannot disable two_phase when uncommitted prepared transactions present"),
-								 errhint("Resolve these transactions and try again")));
-
-					/*
-					 * Altering the parameter from "true" to "false" within a
-					 * transaction is prohibited. Since the apply worker does
-					 * not alter the slot option to false, the backend must
-					 * connect to the publisher and expressly change the
-					 * parameter.
-					 *
-					 * There is no need to do something remarkable regarding
-					 * the "false" to "true" case; the backend process alters
-					 * subtwophase to LOGICALREP_TWOPHASE_STATE_PENDING once.
-					 * After the subscription is enabled, a new logical
-					 * replication worker requests to change the two_phase
-					 * option of its slot from pending to true when the initial
-					 * data synchronization is done. The code path is the same
-					 * as the case in which two_phase is initially set to true.
+					 * If two_phase was previously enabled, there is a
+					 * possibility that transactions have already been
+					 * PREPARE'd. They must be checked and rolled back.
 					 */
 					if (!opts.twophase)
+					{
+						List *prepared_xacts;
+
+						/*
+						 * Altering the parameter from "true" to "false" within
+						 * a transaction is prohibited. Since the apply worker
+						 * does not alter the slot option to false, the backend
+						 * must connect to the publisher and expressly change
+						 * the parameter.
+						 *
+						 * There is no need to do something remarkable
+						 * regarding the "false" to "true" case; the backend
+						 * process alters subtwophase to
+						 * LOGICALREP_TWOPHASE_STATE_PENDING once. After the
+						 * subscription is enabled, a new logical replication
+						 * worker requests to change the two_phase option of
+						 * its slot from pending to true when the initial data
+						 * synchronization is done. The code path is the same
+						 * as the case in which two_phase is initially set to
+						 * true.
+						 */
 						PreventInTransactionBlock(isTopLevel,
 												  "ALTER SUBSCRIPTION ... SET (two_phase = false)");
 
+						/*
+						 * To prevent prepared transactions from being
+						 * isolated, they must manually be aborted.
+						 */
+						if (sub->twophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
+							(prepared_xacts = GetGidListBySubid(subid)) != NIL)
+						{
+							/* Abort all listed transactions */
+							foreach_ptr(char, gid, prepared_xacts)
+								FinishPreparedTransaction(gid, false);
+
+							list_free_deep(prepared_xacts);
+						}
+					}
+
 					/* Change system catalog acoordingly */
 					values[Anum_pg_subscription_subtwophasestate - 1] =
 						CharGetDatum(opts.twophase ?
diff --git a/src/include/access/twophase.h b/src/include/access/twophase.h
index d37e06fdee..f7a5cf0c12 100644
--- a/src/include/access/twophase.h
+++ b/src/include/access/twophase.h
@@ -18,6 +18,7 @@
 #include "access/xlogdefs.h"
 #include "datatype/timestamp.h"
 #include "storage/lock.h"
+#include "nodes/pg_list.h"
 
 /*
  * GlobalTransactionData is defined in twophase.c; other places have no
@@ -65,6 +66,6 @@ extern bool LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 
 extern void TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid,
 								   int szgid);
-extern bool LookupGXactBySubid(Oid subid);
+extern List *GetGidListBySubid(Oid subid);
 
 #endif							/* TWOPHASE_H */
diff --git a/src/test/subscription/t/099_twophase_added.pl b/src/test/subscription/t/099_twophase_added.pl
index ac08969b32..5a9a6c6476 100644
--- a/src/test/subscription/t/099_twophase_added.pl
+++ b/src/test/subscription/t/099_twophase_added.pl
@@ -93,4 +93,49 @@ $result = $node_subscriber->safe_psql('postgres',
 is($result, q(5),
    "prepared transactions done before altering can be replicated");
 
+#####################
+# Check the case that prepared transactions exist on the subscriber node
+#
+# If the two_phase is altering from "true" to "false" and there are prepared
+# transactions on the subscriber, they must be aborted. This test checks it.
+
+# Prepare a transaction to insert some tuples into the table
+$node_publisher->safe_psql(
+	'postgres', "
+	BEGIN;
+	INSERT INTO tab_full VALUES (generate_series(6, 10));
+	PREPARE TRANSACTION 'test_prepared_tab_full';");
+
+$node_publisher->wait_for_catchup('regress_sub');
+
+# Verify the prepared transaction has been replicated to the subscriber because
+# two_phase is set to "true".
+$result = $node_subscriber->safe_psql('postgres',
+    "SELECT count(*) FROM pg_prepared_xacts;");
+is($result, q(1), "transaction has been prepared on subscriber");
+
+# Toggle the two_phase to "false" before the COMMIT PREPARED
+$node_subscriber->safe_psql(
+    'postgres', "
+    ALTER SUBSCRIPTION regress_sub DISABLE;
+    ALTER SUBSCRIPTION regress_sub SET (two_phase = false);
+    ALTER SUBSCRIPTION regress_sub ENABLE;");
+
+# Verify any prepared transactions are aborted because two_phase is changed to
+# "false".
+$result = $node_subscriber->safe_psql('postgres',
+    "SELECT count(*) FROM pg_prepared_xacts;");
+is($result, q(0), "prepared transaction done by worker is aborted");
+
+# Do COMMIT PREPARED the prepared transaction
+$node_publisher->safe_psql( 'postgres',
+    "COMMIT PREPARED 'test_prepared_tab_full';");
+$node_publisher->wait_for_catchup('regress_sub');
+
+# Verify inserted tuples are replicated
+$result = $node_subscriber->safe_psql('postgres',
+    "SELECT count(10) FROM tab_full;");
+is($result, q(10),
+   "prepared transactions on publisher can be replicated");
+
 done_testing();
-- 
2.43.0

From f2f90480f0c72a83c421e847cce9524576b71a3c Mon Sep 17 00:00:00 2001
From: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Date: Fri, 19 Apr 2024 11:03:19 +0000
Subject: [PATCH v12 4/4] Add force_alter option for ALTER SUBSCRIPTION ... SET
 command

Previously, all prepared transactions on the standby were rolled back when
toggling two_phase from "true" to "false". However, this operation may not be
expected by users. To ensure users understand what happens, we added the
"force_alter" parameter. When two_phase is toggling to "false", and there are
prepared transactions, they will be aborted only when "force_alter" is set to
true. Otherwise, an ERROR occurs.
---
 doc/src/sgml/catalogs.sgml                    |  12 ++
 doc/src/sgml/ref/alter_subscription.sgml      |  16 +-
 doc/src/sgml/ref/create_subscription.sgml     |  24 +++
 src/backend/catalog/pg_subscription.c         |   1 +
 src/backend/catalog/system_views.sql          |   2 +-
 src/backend/commands/subscriptioncmds.c       |  36 ++++-
 src/bin/pg_dump/pg_dump.c                     |  14 ++
 src/bin/pg_dump/pg_dump.h                     |   1 +
 src/bin/psql/describe.c                       |   7 +-
 src/include/catalog/pg_subscription.h         |  13 ++
 src/test/regress/expected/subscription.out    | 152 +++++++++---------
 src/test/subscription/t/099_twophase_added.pl |  39 ++++-
 12 files changed, 222 insertions(+), 95 deletions(-)

diff --git a/doc/src/sgml/catalogs.sgml b/doc/src/sgml/catalogs.sgml
index 15f6255d86..bab3dcbce4 100644
--- a/doc/src/sgml/catalogs.sgml
+++ b/doc/src/sgml/catalogs.sgml
@@ -8038,6 +8038,18 @@ SCRAM-SHA-256$<replaceable>&lt;iteration count&gt;</replaceable>:<replaceable>&l
       </para></entry>
      </row>
 
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>subforcealter</structfield> <type>bool</type>
+      </para>
+      <para>
+       If true, then the <link linkend="sql-altersubscription"><command>ALTER SUBSCRIPTION</command></link>
+       can sometimes be forced to proceed instead of giving an error. See
+       <link linkend="sql-createsubscription-params-with-force-alter"><literal>force_alter</literal></link>
+       parameter for details about when this might be useful.
+      </para></entry>
+     </row>
+
      <row>
       <entry role="catalog_table_entry"><para role="column_definition">
        <structfield>subconninfo</structfield> <type>text</type>
diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index 8801f37f0e..ab2cdaeaa3 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -230,8 +230,9 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-password-required"><literal>password_required</literal></link>,
       <link linkend="sql-createsubscription-params-with-run-as-owner"><literal>run_as_owner</literal></link>,
       <link linkend="sql-createsubscription-params-with-origin"><literal>origin</literal></link>,
-      <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>, and
-      <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>.
+      <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>,
+      <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>, and
+      <link linkend="sql-createsubscription-params-with-force-alter"><literal>force_alter</literal></link>
       Only a superuser can set <literal>password_required = false</literal>.
      </para>
 
@@ -257,11 +258,12 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
 
      <para>
       The <literal>two_phase</literal> parameter can only be altered when the
-      subscription is disabled. When altering the parameter from <literal>true</literal>
-      to <literal>false</literal>, the backend process checks for any incomplete
-      prepared transactions done by the logical replication worker (from when
-      <literal>two_phase</literal> parameter was still <literal>true</literal>)
-      and, if any are found, those are aborted.
+      subscription is disabled. Altering the parameter from <literal>true</literal>
+      to <literal>false</literal> will give an error when there are prepared
+      transactions done by the logical replication worker. If you want to alter
+      the parameter forcibly in this case,
+      <link linkend="sql-createsubscription-params-with-force-alter"><literal>force_alter</literal></link>
+      option must be set to <literal>true</literal>.
      </para>
     </listitem>
    </varlistentry>
diff --git a/doc/src/sgml/ref/create_subscription.sgml b/doc/src/sgml/ref/create_subscription.sgml
index 740b7d9421..83ac52f865 100644
--- a/doc/src/sgml/ref/create_subscription.sgml
+++ b/doc/src/sgml/ref/create_subscription.sgml
@@ -428,6 +428,30 @@ CREATE SUBSCRIPTION <replaceable class="parameter">subscription_name</replaceabl
          </para>
         </listitem>
        </varlistentry>
+
+       <varlistentry id="sql-createsubscription-params-with-force-alter">
+        <term><literal>force_alter</literal> (<type>boolean</type>)</term>
+        <listitem>
+         <para>
+          Specifies if the <link linkend="sql-altersubscription"><command>ALTER SUBSCRIPTION</command></link>
+          can be forced to proceed instead of giving an error.
+         </para>
+         <para>
+          There is currently only one scenario where this parameter has any
+          effect: When altering <literal>two_phase</literal> option from
+          <literal>true</literal> to <literal>false</literal> it is possible
+          for there to be incomplete prepared transactions done by the logical
+          replication worker (from when <literal>two_phase</literal> parameter
+          was still <literal>true</literal>). If <literal>force_alter</literal>
+          is <literal>false</literal>, then this will give an error; if
+          <literal>force_alter</literal> is <literal>true</literal>, then the
+          incomplete prepared transactions are aborted and the alter will proceed.
+         </para>
+         <para>
+          The default is <literal>false</literal>.
+         </para>
+        </listitem>
+       </varlistentry>
       </variablelist></para>
 
     </listitem>
diff --git a/src/backend/catalog/pg_subscription.c b/src/backend/catalog/pg_subscription.c
index 9efc9159f2..b568fe3470 100644
--- a/src/backend/catalog/pg_subscription.c
+++ b/src/backend/catalog/pg_subscription.c
@@ -72,6 +72,7 @@ GetSubscription(Oid subid, bool missing_ok)
 	sub->passwordrequired = subform->subpasswordrequired;
 	sub->runasowner = subform->subrunasowner;
 	sub->failover = subform->subfailover;
+	sub->forcealter = subform->subforcealter;
 
 	/* Get conninfo */
 	datum = SysCacheGetAttrNotNull(SUBSCRIPTIONOID,
diff --git a/src/backend/catalog/system_views.sql b/src/backend/catalog/system_views.sql
index 53047cab5f..de3d3d8f3e 100644
--- a/src/backend/catalog/system_views.sql
+++ b/src/backend/catalog/system_views.sql
@@ -1358,7 +1358,7 @@ REVOKE ALL ON pg_replication_origin_status FROM public;
 REVOKE ALL ON pg_subscription FROM public;
 GRANT SELECT (oid, subdbid, subskiplsn, subname, subowner, subenabled,
               subbinary, substream, subtwophasestate, subdisableonerr,
-			  subpasswordrequired, subrunasowner, subfailover,
+			  subpasswordrequired, subrunasowner, subfailover, subforcealter,
               subslotname, subsynccommit, subpublications, suborigin)
     ON pg_subscription TO public;
 
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index 1c16d52673..82177c8a49 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -73,6 +73,7 @@
 #define SUBOPT_FAILOVER				0x00002000
 #define SUBOPT_LSN					0x00004000
 #define SUBOPT_ORIGIN				0x00008000
+#define SUBOPT_FORCE_ALTER			0x00010000
 
 /* check if the 'val' has 'bits' set */
 #define IsSet(val, bits)  (((val) & (bits)) == (bits))
@@ -100,6 +101,7 @@ typedef struct SubOpts
 	bool		failover;
 	char	   *origin;
 	XLogRecPtr	lsn;
+	bool		force_alter;
 } SubOpts;
 
 static List *fetch_table_list(WalReceiverConn *wrconn, List *publications);
@@ -162,6 +164,8 @@ parse_subscription_options(ParseState *pstate, List *stmt_options,
 		opts->failover = false;
 	if (IsSet(supported_opts, SUBOPT_ORIGIN))
 		opts->origin = pstrdup(LOGICALREP_ORIGIN_ANY);
+	if (IsSet(supported_opts, SUBOPT_FORCE_ALTER))
+		opts->force_alter = false;
 
 	/* Parse options */
 	foreach(lc, stmt_options)
@@ -367,6 +371,15 @@ parse_subscription_options(ParseState *pstate, List *stmt_options,
 			opts->specified_opts |= SUBOPT_LSN;
 			opts->lsn = lsn;
 		}
+		else if (IsSet(supported_opts, SUBOPT_FORCE_ALTER) &&
+				 strcmp(defel->defname, "force_alter") == 0)
+		{
+			if (IsSet(opts->specified_opts, SUBOPT_FORCE_ALTER))
+				errorConflictingDefElem(defel, pstate);
+
+			opts->specified_opts |= SUBOPT_FORCE_ALTER;
+			opts->force_alter = defGetBoolean(defel);
+		}
 		else
 			ereport(ERROR,
 					(errcode(ERRCODE_SYNTAX_ERROR),
@@ -604,7 +617,8 @@ CreateSubscription(ParseState *pstate, CreateSubscriptionStmt *stmt,
 					  SUBOPT_SYNCHRONOUS_COMMIT | SUBOPT_BINARY |
 					  SUBOPT_STREAMING | SUBOPT_TWOPHASE_COMMIT |
 					  SUBOPT_DISABLE_ON_ERR | SUBOPT_PASSWORD_REQUIRED |
-					  SUBOPT_RUN_AS_OWNER | SUBOPT_FAILOVER | SUBOPT_ORIGIN);
+					  SUBOPT_RUN_AS_OWNER | SUBOPT_FAILOVER | SUBOPT_ORIGIN |
+					  SUBOPT_FORCE_ALTER);
 	parse_subscription_options(pstate, stmt->options, supported_opts, &opts);
 
 	/*
@@ -711,6 +725,7 @@ CreateSubscription(ParseState *pstate, CreateSubscriptionStmt *stmt,
 	values[Anum_pg_subscription_subpasswordrequired - 1] = BoolGetDatum(opts.passwordrequired);
 	values[Anum_pg_subscription_subrunasowner - 1] = BoolGetDatum(opts.runasowner);
 	values[Anum_pg_subscription_subfailover - 1] = BoolGetDatum(opts.failover);
+	values[Anum_pg_subscription_subforcealter - 1] = BoolGetDatum(opts.force_alter);
 	values[Anum_pg_subscription_subconninfo - 1] =
 		CStringGetTextDatum(conninfo);
 	if (opts.slot_name)
@@ -1150,7 +1165,7 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 								  SUBOPT_DISABLE_ON_ERR |
 								  SUBOPT_PASSWORD_REQUIRED |
 								  SUBOPT_RUN_AS_OWNER | SUBOPT_FAILOVER |
-								  SUBOPT_ORIGIN);
+								  SUBOPT_ORIGIN | SUBOPT_FORCE_ALTER);
 
 				parse_subscription_options(pstate, stmt->options,
 										   supported_opts, &opts);
@@ -1212,6 +1227,23 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 						if (sub->twophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
 							(prepared_xacts = GetGidListBySubid(subid)) != NIL)
 						{
+							bool raise_error =
+								IsSet(opts.specified_opts, SUBOPT_FORCE_ALTER) ?
+									!opts.force_alter : !sub->forcealter;
+
+							/*
+							 * Abort prepared transactions only if
+							 * 'force_alter' option is true. Otherwise raise
+							 * an ERROR.
+							 */
+							if (raise_error)
+								ereport(ERROR,
+										(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+										 errmsg("cannot alter %s when there are prepared transactions",
+												"two_phase = false"),
+										 errhint("Resolve these transactions or set %s, and then try again.",
+												 "force_alter = true")));
+
 							/* Abort all listed transactions */
 							foreach_ptr(char, gid, prepared_xacts)
 								FinishPreparedTransaction(gid, false);
diff --git a/src/bin/pg_dump/pg_dump.c b/src/bin/pg_dump/pg_dump.c
index cb14fcafea..16a6a225ae 100644
--- a/src/bin/pg_dump/pg_dump.c
+++ b/src/bin/pg_dump/pg_dump.c
@@ -4739,6 +4739,7 @@ getSubscriptions(Archive *fout)
 	int			i_suboriginremotelsn;
 	int			i_subenabled;
 	int			i_subfailover;
+	int			i_subforcealter;
 	int			i,
 				ntups;
 
@@ -4816,6 +4817,13 @@ getSubscriptions(Archive *fout)
 		appendPQExpBuffer(query,
 						  " false AS subfailover\n");
 
+	if (fout->remoteVersion >= 170000)
+		appendPQExpBufferStr(query,
+							 " s.subforcealter\n");
+	else
+		appendPQExpBuffer(query,
+						  " false AS subforcealter\n");
+
 	appendPQExpBufferStr(query,
 						 "FROM pg_subscription s\n");
 
@@ -4854,6 +4862,7 @@ getSubscriptions(Archive *fout)
 	i_suboriginremotelsn = PQfnumber(res, "suboriginremotelsn");
 	i_subenabled = PQfnumber(res, "subenabled");
 	i_subfailover = PQfnumber(res, "subfailover");
+	i_subforcealter = PQfnumber(res, "subforcealter");
 
 	subinfo = pg_malloc(ntups * sizeof(SubscriptionInfo));
 
@@ -4900,6 +4909,8 @@ getSubscriptions(Archive *fout)
 			pg_strdup(PQgetvalue(res, i, i_subenabled));
 		subinfo[i].subfailover =
 			pg_strdup(PQgetvalue(res, i, i_subfailover));
+		subinfo[i].subforcealter =
+			pg_strdup(PQgetvalue(res, i, i_subforcealter));
 
 		/* Decide whether we want to dump it */
 		selectDumpableObject(&(subinfo[i].dobj), fout);
@@ -5140,6 +5151,9 @@ dumpSubscription(Archive *fout, const SubscriptionInfo *subinfo)
 	if (strcmp(subinfo->subfailover, "t") == 0)
 		appendPQExpBufferStr(query, ", failover = true");
 
+	if (strcmp(subinfo->subforcealter, "t") == 0)
+		appendPQExpBufferStr(query, ", force_alter = true");
+
 	if (strcmp(subinfo->subsynccommit, "off") != 0)
 		appendPQExpBuffer(query, ", synchronous_commit = %s", fmtId(subinfo->subsynccommit));
 
diff --git a/src/bin/pg_dump/pg_dump.h b/src/bin/pg_dump/pg_dump.h
index 865823868f..bb0fda3b29 100644
--- a/src/bin/pg_dump/pg_dump.h
+++ b/src/bin/pg_dump/pg_dump.h
@@ -671,6 +671,7 @@ typedef struct _SubscriptionInfo
 	char	   *suborigin;
 	char	   *suboriginremotelsn;
 	char	   *subfailover;
+	char	   *subforcealter;
 } SubscriptionInfo;
 
 /*
diff --git a/src/bin/psql/describe.c b/src/bin/psql/describe.c
index f67bf0b892..dba229a25d 100644
--- a/src/bin/psql/describe.c
+++ b/src/bin/psql/describe.c
@@ -6529,7 +6529,7 @@ describeSubscriptions(const char *pattern, bool verbose)
 	printQueryOpt myopt = pset.popt;
 	static const bool translate_columns[] = {false, false, false, false,
 		false, false, false, false, false, false, false, false, false, false,
-	false};
+	false, false};
 
 	if (pset.sversion < 100000)
 	{
@@ -6598,6 +6598,11 @@ describeSubscriptions(const char *pattern, bool verbose)
 							  ", subfailover AS \"%s\"\n",
 							  gettext_noop("Failover"));
 
+		if (pset.sversion >= 170000)
+			appendPQExpBuffer(&buf,
+							  ", subforcealter AS \"%s\"\n",
+							  gettext_noop("Force alter"));
+
 		appendPQExpBuffer(&buf,
 						  ",  subsynccommit AS \"%s\"\n"
 						  ",  subconninfo AS \"%s\"\n",
diff --git a/src/include/catalog/pg_subscription.h b/src/include/catalog/pg_subscription.h
index 0aa14ec4a2..c23de43d79 100644
--- a/src/include/catalog/pg_subscription.h
+++ b/src/include/catalog/pg_subscription.h
@@ -98,6 +98,13 @@ CATALOG(pg_subscription,6100,SubscriptionRelationId) BKI_SHARED_RELATION BKI_ROW
 								 * slots) in the upstream database are enabled
 								 * to be synchronized to the standbys. */
 
+	bool		subforcealter;	/* True allows the ALTER SUBSCRIPTION command
+								 * to proceed under conditions that would
+								 * otherwise result in an error. Currently,
+								 * 'force_alter' only has an effect when
+								 * altering the two_phase option from "true" to
+								 * "false". */
+
 #ifdef CATALOG_VARLEN			/* variable-length fields start here */
 	/* Connection string to the publisher */
 	text		subconninfo BKI_FORCE_NOT_NULL;
@@ -151,6 +158,12 @@ typedef struct Subscription
 								 * (i.e. the main slot and the table sync
 								 * slots) in the upstream database are enabled
 								 * to be synchronized to the standbys. */
+	bool		forcealter;		/* True allows the ALTER SUBSCRIPTION command
+								 * to proceed under conditions that would
+								 * otherwise result in an error. Currently,
+								 * 'force_alter' only has an effect when
+								 * altering the two_phase option from "true" to
+								 * "false". */
 	char	   *conninfo;		/* Connection string to the publisher */
 	char	   *slotname;		/* Name of the replication slot */
 	char	   *synccommit;		/* Synchronous commit setting for worker */
diff --git a/src/test/regress/expected/subscription.out b/src/test/regress/expected/subscription.out
index 51fa4b9690..b36fc6b8f7 100644
--- a/src/test/regress/expected/subscription.out
+++ b/src/test/regress/expected/subscription.out
@@ -116,18 +116,18 @@ CREATE SUBSCRIPTION regress_testsub4 CONNECTION 'dbname=regress_doesnotexist' PU
 WARNING:  subscription was created, but is not connected
 HINT:  To initiate replication, you must manually create the replication slot, enable the subscription, and refresh the subscription.
 \dRs+ regress_testsub4
-                                                                                                                 List of subscriptions
-       Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
-------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub4 | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | none   | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                        List of subscriptions
+       Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub4 | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | none   | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub4 SET (origin = any);
 \dRs+ regress_testsub4
-                                                                                                                 List of subscriptions
-       Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
-------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub4 | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                        List of subscriptions
+       Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub4 | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 DROP SUBSCRIPTION regress_testsub3;
@@ -145,10 +145,10 @@ ALTER SUBSCRIPTION regress_testsub CONNECTION 'foobar';
 ERROR:  invalid connection string syntax: missing "=" after "foobar" in connection info string
 
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET PUBLICATION testpub2, testpub3 WITH (refresh = false);
@@ -157,10 +157,10 @@ ALTER SUBSCRIPTION regress_testsub SET (slot_name = 'newname');
 ALTER SUBSCRIPTION regress_testsub SET (password_required = false);
 ALTER SUBSCRIPTION regress_testsub SET (run_as_owner = true);
 \dRs+
-                                                                                                                     List of subscriptions
-      Name       |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |           Conninfo           | Skip LSN 
------------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+------------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | f                 | t             | f        | off                | dbname=regress_doesnotexist2 | 0/0
+                                                                                                                            List of subscriptions
+      Name       |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |           Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+------------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | f                 | t             | f        | f           | off                | dbname=regress_doesnotexist2 | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (password_required = true);
@@ -176,10 +176,10 @@ ERROR:  unrecognized subscription parameter: "create_slot"
 -- ok
 ALTER SUBSCRIPTION regress_testsub SKIP (lsn = '0/12345');
 \dRs+
-                                                                                                                     List of subscriptions
-      Name       |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |           Conninfo           | Skip LSN 
------------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+------------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist2 | 0/12345
+                                                                                                                            List of subscriptions
+      Name       |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |           Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+------------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist2 | 0/12345
 (1 row)
 
 -- ok - with lsn = NONE
@@ -188,10 +188,10 @@ ALTER SUBSCRIPTION regress_testsub SKIP (lsn = NONE);
 ALTER SUBSCRIPTION regress_testsub SKIP (lsn = '0/0');
 ERROR:  invalid WAL location (LSN): 0/0
 \dRs+
-                                                                                                                     List of subscriptions
-      Name       |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |           Conninfo           | Skip LSN 
------------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+------------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist2 | 0/0
+                                                                                                                            List of subscriptions
+      Name       |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |           Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+------------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist2 | 0/0
 (1 row)
 
 BEGIN;
@@ -223,10 +223,10 @@ ALTER SUBSCRIPTION regress_testsub_foo SET (synchronous_commit = foobar);
 ERROR:  invalid value for parameter "synchronous_commit": "foobar"
 HINT:  Available values: local, remote_write, remote_apply, on, off.
 \dRs+
-                                                                                                                       List of subscriptions
-        Name         |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |           Conninfo           | Skip LSN 
----------------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+------------------------------+----------
- regress_testsub_foo | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | t                 | f             | f        | local              | dbname=regress_doesnotexist2 | 0/0
+                                                                                                                              List of subscriptions
+        Name         |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |           Conninfo           | Skip LSN 
+---------------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+------------------------------+----------
+ regress_testsub_foo | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | t                 | f             | f        | f           | local              | dbname=regress_doesnotexist2 | 0/0
 (1 row)
 
 -- rename back to keep the rest simple
@@ -255,19 +255,19 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 WARNING:  subscription was created, but is not connected
 HINT:  To initiate replication, you must manually create the replication slot, enable the subscription, and refresh the subscription.
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | t      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | t      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (binary = false);
 ALTER SUBSCRIPTION regress_testsub SET (slot_name = NONE);
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 DROP SUBSCRIPTION regress_testsub;
@@ -279,27 +279,27 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 WARNING:  subscription was created, but is not connected
 HINT:  To initiate replication, you must manually create the replication slot, enable the subscription, and refresh the subscription.
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | on        | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | on        | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (streaming = parallel);
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | parallel  | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | parallel  | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (streaming = false);
 ALTER SUBSCRIPTION regress_testsub SET (slot_name = NONE);
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 -- fail - publication already exists
@@ -314,10 +314,10 @@ ALTER SUBSCRIPTION regress_testsub ADD PUBLICATION testpub1, testpub2 WITH (refr
 ALTER SUBSCRIPTION regress_testsub ADD PUBLICATION testpub1, testpub2 WITH (refresh = false);
 ERROR:  publication "testpub1" is already in subscription "regress_testsub"
 \dRs+
-                                                                                                                        List of subscriptions
-      Name       |           Owner           | Enabled |         Publication         | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-----------------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub,testpub1,testpub2} | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                               List of subscriptions
+      Name       |           Owner           | Enabled |         Publication         | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-----------------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub,testpub1,testpub2} | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 -- fail - publication used more than once
@@ -332,10 +332,10 @@ ERROR:  publication "testpub3" is not in subscription "regress_testsub"
 -- ok - delete publications
 ALTER SUBSCRIPTION regress_testsub DROP PUBLICATION testpub1, testpub2 WITH (refresh = false);
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 DROP SUBSCRIPTION regress_testsub;
@@ -371,19 +371,19 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 WARNING:  subscription was created, but is not connected
 HINT:  To initiate replication, you must manually create the replication slot, enable the subscription, and refresh the subscription.
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | p                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | p                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 -- We can alter streaming when two_phase enabled
 ALTER SUBSCRIPTION regress_testsub SET (streaming = true);
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | on        | p                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | on        | p                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (slot_name = NONE);
@@ -393,10 +393,10 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 WARNING:  subscription was created, but is not connected
 HINT:  To initiate replication, you must manually create the replication slot, enable the subscription, and refresh the subscription.
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | on        | p                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | on        | p                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (slot_name = NONE);
@@ -409,18 +409,18 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 WARNING:  subscription was created, but is not connected
 HINT:  To initiate replication, you must manually create the replication slot, enable the subscription, and refresh the subscription.
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (disable_on_error = true);
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | t                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | t                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (slot_name = NONE);
diff --git a/src/test/subscription/t/099_twophase_added.pl b/src/test/subscription/t/099_twophase_added.pl
index 5a9a6c6476..662ecf308b 100644
--- a/src/test/subscription/t/099_twophase_added.pl
+++ b/src/test/subscription/t/099_twophase_added.pl
@@ -114,15 +114,38 @@ $result = $node_subscriber->safe_psql('postgres',
     "SELECT count(*) FROM pg_prepared_xacts;");
 is($result, q(1), "transaction has been prepared on subscriber");
 
-# Toggle the two_phase to "false" before the COMMIT PREPARED
-$node_subscriber->safe_psql(
-    'postgres', "
-    ALTER SUBSCRIPTION regress_sub DISABLE;
-    ALTER SUBSCRIPTION regress_sub SET (two_phase = false);
-    ALTER SUBSCRIPTION regress_sub ENABLE;");
+# Disable the subscription to alter the two_phase option
+$node_subscriber->safe_psql('postgres', "ALTER SUBSCRIPTION regress_sub DISABLE;");
+
+# Try altering the two_phase option to "false". The command will fail since
+# there is a prepared transaction and the 'force_alter' option is not specified
+# as true.
+my $stdout;
+my $stderr;
+
+($result, $stdout, $stderr) = $node_subscriber->psql(
+	'postgres', "ALTER SUBSCRIPTION regress_sub SET (two_phase = false);");
+ok($stderr =~ /cannot alter two_phase = false when there are prepared transactions/,
+	'ALTER SUBSCRIPTION failed');
+
+# Verify the prepared transaction still exists
+$result = $node_subscriber->safe_psql('postgres',
+    "SELECT count(*) FROM pg_prepared_xacts;");
+is($result, q(1), "prepared transaction still exists");
+
+$log_offset = -s $node_subscriber->logfile;
+
+# Alter the two_phase true to false with the force_alter option enabled. This
+# command will succeed after aborting the prepared transaction.
+$node_subscriber->safe_psql('postgres',
+    "ALTER SUBSCRIPTION regress_sub SET (two_phase = false, force_alter = true);");
+$node_subscriber->safe_psql('postgres', "ALTER SUBSCRIPTION regress_sub ENABLE;");
+
+# Verify the started worker recognized two_phase was disabled
+$node_subscriber->wait_for_log(
+	'logical replication apply worker for subscription "regress_sub" two_phase is DISABLED', $log_offset);
 
-# Verify any prepared transactions are aborted because two_phase is changed to
-# "false".
+# # Verify the prepared transaction was aborted
 $result = $node_subscriber->safe_psql('postgres',
     "SELECT count(*) FROM pg_prepared_xacts;");
 is($result, q(0), "prepared transaction done by worker is aborted");
-- 
2.43.0

From 40deb2d49d46b9682e6805fca5c27d119acf6c3e Mon Sep 17 00:00:00 2001
From: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Date: Fri, 19 Apr 2024 11:03:19 +0000
Subject: [PATCH v13 4/4] Add force_alter option for ALTER SUBSCRIPTION ... SET
 command

Previously, all prepared transactions on the standby were rolled back when
toggling two_phase from "true" to "false". However, this operation may not be
expected by users. To ensure users understand what happens, we added the
"force_alter" parameter. When two_phase is toggling to "false", and there are
prepared transactions, they will be aborted only when "force_alter" is set to
true. Otherwise, an ERROR occurs.
---
 doc/src/sgml/catalogs.sgml                    |  12 ++
 doc/src/sgml/ref/alter_subscription.sgml      |  16 +-
 doc/src/sgml/ref/create_subscription.sgml     |  24 +++
 src/backend/catalog/pg_subscription.c         |   1 +
 src/backend/catalog/system_views.sql          |   2 +-
 src/backend/commands/subscriptioncmds.c       |  36 ++++-
 src/bin/pg_dump/pg_dump.c                     |  18 ++-
 src/bin/pg_dump/pg_dump.h                     |   1 +
 src/bin/psql/describe.c                       |   7 +-
 src/include/catalog/pg_subscription.h         |  13 ++
 src/test/regress/expected/subscription.out    | 152 +++++++++---------
 src/test/subscription/t/099_twophase_added.pl |  44 ++++-
 12 files changed, 229 insertions(+), 97 deletions(-)

diff --git a/doc/src/sgml/catalogs.sgml b/doc/src/sgml/catalogs.sgml
index a63cc71efa..89b4fd07f1 100644
--- a/doc/src/sgml/catalogs.sgml
+++ b/doc/src/sgml/catalogs.sgml
@@ -8034,6 +8034,18 @@ SCRAM-SHA-256$<replaceable>&lt;iteration count&gt;</replaceable>:<replaceable>&l
       </para></entry>
      </row>
 
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>subforcealter</structfield> <type>bool</type>
+      </para>
+      <para>
+       If true, then the <link linkend="sql-altersubscription"><command>ALTER SUBSCRIPTION</command></link>
+       can sometimes be forced to proceed instead of giving an error. See
+       <link linkend="sql-createsubscription-params-with-force-alter"><literal>force_alter</literal></link>
+       parameter for details about when this might be useful.
+      </para></entry>
+     </row>
+
      <row>
       <entry role="catalog_table_entry"><para role="column_definition">
        <structfield>subconninfo</structfield> <type>text</type>
diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index 8801f37f0e..ab2cdaeaa3 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -230,8 +230,9 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-password-required"><literal>password_required</literal></link>,
       <link linkend="sql-createsubscription-params-with-run-as-owner"><literal>run_as_owner</literal></link>,
       <link linkend="sql-createsubscription-params-with-origin"><literal>origin</literal></link>,
-      <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>, and
-      <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>.
+      <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>,
+      <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>, and
+      <link linkend="sql-createsubscription-params-with-force-alter"><literal>force_alter</literal></link>
       Only a superuser can set <literal>password_required = false</literal>.
      </para>
 
@@ -257,11 +258,12 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
 
      <para>
       The <literal>two_phase</literal> parameter can only be altered when the
-      subscription is disabled. When altering the parameter from <literal>true</literal>
-      to <literal>false</literal>, the backend process checks for any incomplete
-      prepared transactions done by the logical replication worker (from when
-      <literal>two_phase</literal> parameter was still <literal>true</literal>)
-      and, if any are found, those are aborted.
+      subscription is disabled. Altering the parameter from <literal>true</literal>
+      to <literal>false</literal> will give an error when there are prepared
+      transactions done by the logical replication worker. If you want to alter
+      the parameter forcibly in this case,
+      <link linkend="sql-createsubscription-params-with-force-alter"><literal>force_alter</literal></link>
+      option must be set to <literal>true</literal>.
      </para>
     </listitem>
    </varlistentry>
diff --git a/doc/src/sgml/ref/create_subscription.sgml b/doc/src/sgml/ref/create_subscription.sgml
index 740b7d9421..83ac52f865 100644
--- a/doc/src/sgml/ref/create_subscription.sgml
+++ b/doc/src/sgml/ref/create_subscription.sgml
@@ -428,6 +428,30 @@ CREATE SUBSCRIPTION <replaceable class="parameter">subscription_name</replaceabl
          </para>
         </listitem>
        </varlistentry>
+
+       <varlistentry id="sql-createsubscription-params-with-force-alter">
+        <term><literal>force_alter</literal> (<type>boolean</type>)</term>
+        <listitem>
+         <para>
+          Specifies if the <link linkend="sql-altersubscription"><command>ALTER SUBSCRIPTION</command></link>
+          can be forced to proceed instead of giving an error.
+         </para>
+         <para>
+          There is currently only one scenario where this parameter has any
+          effect: When altering <literal>two_phase</literal> option from
+          <literal>true</literal> to <literal>false</literal> it is possible
+          for there to be incomplete prepared transactions done by the logical
+          replication worker (from when <literal>two_phase</literal> parameter
+          was still <literal>true</literal>). If <literal>force_alter</literal>
+          is <literal>false</literal>, then this will give an error; if
+          <literal>force_alter</literal> is <literal>true</literal>, then the
+          incomplete prepared transactions are aborted and the alter will proceed.
+         </para>
+         <para>
+          The default is <literal>false</literal>.
+         </para>
+        </listitem>
+       </varlistentry>
       </variablelist></para>
 
     </listitem>
diff --git a/src/backend/catalog/pg_subscription.c b/src/backend/catalog/pg_subscription.c
index 9efc9159f2..b568fe3470 100644
--- a/src/backend/catalog/pg_subscription.c
+++ b/src/backend/catalog/pg_subscription.c
@@ -72,6 +72,7 @@ GetSubscription(Oid subid, bool missing_ok)
 	sub->passwordrequired = subform->subpasswordrequired;
 	sub->runasowner = subform->subrunasowner;
 	sub->failover = subform->subfailover;
+	sub->forcealter = subform->subforcealter;
 
 	/* Get conninfo */
 	datum = SysCacheGetAttrNotNull(SUBSCRIPTIONOID,
diff --git a/src/backend/catalog/system_views.sql b/src/backend/catalog/system_views.sql
index efb29adeb3..3366da57fd 100644
--- a/src/backend/catalog/system_views.sql
+++ b/src/backend/catalog/system_views.sql
@@ -1359,7 +1359,7 @@ REVOKE ALL ON pg_replication_origin_status FROM public;
 REVOKE ALL ON pg_subscription FROM public;
 GRANT SELECT (oid, subdbid, subskiplsn, subname, subowner, subenabled,
               subbinary, substream, subtwophasestate, subdisableonerr,
-			  subpasswordrequired, subrunasowner, subfailover,
+			  subpasswordrequired, subrunasowner, subfailover, subforcealter,
               subslotname, subsynccommit, subpublications, suborigin)
     ON pg_subscription TO public;
 
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index 2532b40365..5ab5172a38 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -73,6 +73,7 @@
 #define SUBOPT_FAILOVER				0x00002000
 #define SUBOPT_LSN					0x00004000
 #define SUBOPT_ORIGIN				0x00008000
+#define SUBOPT_FORCE_ALTER			0x00010000
 
 /* check if the 'val' has 'bits' set */
 #define IsSet(val, bits)  (((val) & (bits)) == (bits))
@@ -100,6 +101,7 @@ typedef struct SubOpts
 	bool		failover;
 	char	   *origin;
 	XLogRecPtr	lsn;
+	bool		force_alter;
 } SubOpts;
 
 static List *fetch_table_list(WalReceiverConn *wrconn, List *publications);
@@ -162,6 +164,8 @@ parse_subscription_options(ParseState *pstate, List *stmt_options,
 		opts->failover = false;
 	if (IsSet(supported_opts, SUBOPT_ORIGIN))
 		opts->origin = pstrdup(LOGICALREP_ORIGIN_ANY);
+	if (IsSet(supported_opts, SUBOPT_FORCE_ALTER))
+		opts->force_alter = false;
 
 	/* Parse options */
 	foreach(lc, stmt_options)
@@ -367,6 +371,15 @@ parse_subscription_options(ParseState *pstate, List *stmt_options,
 			opts->specified_opts |= SUBOPT_LSN;
 			opts->lsn = lsn;
 		}
+		else if (IsSet(supported_opts, SUBOPT_FORCE_ALTER) &&
+				 strcmp(defel->defname, "force_alter") == 0)
+		{
+			if (IsSet(opts->specified_opts, SUBOPT_FORCE_ALTER))
+				errorConflictingDefElem(defel, pstate);
+
+			opts->specified_opts |= SUBOPT_FORCE_ALTER;
+			opts->force_alter = defGetBoolean(defel);
+		}
 		else
 			ereport(ERROR,
 					(errcode(ERRCODE_SYNTAX_ERROR),
@@ -604,7 +617,8 @@ CreateSubscription(ParseState *pstate, CreateSubscriptionStmt *stmt,
 					  SUBOPT_SYNCHRONOUS_COMMIT | SUBOPT_BINARY |
 					  SUBOPT_STREAMING | SUBOPT_TWOPHASE_COMMIT |
 					  SUBOPT_DISABLE_ON_ERR | SUBOPT_PASSWORD_REQUIRED |
-					  SUBOPT_RUN_AS_OWNER | SUBOPT_FAILOVER | SUBOPT_ORIGIN);
+					  SUBOPT_RUN_AS_OWNER | SUBOPT_FAILOVER | SUBOPT_ORIGIN |
+					  SUBOPT_FORCE_ALTER);
 	parse_subscription_options(pstate, stmt->options, supported_opts, &opts);
 
 	/*
@@ -711,6 +725,7 @@ CreateSubscription(ParseState *pstate, CreateSubscriptionStmt *stmt,
 	values[Anum_pg_subscription_subpasswordrequired - 1] = BoolGetDatum(opts.passwordrequired);
 	values[Anum_pg_subscription_subrunasowner - 1] = BoolGetDatum(opts.runasowner);
 	values[Anum_pg_subscription_subfailover - 1] = BoolGetDatum(opts.failover);
+	values[Anum_pg_subscription_subforcealter - 1] = BoolGetDatum(opts.force_alter);
 	values[Anum_pg_subscription_subconninfo - 1] =
 		CStringGetTextDatum(conninfo);
 	if (opts.slot_name)
@@ -1150,7 +1165,7 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 								  SUBOPT_DISABLE_ON_ERR |
 								  SUBOPT_PASSWORD_REQUIRED |
 								  SUBOPT_RUN_AS_OWNER | SUBOPT_FAILOVER |
-								  SUBOPT_ORIGIN);
+								  SUBOPT_ORIGIN | SUBOPT_FORCE_ALTER);
 
 				parse_subscription_options(pstate, stmt->options,
 										   supported_opts, &opts);
@@ -1213,6 +1228,23 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 						if (sub->twophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
 							(prepared_xacts = GetGidListBySubid(subid)) != NIL)
 						{
+							bool		raise_error =
+								IsSet(opts.specified_opts, SUBOPT_FORCE_ALTER) ?
+								!opts.force_alter : !sub->forcealter;
+
+							/*
+							 * Abort prepared transactions only if
+							 * 'force_alter' option is true. Otherwise raise
+							 * an ERROR.
+							 */
+							if (raise_error)
+								ereport(ERROR,
+										(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+										 errmsg("cannot alter %s when there are prepared transactions",
+												"two_phase = false"),
+										 errhint("Resolve these transactions or set %s, and then try again.",
+												 "force_alter = true")));
+
 							/* Abort all listed transactions */
 							foreach_ptr(char, gid, prepared_xacts)
 								FinishPreparedTransaction(gid, false);
diff --git a/src/bin/pg_dump/pg_dump.c b/src/bin/pg_dump/pg_dump.c
index e324070828..80139ea2cd 100644
--- a/src/bin/pg_dump/pg_dump.c
+++ b/src/bin/pg_dump/pg_dump.c
@@ -4739,6 +4739,7 @@ getSubscriptions(Archive *fout)
 	int			i_suboriginremotelsn;
 	int			i_subenabled;
 	int			i_subfailover;
+	int			i_subforcealter;
 	int			i,
 				ntups;
 
@@ -4811,10 +4812,17 @@ getSubscriptions(Archive *fout)
 
 	if (fout->remoteVersion >= 170000)
 		appendPQExpBufferStr(query,
-							 " s.subfailover\n");
+							 " s.subfailover,\n");
 	else
 		appendPQExpBuffer(query,
-						  " false AS subfailover\n");
+						  " false AS subfailover,\n");
+
+	if (fout->remoteVersion >= 170000)
+		appendPQExpBufferStr(query,
+							 " s.subforcealter\n");
+	else
+		appendPQExpBuffer(query,
+						  " false AS subforcealter\n");
 
 	appendPQExpBufferStr(query,
 						 "FROM pg_subscription s\n");
@@ -4854,6 +4862,7 @@ getSubscriptions(Archive *fout)
 	i_suboriginremotelsn = PQfnumber(res, "suboriginremotelsn");
 	i_subenabled = PQfnumber(res, "subenabled");
 	i_subfailover = PQfnumber(res, "subfailover");
+	i_subforcealter = PQfnumber(res, "subforcealter");
 
 	subinfo = pg_malloc(ntups * sizeof(SubscriptionInfo));
 
@@ -4900,6 +4909,8 @@ getSubscriptions(Archive *fout)
 			pg_strdup(PQgetvalue(res, i, i_subenabled));
 		subinfo[i].subfailover =
 			pg_strdup(PQgetvalue(res, i, i_subfailover));
+		subinfo[i].subforcealter =
+			pg_strdup(PQgetvalue(res, i, i_subforcealter));
 
 		/* Decide whether we want to dump it */
 		selectDumpableObject(&(subinfo[i].dobj), fout);
@@ -5140,6 +5151,9 @@ dumpSubscription(Archive *fout, const SubscriptionInfo *subinfo)
 	if (strcmp(subinfo->subfailover, "t") == 0)
 		appendPQExpBufferStr(query, ", failover = true");
 
+	if (strcmp(subinfo->subforcealter, "t") == 0)
+		appendPQExpBufferStr(query, ", force_alter = true");
+
 	if (strcmp(subinfo->subsynccommit, "off") != 0)
 		appendPQExpBuffer(query, ", synchronous_commit = %s", fmtId(subinfo->subsynccommit));
 
diff --git a/src/bin/pg_dump/pg_dump.h b/src/bin/pg_dump/pg_dump.h
index 865823868f..bb0fda3b29 100644
--- a/src/bin/pg_dump/pg_dump.h
+++ b/src/bin/pg_dump/pg_dump.h
@@ -671,6 +671,7 @@ typedef struct _SubscriptionInfo
 	char	   *suborigin;
 	char	   *suboriginremotelsn;
 	char	   *subfailover;
+	char	   *subforcealter;
 } SubscriptionInfo;
 
 /*
diff --git a/src/bin/psql/describe.c b/src/bin/psql/describe.c
index f67bf0b892..dba229a25d 100644
--- a/src/bin/psql/describe.c
+++ b/src/bin/psql/describe.c
@@ -6529,7 +6529,7 @@ describeSubscriptions(const char *pattern, bool verbose)
 	printQueryOpt myopt = pset.popt;
 	static const bool translate_columns[] = {false, false, false, false,
 		false, false, false, false, false, false, false, false, false, false,
-	false};
+	false, false};
 
 	if (pset.sversion < 100000)
 	{
@@ -6598,6 +6598,11 @@ describeSubscriptions(const char *pattern, bool verbose)
 							  ", subfailover AS \"%s\"\n",
 							  gettext_noop("Failover"));
 
+		if (pset.sversion >= 170000)
+			appendPQExpBuffer(&buf,
+							  ", subforcealter AS \"%s\"\n",
+							  gettext_noop("Force alter"));
+
 		appendPQExpBuffer(&buf,
 						  ",  subsynccommit AS \"%s\"\n"
 						  ",  subconninfo AS \"%s\"\n",
diff --git a/src/include/catalog/pg_subscription.h b/src/include/catalog/pg_subscription.h
index 0aa14ec4a2..deac7aa943 100644
--- a/src/include/catalog/pg_subscription.h
+++ b/src/include/catalog/pg_subscription.h
@@ -98,6 +98,13 @@ CATALOG(pg_subscription,6100,SubscriptionRelationId) BKI_SHARED_RELATION BKI_ROW
 								 * slots) in the upstream database are enabled
 								 * to be synchronized to the standbys. */
 
+	bool		subforcealter;	/* True allows the ALTER SUBSCRIPTION command
+								 * to proceed under conditions that would
+								 * otherwise result in an error. Currently,
+								 * 'force_alter' only has an effect when
+								 * altering the two_phase option from "true"
+								 * to "false". */
+
 #ifdef CATALOG_VARLEN			/* variable-length fields start here */
 	/* Connection string to the publisher */
 	text		subconninfo BKI_FORCE_NOT_NULL;
@@ -151,6 +158,12 @@ typedef struct Subscription
 								 * (i.e. the main slot and the table sync
 								 * slots) in the upstream database are enabled
 								 * to be synchronized to the standbys. */
+	bool		forcealter;		/* True allows the ALTER SUBSCRIPTION command
+								 * to proceed under conditions that would
+								 * otherwise result in an error. Currently,
+								 * 'force_alter' only has an effect when
+								 * altering the two_phase option from "true"
+								 * to "false". */
 	char	   *conninfo;		/* Connection string to the publisher */
 	char	   *slotname;		/* Name of the replication slot */
 	char	   *synccommit;		/* Synchronous commit setting for worker */
diff --git a/src/test/regress/expected/subscription.out b/src/test/regress/expected/subscription.out
index 51fa4b9690..b36fc6b8f7 100644
--- a/src/test/regress/expected/subscription.out
+++ b/src/test/regress/expected/subscription.out
@@ -116,18 +116,18 @@ CREATE SUBSCRIPTION regress_testsub4 CONNECTION 'dbname=regress_doesnotexist' PU
 WARNING:  subscription was created, but is not connected
 HINT:  To initiate replication, you must manually create the replication slot, enable the subscription, and refresh the subscription.
 \dRs+ regress_testsub4
-                                                                                                                 List of subscriptions
-       Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
-------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub4 | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | none   | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                        List of subscriptions
+       Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub4 | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | none   | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub4 SET (origin = any);
 \dRs+ regress_testsub4
-                                                                                                                 List of subscriptions
-       Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
-------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub4 | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                        List of subscriptions
+       Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub4 | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 DROP SUBSCRIPTION regress_testsub3;
@@ -145,10 +145,10 @@ ALTER SUBSCRIPTION regress_testsub CONNECTION 'foobar';
 ERROR:  invalid connection string syntax: missing "=" after "foobar" in connection info string
 
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET PUBLICATION testpub2, testpub3 WITH (refresh = false);
@@ -157,10 +157,10 @@ ALTER SUBSCRIPTION regress_testsub SET (slot_name = 'newname');
 ALTER SUBSCRIPTION regress_testsub SET (password_required = false);
 ALTER SUBSCRIPTION regress_testsub SET (run_as_owner = true);
 \dRs+
-                                                                                                                     List of subscriptions
-      Name       |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |           Conninfo           | Skip LSN 
------------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+------------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | f                 | t             | f        | off                | dbname=regress_doesnotexist2 | 0/0
+                                                                                                                            List of subscriptions
+      Name       |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |           Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+------------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | f                 | t             | f        | f           | off                | dbname=regress_doesnotexist2 | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (password_required = true);
@@ -176,10 +176,10 @@ ERROR:  unrecognized subscription parameter: "create_slot"
 -- ok
 ALTER SUBSCRIPTION regress_testsub SKIP (lsn = '0/12345');
 \dRs+
-                                                                                                                     List of subscriptions
-      Name       |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |           Conninfo           | Skip LSN 
------------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+------------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist2 | 0/12345
+                                                                                                                            List of subscriptions
+      Name       |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |           Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+------------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist2 | 0/12345
 (1 row)
 
 -- ok - with lsn = NONE
@@ -188,10 +188,10 @@ ALTER SUBSCRIPTION regress_testsub SKIP (lsn = NONE);
 ALTER SUBSCRIPTION regress_testsub SKIP (lsn = '0/0');
 ERROR:  invalid WAL location (LSN): 0/0
 \dRs+
-                                                                                                                     List of subscriptions
-      Name       |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |           Conninfo           | Skip LSN 
------------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+------------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist2 | 0/0
+                                                                                                                            List of subscriptions
+      Name       |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |           Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+------------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist2 | 0/0
 (1 row)
 
 BEGIN;
@@ -223,10 +223,10 @@ ALTER SUBSCRIPTION regress_testsub_foo SET (synchronous_commit = foobar);
 ERROR:  invalid value for parameter "synchronous_commit": "foobar"
 HINT:  Available values: local, remote_write, remote_apply, on, off.
 \dRs+
-                                                                                                                       List of subscriptions
-        Name         |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |           Conninfo           | Skip LSN 
----------------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+------------------------------+----------
- regress_testsub_foo | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | t                 | f             | f        | local              | dbname=regress_doesnotexist2 | 0/0
+                                                                                                                              List of subscriptions
+        Name         |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |           Conninfo           | Skip LSN 
+---------------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+------------------------------+----------
+ regress_testsub_foo | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | t                 | f             | f        | f           | local              | dbname=regress_doesnotexist2 | 0/0
 (1 row)
 
 -- rename back to keep the rest simple
@@ -255,19 +255,19 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 WARNING:  subscription was created, but is not connected
 HINT:  To initiate replication, you must manually create the replication slot, enable the subscription, and refresh the subscription.
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | t      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | t      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (binary = false);
 ALTER SUBSCRIPTION regress_testsub SET (slot_name = NONE);
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 DROP SUBSCRIPTION regress_testsub;
@@ -279,27 +279,27 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 WARNING:  subscription was created, but is not connected
 HINT:  To initiate replication, you must manually create the replication slot, enable the subscription, and refresh the subscription.
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | on        | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | on        | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (streaming = parallel);
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | parallel  | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | parallel  | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (streaming = false);
 ALTER SUBSCRIPTION regress_testsub SET (slot_name = NONE);
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 -- fail - publication already exists
@@ -314,10 +314,10 @@ ALTER SUBSCRIPTION regress_testsub ADD PUBLICATION testpub1, testpub2 WITH (refr
 ALTER SUBSCRIPTION regress_testsub ADD PUBLICATION testpub1, testpub2 WITH (refresh = false);
 ERROR:  publication "testpub1" is already in subscription "regress_testsub"
 \dRs+
-                                                                                                                        List of subscriptions
-      Name       |           Owner           | Enabled |         Publication         | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-----------------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub,testpub1,testpub2} | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                               List of subscriptions
+      Name       |           Owner           | Enabled |         Publication         | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-----------------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub,testpub1,testpub2} | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 -- fail - publication used more than once
@@ -332,10 +332,10 @@ ERROR:  publication "testpub3" is not in subscription "regress_testsub"
 -- ok - delete publications
 ALTER SUBSCRIPTION regress_testsub DROP PUBLICATION testpub1, testpub2 WITH (refresh = false);
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 DROP SUBSCRIPTION regress_testsub;
@@ -371,19 +371,19 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 WARNING:  subscription was created, but is not connected
 HINT:  To initiate replication, you must manually create the replication slot, enable the subscription, and refresh the subscription.
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | p                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | p                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 -- We can alter streaming when two_phase enabled
 ALTER SUBSCRIPTION regress_testsub SET (streaming = true);
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | on        | p                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | on        | p                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (slot_name = NONE);
@@ -393,10 +393,10 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 WARNING:  subscription was created, but is not connected
 HINT:  To initiate replication, you must manually create the replication slot, enable the subscription, and refresh the subscription.
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | on        | p                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | on        | p                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (slot_name = NONE);
@@ -409,18 +409,18 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 WARNING:  subscription was created, but is not connected
 HINT:  To initiate replication, you must manually create the replication slot, enable the subscription, and refresh the subscription.
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (disable_on_error = true);
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | t                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | t                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (slot_name = NONE);
diff --git a/src/test/subscription/t/099_twophase_added.pl b/src/test/subscription/t/099_twophase_added.pl
index 635daf7a78..4da8392962 100644
--- a/src/test/subscription/t/099_twophase_added.pl
+++ b/src/test/subscription/t/099_twophase_added.pl
@@ -117,15 +117,43 @@ $result = $node_subscriber->safe_psql('postgres',
 	"SELECT count(*) FROM pg_prepared_xacts;");
 is($result, q(1), "transaction has been prepared on subscriber");
 
-# Toggle the two_phase to "false" before the COMMIT PREPARED
-$node_subscriber->safe_psql(
-	'postgres', "
-    ALTER SUBSCRIPTION regress_sub DISABLE;
-    ALTER SUBSCRIPTION regress_sub SET (two_phase = false);
-    ALTER SUBSCRIPTION regress_sub ENABLE;");
+# Disable the subscription to alter the two_phase option
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION regress_sub DISABLE;");
+
+# Try altering the two_phase option to "false". The command will fail since
+# there is a prepared transaction and the 'force_alter' option is not specified
+# as true.
+my $stdout;
+my $stderr;
+
+($result, $stdout, $stderr) = $node_subscriber->psql('postgres',
+	"ALTER SUBSCRIPTION regress_sub SET (two_phase = false);");
+ok( $stderr =~
+	  /cannot alter two_phase = false when there are prepared transactions/,
+	'ALTER SUBSCRIPTION failed');
+
+# Verify the prepared transaction still exists
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT count(*) FROM pg_prepared_xacts;");
+is($result, q(1), "prepared transaction still exists");
+
+$log_offset = -s $node_subscriber->logfile;
+
+# Alter the two_phase true to false with the force_alter option enabled. This
+# command will succeed after aborting the prepared transaction.
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION regress_sub SET (two_phase = false, force_alter = true);"
+);
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION regress_sub ENABLE;");
+
+# Verify the started worker recognized two_phase was disabled
+$node_subscriber->wait_for_log(
+	'logical replication apply worker for subscription "regress_sub" two_phase is DISABLED',
+	$log_offset);
 
-# Verify any prepared transactions are aborted because two_phase is changed to
-# "false".
+# # Verify the prepared transaction was aborted
 $result = $node_subscriber->safe_psql('postgres',
 	"SELECT count(*) FROM pg_prepared_xacts;");
 is($result, q(0), "prepared transaction done by worker is aborted");
-- 
2.43.0

From 3eeec94aa618c92b3ffedafe2499532cff75a8ee Mon Sep 17 00:00:00 2001
From: Ajin Cherian <ajinc@fast.au.fujitsu.com>
Date: Fri, 5 Apr 2024 06:47:18 -0400
Subject: [PATCH v13 1/4] Allow altering of two_phase option of a SUBSCRIPTION

This patch allows the user to alter the 'two_phase' option of a subscriber provided no
uncommitted prepared transactions are pending on that subscription.

Author: Cherian Ajin, Hayato Kuroda
---
 doc/src/sgml/ref/alter_subscription.sgml      | 12 ++--
 src/backend/access/transam/twophase.c         | 62 ++++++++++++++++
 src/backend/commands/subscriptioncmds.c       | 68 ++++++++++++++----
 .../libpqwalreceiver/libpqwalreceiver.c       |  9 +--
 src/backend/replication/logical/launcher.c    | 22 ++++++
 src/backend/replication/logical/worker.c      | 21 +-----
 src/backend/replication/slot.c                | 18 ++++-
 src/backend/replication/walsender.c           | 18 ++++-
 src/bin/psql/tab-complete.c                   |  2 +-
 src/include/access/twophase.h                 |  5 ++
 src/include/replication/slot.h                |  3 +-
 src/include/replication/walreceiver.h         | 11 +--
 src/include/replication/worker_internal.h     |  1 +
 src/test/regress/expected/subscription.out    |  5 +-
 src/test/regress/sql/subscription.sql         |  5 +-
 src/test/subscription/t/021_twophase.pl       | 71 ++++++++++++++++++-
 16 files changed, 270 insertions(+), 63 deletions(-)

diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index 476f195622..0b23df1b77 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -68,8 +68,9 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
   <para>
    Commands <command>ALTER SUBSCRIPTION ... REFRESH PUBLICATION</command>,
    <command>ALTER SUBSCRIPTION ... {SET|ADD|DROP} PUBLICATION ...</command>
-   with <literal>refresh</literal> option as <literal>true</literal> and
-   <command>ALTER SUBSCRIPTION ... SET (failover = true|false)</command>
+   with <literal>refresh</literal> option as <literal>true</literal>,
+   <command>ALTER SUBSCRIPTION ... SET (failover = true|false)</command> and
+   <command>ALTER SUBSCRIPTION ... SET (two_phase = true|false)</command>
    cannot be executed inside a transaction block.
 
    These commands also cannot be executed when the subscription has
@@ -228,9 +229,12 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-disable-on-error"><literal>disable_on_error</literal></link>,
       <link linkend="sql-createsubscription-params-with-password-required"><literal>password_required</literal></link>,
       <link linkend="sql-createsubscription-params-with-run-as-owner"><literal>run_as_owner</literal></link>,
-      <link linkend="sql-createsubscription-params-with-origin"><literal>origin</literal></link>, and
-      <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>.
+      <link linkend="sql-createsubscription-params-with-origin"><literal>origin</literal></link>,
+      <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>, and
+      <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>.
       Only a superuser can set <literal>password_required = false</literal>.
+      The <literal>two_phase</literal> parameter can only be altered when the
+      subscription is disabled.
      </para>
 
      <para>
diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index bf451d42ff..0d51c31eb6 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -2682,3 +2682,65 @@ LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 	LWLockRelease(TwoPhaseStateLock);
 	return found;
 }
+
+/*
+ * TwoPhaseTransactionGid
+ *		Form the prepared transaction GID for two_phase transactions.
+ *
+ * Return the GID in the supplied buffer.
+ */
+void
+TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid, int szgid)
+{
+	Assert(subid != InvalidRepOriginId);
+
+	if (!TransactionIdIsValid(xid))
+		ereport(ERROR,
+				(errcode(ERRCODE_PROTOCOL_VIOLATION),
+				 errmsg_internal("invalid two-phase transaction ID")));
+
+	snprintf(gid, szgid, "pg_gid_%u_%u", subid, xid);
+}
+
+/*
+ * IsTwoPhaseTransactionGidForSubid
+ *		Check whether the given GID (as formed by TwoPhaseTransactionGid) is
+ *		for the specified 'subid'.
+ */
+static bool
+IsTwoPhaseTransactionGidForSubid(Oid subid, char *gid)
+{
+	int			ret;
+	Oid			subid_written;
+	TransactionId xid;
+
+	ret = sscanf(gid, "pg_gid_%u_%u", &subid_written, &xid);
+
+	return (ret == 2 && subid == subid_written);
+}
+
+/*
+ * LookupGXactBySubid
+ *		Check if the prepared transaction done by apply worker exists.
+ */
+bool
+LookupGXactBySubid(Oid subid)
+{
+	bool		found = false;
+
+	LWLockAcquire(TwoPhaseStateLock, LW_SHARED);
+	for (int i = 0; i < TwoPhaseState->numPrepXacts; i++)
+	{
+		GlobalTransaction gxact = TwoPhaseState->prepXacts[i];
+
+		/* Ignore not-yet-valid GIDs. */
+		if (gxact->valid &&
+			IsTwoPhaseTransactionGidForSubid(subid, gxact->gid))
+		{
+			found = true;
+			break;
+		}
+	}
+	LWLockRelease(TwoPhaseStateLock);
+	return found;
+}
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index e407428dbc..e925158a4d 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -16,6 +16,7 @@
 
 #include "access/htup_details.h"
 #include "access/table.h"
+#include "access/twophase.h"
 #include "access/xact.h"
 #include "catalog/catalog.h"
 #include "catalog/dependency.h"
@@ -1143,7 +1144,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 			{
 				supported_opts = (SUBOPT_SLOT_NAME |
 								  SUBOPT_SYNCHRONOUS_COMMIT | SUBOPT_BINARY |
-								  SUBOPT_STREAMING | SUBOPT_DISABLE_ON_ERR |
+								  SUBOPT_STREAMING | SUBOPT_TWOPHASE_COMMIT |
+								  SUBOPT_DISABLE_ON_ERR |
 								  SUBOPT_PASSWORD_REQUIRED |
 								  SUBOPT_RUN_AS_OWNER | SUBOPT_FAILOVER |
 								  SUBOPT_ORIGIN);
@@ -1151,6 +1153,53 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 				parse_subscription_options(pstate, stmt->options,
 										   supported_opts, &opts);
 
+				if (IsSet(opts.specified_opts, SUBOPT_TWOPHASE_COMMIT))
+				{
+					/*
+					 * Do not allow changing the two_phase option if the
+					 * subscription is enabled. This is because the two_phase
+					 * option of the slot on the publisher cannot be modified
+					 * if the slot is currently acquired by the apply worker.
+					 */
+					if (form->subenabled)
+						ereport(ERROR,
+								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+								 errmsg("cannot set %s for enabled subscription",
+										"two_phase")));
+
+					/*
+					 * Stop all the subscription workers, just in case.
+					 * Workers may still survive even if the subscription is
+					 * disabled.
+					 */
+					logicalrep_workers_stop(subid);
+
+					/*
+					 * two_phase cannot be disabled if there are any
+					 * uncommitted prepared transactions present.
+					 */
+					if (!opts.twophase &&
+						form->subtwophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
+						LookupGXactBySubid(subid))
+						ereport(ERROR,
+								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+								 errmsg("cannot disable two_phase when uncommitted prepared transactions present"),
+								 errhint("Resolve these transactions and try again")));
+
+					/*
+					 * The changed two_phase option of the slot can't be
+					 * rolled back.
+					 */
+					PreventInTransactionBlock(isTopLevel, "ALTER SUBSCRIPTION ... SET (two_phase)");
+
+					/* Change system catalog acoordingly */
+					values[Anum_pg_subscription_subtwophasestate - 1] =
+						CharGetDatum(opts.twophase ?
+									 LOGICALREP_TWOPHASE_STATE_PENDING :
+									 LOGICALREP_TWOPHASE_STATE_DISABLED);
+					replaces[Anum_pg_subscription_subtwophasestate - 1] = true;
+				}
+
 				if (IsSet(opts.specified_opts, SUBOPT_SLOT_NAME))
 				{
 					/*
@@ -1505,7 +1554,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 	 * doing the database operations we won't be able to rollback altered
 	 * slot.
 	 */
-	if (replaces[Anum_pg_subscription_subfailover - 1])
+	if (replaces[Anum_pg_subscription_subfailover - 1] ||
+		replaces[Anum_pg_subscription_subtwophasestate - 1])
 	{
 		bool		must_use_password;
 		char	   *err;
@@ -1525,7 +1575,7 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 
 		PG_TRY();
 		{
-			walrcv_alter_slot(wrconn, sub->slotname, opts.failover);
+			walrcv_alter_slot(wrconn, sub->slotname, opts.failover, opts.twophase);
 		}
 		PG_FINALLY();
 		{
@@ -1562,7 +1612,6 @@ DropSubscription(DropSubscriptionStmt *stmt, bool isTopLevel)
 	char	   *subname;
 	char	   *conninfo;
 	char	   *slotname;
-	List	   *subworkers;
 	ListCell   *lc;
 	char		originname[NAMEDATALEN];
 	char	   *err = NULL;
@@ -1672,16 +1721,7 @@ DropSubscription(DropSubscriptionStmt *stmt, bool isTopLevel)
 	 * New workers won't be started because we hold an exclusive lock on the
 	 * subscription till the end of the transaction.
 	 */
-	LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
-	subworkers = logicalrep_workers_find(subid, false);
-	LWLockRelease(LogicalRepWorkerLock);
-	foreach(lc, subworkers)
-	{
-		LogicalRepWorker *w = (LogicalRepWorker *) lfirst(lc);
-
-		logicalrep_worker_stop(w->subid, w->relid);
-	}
-	list_free(subworkers);
+	logicalrep_workers_stop(subid);
 
 	/*
 	 * Remove the no-longer-useful entry in the launcher's table of apply
diff --git a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
index 02f12f2921..2f035a0c3c 100644
--- a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
+++ b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
@@ -80,7 +80,7 @@ static char *libpqrcv_create_slot(WalReceiverConn *conn,
 								  CRSSnapshotAction snapshot_action,
 								  XLogRecPtr *lsn);
 static void libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-								bool failover);
+								bool failover, bool two_phase);
 static pid_t libpqrcv_get_backend_pid(WalReceiverConn *conn);
 static WalRcvExecResult *libpqrcv_exec(WalReceiverConn *conn,
 									   const char *query,
@@ -1121,15 +1121,16 @@ libpqrcv_create_slot(WalReceiverConn *conn, const char *slotname,
  */
 static void
 libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-					bool failover)
+					bool failover, bool two_phase)
 {
 	StringInfoData cmd;
 	PGresult   *res;
 
 	initStringInfo(&cmd);
-	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( FAILOVER %s )",
+	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( FAILOVER %s, TWO_PHASE %s )",
 					 quote_identifier(slotname),
-					 failover ? "true" : "false");
+					 failover ? "true" : "false",
+					 two_phase ? "true" : "false");
 
 	res = libpqrcv_PQexec(conn->streamConn, cmd.data);
 	pfree(cmd.data);
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 27c3a91fb7..bef65b839b 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -623,6 +623,28 @@ logicalrep_worker_stop(Oid subid, Oid relid)
 	LWLockRelease(LogicalRepWorkerLock);
 }
 
+/*
+ * Stop all the subscription workers.
+ */
+void
+logicalrep_workers_stop(Oid subid)
+{
+	List	   *subworkers;
+	ListCell   *lc;
+
+	LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
+	/* XXX clarify the reason why not only running workers are listed. */
+	subworkers = logicalrep_workers_find(subid, false);
+	LWLockRelease(LogicalRepWorkerLock);
+	foreach(lc, subworkers)
+	{
+		LogicalRepWorker *w = (LogicalRepWorker *) lfirst(lc);
+
+		logicalrep_worker_stop(w->subid, w->relid);
+	}
+	list_free(subworkers);
+}
+
 /*
  * Stop the given logical replication parallel apply worker.
  *
diff --git a/src/backend/replication/logical/worker.c b/src/backend/replication/logical/worker.c
index b5a80fe3e8..dcf656fd45 100644
--- a/src/backend/replication/logical/worker.c
+++ b/src/backend/replication/logical/worker.c
@@ -402,7 +402,6 @@ static void apply_handle_tuple_routing(ApplyExecutionData *edata,
 									   CmdType operation);
 
 /* Compute GID for two_phase transactions */
-static void TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid, int szgid);
 
 /* Functions for skipping changes */
 static void maybe_start_skipping_changes(XLogRecPtr finish_lsn);
@@ -3911,7 +3910,7 @@ maybe_reread_subscription(void)
 	/* !slotname should never happen when enabled is true. */
 	Assert(newsub->slotname);
 
-	/* two-phase should not be altered */
+	/* two-phase cannot be altered while the worker exists */
 	Assert(newsub->twophasestate == MySubscription->twophasestate);
 
 	/*
@@ -4396,24 +4395,6 @@ cleanup_subxact_info()
 	subxact_data.nsubxacts_max = 0;
 }
 
-/*
- * Form the prepared transaction GID for two_phase transactions.
- *
- * Return the GID in the supplied buffer.
- */
-static void
-TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid, int szgid)
-{
-	Assert(subid != InvalidRepOriginId);
-
-	if (!TransactionIdIsValid(xid))
-		ereport(ERROR,
-				(errcode(ERRCODE_PROTOCOL_VIOLATION),
-				 errmsg_internal("invalid two-phase transaction ID")));
-
-	snprintf(gid, szgid, "pg_gid_%u_%u", subid, xid);
-}
-
 /*
  * Common function to run the apply loop with error handling. Disable the
  * subscription, if necessary.
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 564cfee127..02e58d2a68 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -804,8 +804,10 @@ ReplicationSlotDrop(const char *name, bool nowait)
  * Change the definition of the slot identified by the specified name.
  */
 void
-ReplicationSlotAlter(const char *name, bool failover)
+ReplicationSlotAlter(const char *name, bool failover, bool two_phase)
 {
+	bool		update_slot = false;
+
 	Assert(MyReplicationSlot == NULL);
 
 	ReplicationSlotAcquire(name, false);
@@ -854,6 +856,20 @@ ReplicationSlotAlter(const char *name, bool failover)
 		MyReplicationSlot->data.failover = failover;
 		SpinLockRelease(&MyReplicationSlot->mutex);
 
+		update_slot = true;
+	}
+
+	if (MyReplicationSlot->data.two_phase != two_phase)
+	{
+		SpinLockAcquire(&MyReplicationSlot->mutex);
+		MyReplicationSlot->data.two_phase = two_phase;
+		SpinLockRelease(&MyReplicationSlot->mutex);
+
+		update_slot = true;
+	}
+
+	if (update_slot)
+	{
 		ReplicationSlotMarkDirty();
 		ReplicationSlotSave();
 	}
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index c623b07cf0..2e6ca35049 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1411,9 +1411,11 @@ DropReplicationSlot(DropReplicationSlotCmd *cmd)
  * Process extra options given to ALTER_REPLICATION_SLOT.
  */
 static void
-ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd, bool *failover)
+ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd,
+						  bool *failover, bool *two_phase)
 {
 	bool		failover_given = false;
+	bool		two_phase_given = false;
 
 	/* Parse options */
 	foreach_ptr(DefElem, defel, cmd->options)
@@ -1427,6 +1429,15 @@ ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd, bool *failover)
 			failover_given = true;
 			*failover = defGetBoolean(defel);
 		}
+		else if (strcmp(defel->defname, "two_phase") == 0)
+		{
+			if (two_phase_given)
+				ereport(ERROR,
+						(errcode(ERRCODE_SYNTAX_ERROR),
+						 errmsg("conflicting or redundant options")));
+			two_phase_given = true;
+			*two_phase = defGetBoolean(defel);
+		}
 		else
 			elog(ERROR, "unrecognized option: %s", defel->defname);
 	}
@@ -1439,9 +1450,10 @@ static void
 AlterReplicationSlot(AlterReplicationSlotCmd *cmd)
 {
 	bool		failover = false;
+	bool		two_phase = false;
 
-	ParseAlterReplSlotOptions(cmd, &failover);
-	ReplicationSlotAlter(cmd->slotname, failover);
+	ParseAlterReplSlotOptions(cmd, &failover, &two_phase);
+	ReplicationSlotAlter(cmd->slotname, failover, two_phase);
 }
 
 /*
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
index d453e224d9..891face1b6 100644
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -1948,7 +1948,7 @@ psql_completion(const char *text, int start, int end)
 	else if (HeadMatches("ALTER", "SUBSCRIPTION", MatchAny) && TailMatches("SET", "("))
 		COMPLETE_WITH("binary", "disable_on_error", "failover", "origin",
 					  "password_required", "run_as_owner", "slot_name",
-					  "streaming", "synchronous_commit");
+					  "streaming", "synchronous_commit", "two_phase");
 	/* ALTER SUBSCRIPTION <name> SKIP ( */
 	else if (HeadMatches("ALTER", "SUBSCRIPTION", MatchAny) && TailMatches("SKIP", "("))
 		COMPLETE_WITH("lsn");
diff --git a/src/include/access/twophase.h b/src/include/access/twophase.h
index 56248c0006..d37e06fdee 100644
--- a/src/include/access/twophase.h
+++ b/src/include/access/twophase.h
@@ -62,4 +62,9 @@ extern void PrepareRedoRemove(TransactionId xid, bool giveWarning);
 extern void restoreTwoPhaseData(void);
 extern bool LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 						TimestampTz origin_prepare_timestamp);
+
+extern void TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid,
+								   int szgid);
+extern bool LookupGXactBySubid(Oid subid);
+
 #endif							/* TWOPHASE_H */
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 1bc80960ef..014e216cf5 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -243,7 +243,8 @@ extern void ReplicationSlotCreate(const char *name, bool db_specific,
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
 extern void ReplicationSlotDropAcquired(void);
-extern void ReplicationSlotAlter(const char *name, bool failover);
+extern void ReplicationSlotAlter(const char *name, bool failover,
+								 bool two_phase);
 
 extern void ReplicationSlotAcquire(const char *name, bool nowait);
 extern void ReplicationSlotRelease(void);
diff --git a/src/include/replication/walreceiver.h b/src/include/replication/walreceiver.h
index 12f71fa99b..31fa1257ec 100644
--- a/src/include/replication/walreceiver.h
+++ b/src/include/replication/walreceiver.h
@@ -372,12 +372,13 @@ typedef char *(*walrcv_create_slot_fn) (WalReceiverConn *conn,
 /*
  * walrcv_alter_slot_fn
  *
- * Change the definition of a replication slot. Currently, it only supports
- * changing the failover property of the slot.
+ * Change the definition of a replication slot. Currently, it supports
+ * changing the failover and the two_phase property of the slot.
  */
 typedef void (*walrcv_alter_slot_fn) (WalReceiverConn *conn,
 									  const char *slotname,
-									  bool failover);
+									  bool failover,
+									  bool two_phase);
 
 /*
  * walrcv_get_backend_pid_fn
@@ -455,8 +456,8 @@ extern PGDLLIMPORT WalReceiverFunctionsType *WalReceiverFunctions;
 	WalReceiverFunctions->walrcv_send(conn, buffer, nbytes)
 #define walrcv_create_slot(conn, slotname, temporary, two_phase, failover, snapshot_action, lsn) \
 	WalReceiverFunctions->walrcv_create_slot(conn, slotname, temporary, two_phase, failover, snapshot_action, lsn)
-#define walrcv_alter_slot(conn, slotname, failover) \
-	WalReceiverFunctions->walrcv_alter_slot(conn, slotname, failover)
+#define walrcv_alter_slot(conn, slotname, failover, two_phase) \
+	WalReceiverFunctions->walrcv_alter_slot(conn, slotname, failover, two_phase)
 #define walrcv_get_backend_pid(conn) \
 	WalReceiverFunctions->walrcv_get_backend_pid(conn)
 #define walrcv_exec(conn, exec, nRetTypes, retTypes) \
diff --git a/src/include/replication/worker_internal.h b/src/include/replication/worker_internal.h
index 515aefd519..d5428263c1 100644
--- a/src/include/replication/worker_internal.h
+++ b/src/include/replication/worker_internal.h
@@ -246,6 +246,7 @@ extern bool logicalrep_worker_launch(LogicalRepWorkerType wtype,
 									 Oid userid, Oid relid,
 									 dsm_handle subworker_dsm);
 extern void logicalrep_worker_stop(Oid subid, Oid relid);
+extern void logicalrep_workers_stop(Oid subid);
 extern void logicalrep_pa_worker_stop(ParallelApplyWorkerInfo *winfo);
 extern void logicalrep_worker_wakeup(Oid subid, Oid relid);
 extern void logicalrep_worker_wakeup_ptr(LogicalRepWorker *worker);
diff --git a/src/test/regress/expected/subscription.out b/src/test/regress/expected/subscription.out
index 0f2a25cdc1..51fa4b9690 100644
--- a/src/test/regress/expected/subscription.out
+++ b/src/test/regress/expected/subscription.out
@@ -377,10 +377,7 @@ HINT:  To initiate replication, you must manually create the replication slot, e
  regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | p                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
---fail - alter of two_phase option not supported.
-ALTER SUBSCRIPTION regress_testsub SET (two_phase = false);
-ERROR:  unrecognized subscription parameter: "two_phase"
--- but can alter streaming when two_phase enabled
+-- We can alter streaming when two_phase enabled
 ALTER SUBSCRIPTION regress_testsub SET (streaming = true);
 \dRs+
                                                                                                                 List of subscriptions
diff --git a/src/test/regress/sql/subscription.sql b/src/test/regress/sql/subscription.sql
index 3e5ba4cb8c..a3886d79ca 100644
--- a/src/test/regress/sql/subscription.sql
+++ b/src/test/regress/sql/subscription.sql
@@ -256,10 +256,7 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUBLICATION testpub WITH (connect = false, two_phase = true);
 
 \dRs+
---fail - alter of two_phase option not supported.
-ALTER SUBSCRIPTION regress_testsub SET (two_phase = false);
-
--- but can alter streaming when two_phase enabled
+-- We can alter streaming when two_phase enabled
 ALTER SUBSCRIPTION regress_testsub SET (streaming = true);
 
 \dRs+
diff --git a/src/test/subscription/t/021_twophase.pl b/src/test/subscription/t/021_twophase.pl
index 9437cd4c3b..0436cafdb8 100644
--- a/src/test/subscription/t/021_twophase.pl
+++ b/src/test/subscription/t/021_twophase.pl
@@ -367,6 +367,75 @@ $result =
   $node_subscriber->safe_psql('postgres', "SELECT count(*) FROM tab_copy;");
 is($result, qq(2), 'replicated data in subscriber table');
 
+# Clean up
+$node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub");
+
+###############################
+# Disable the subscription and alter it to two_phase = false,
+# then verify that the altered subscription reflects the two_phase option.
+###############################
+
+# Alter subscription two_phase to false
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy DISABLE");
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = false)");
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy ENABLE");
+
+# Wait for subscription startup
+$node_subscriber->wait_for_subscription_sync($node_publisher, $appname_copy);
+
+# Make sure that the two-phase is disabled on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT subtwophasestate FROM pg_subscription WHERE subname = 'tap_sub_copy';"
+);
+is($result, qq(d), 'two-phase should be disabled');
+
+# Now do a prepare on the publisher and make sure that it is not replicated.
+$node_publisher->safe_psql(
+	'postgres', qq{
+    BEGIN;
+    INSERT INTO tab_copy VALUES (100);
+    PREPARE TRANSACTION 'newgid';
+	});
+
+# Wait for the subscriber to catchup
+$node_publisher->wait_for_catchup($appname_copy);
+
+# Make sure there are no prepared transactions on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT count(*) FROM pg_prepared_xacts;");
+is($result, qq(0), 'should be no prepared transactions on subscriber');
+
+# Now commit the insert and verify that it IS replicated
+$node_publisher->safe_psql('postgres', "COMMIT PREPARED 'newgid';");
+
+# Wait for the subscriber to catchup
+$node_publisher->wait_for_catchup($appname_copy);
+
+# Make sure that the committed transaction is replicated.
+$result =
+  $node_subscriber->safe_psql('postgres', "SELECT count(*) FROM tab_copy;");
+is($result, qq(3), 'replicated data in subscriber table');
+
+# Alter subscription two_phase to true
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy DISABLE");
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = true)");
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy ENABLE");
+
+# Wait for subscription startup
+$node_subscriber->wait_for_subscription_sync($node_publisher, $appname_copy);
+
+# Make sure that the two-phase is enabled on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT subtwophasestate FROM pg_subscription WHERE subname = 'tap_sub_copy';"
+);
+is($result, qq(e), 'two-phase should be enabled');
+
 $node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub_copy;");
 $node_publisher->safe_psql('postgres', "DROP PUBLICATION tap_pub_copy;");
 
@@ -374,8 +443,6 @@ $node_publisher->safe_psql('postgres', "DROP PUBLICATION tap_pub_copy;");
 # check all the cleanup
 ###############################
 
-$node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub");
-
 $result = $node_subscriber->safe_psql('postgres',
 	"SELECT count(*) FROM pg_subscription");
 is($result, qq(0), 'check subscription was dropped on subscriber');
-- 
2.43.0

From e66634d369106b908fec321a15f6514c22ef847e Mon Sep 17 00:00:00 2001
From: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Date: Wed, 17 Apr 2024 06:18:23 +0000
Subject: [PATCH v13 2/4] Alter slot option two_phase only when altering "true"
 to "false"
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Since the two_phase option is controlled by both the publisher (as a slot option)
and the subscriber (as a subscription option), the slot option must also be
modified.

Regarding the false->true case, the backend process alters the subtwophase to
LOGICALREP_TWOPHASE_STATE_PENDING once. After the subscription is enabled, a new
logical replication worker requests to change the two_phase option of its slot
from pending to true after the initial data synchronization is done. The code
path is the same as the case in which two_phase is initially set to true, so
there is no need to do something remarkable. However, for the true->false case,
the backend must connect to the publisher and expressly change the parameter
because the apply worker does not alter the option to false. Because this
operation cannot be rolled back, altering the two_phase parameter from "true"
to "false" within a transaction is prohibited.
---
 doc/src/sgml/ref/alter_subscription.sgml      |  2 +-
 src/backend/commands/subscriptioncmds.c       | 43 ++++++--
 .../libpqwalreceiver/libpqwalreceiver.c       | 23 +++--
 src/include/replication/walreceiver.h         |  5 +-
 src/test/subscription/meson.build             |  1 +
 src/test/subscription/t/099_twophase_added.pl | 99 +++++++++++++++++++
 6 files changed, 157 insertions(+), 16 deletions(-)
 create mode 100644 src/test/subscription/t/099_twophase_added.pl

diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index 0b23df1b77..475a42a2e3 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -70,7 +70,7 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
    <command>ALTER SUBSCRIPTION ... {SET|ADD|DROP} PUBLICATION ...</command>
    with <literal>refresh</literal> option as <literal>true</literal>,
    <command>ALTER SUBSCRIPTION ... SET (failover = true|false)</command> and
-   <command>ALTER SUBSCRIPTION ... SET (two_phase = true|false)</command>
+   <command>ALTER SUBSCRIPTION ... SET (two_phase = off)</command>
    cannot be executed inside a transaction block.
 
    These commands also cannot be executed when the subscription has
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index e925158a4d..996ea6b6de 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -1097,6 +1097,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 	Form_pg_subscription form;
 	bits32		supported_opts;
 	SubOpts		opts = {0};
+	bool		update_failover;
+	bool		update_two_phase;
 
 	rel = table_open(SubscriptionRelationId, RowExclusiveLock);
 
@@ -1187,10 +1189,25 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 								 errhint("Resolve these transactions and try again")));
 
 					/*
-					 * The changed two_phase option of the slot can't be
-					 * rolled back.
+					 * Altering the parameter from "true" to "false" within a
+					 * transaction is prohibited. Since the apply worker does
+					 * not alter the slot option to false, the backend must
+					 * connect to the publisher and expressly change the
+					 * parameter.
+					 *
+					 * There is no need to do something remarkable regarding
+					 * the "false" to "true" case; the backend process alters
+					 * subtwophase to LOGICALREP_TWOPHASE_STATE_PENDING once.
+					 * After the subscription is enabled, a new logical
+					 * replication worker requests to change the two_phase
+					 * option of its slot from pending to true when the
+					 * initial data synchronization is done. The code path is
+					 * the same as the case in which two_phase is initially
+					 * set to true.
 					 */
-					PreventInTransactionBlock(isTopLevel, "ALTER SUBSCRIPTION ... SET (two_phase)");
+					if (!opts.twophase)
+						PreventInTransactionBlock(isTopLevel,
+												  "ALTER SUBSCRIPTION ... SET (two_phase = false)");
 
 					/* Change system catalog acoordingly */
 					values[Anum_pg_subscription_subtwophasestate - 1] =
@@ -1548,14 +1565,24 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 	}
 
 	/*
-	 * Try to acquire the connection necessary for altering slot.
+	 * Check the need to alter the replication slot. Failover and two_phase
+	 * options are controlled by both the publisher (as a slot option) and the
+	 * subscriber (as a subscription option). The slot option must be altered
+	 * only when changing "true" to "false". The reason has already been
+	 * described in the ALTER_SUBSCRIPTION_OPTIONS section of this function.
+	 */
+	update_failover = replaces[Anum_pg_subscription_subfailover - 1];
+	update_two_phase = (replaces[Anum_pg_subscription_subtwophasestate - 1] &&
+						!opts.twophase);
+
+	/*
+	 * Try to acquire the connection necessary for altering slot, if needed.
 	 *
 	 * This has to be at the end because otherwise if there is an error while
 	 * doing the database operations we won't be able to rollback altered
 	 * slot.
 	 */
-	if (replaces[Anum_pg_subscription_subfailover - 1] ||
-		replaces[Anum_pg_subscription_subtwophasestate - 1])
+	if (update_failover || update_two_phase)
 	{
 		bool		must_use_password;
 		char	   *err;
@@ -1575,7 +1602,9 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 
 		PG_TRY();
 		{
-			walrcv_alter_slot(wrconn, sub->slotname, opts.failover, opts.twophase);
+			walrcv_alter_slot(wrconn, sub->slotname,
+							  update_failover ? &opts.failover : NULL,
+							  update_two_phase ? &opts.twophase : NULL);
 		}
 		PG_FINALLY();
 		{
diff --git a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
index 2f035a0c3c..07dfec947d 100644
--- a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
+++ b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
@@ -80,7 +80,7 @@ static char *libpqrcv_create_slot(WalReceiverConn *conn,
 								  CRSSnapshotAction snapshot_action,
 								  XLogRecPtr *lsn);
 static void libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-								bool failover, bool two_phase);
+								const bool *failover, const bool *two_phase);
 static pid_t libpqrcv_get_backend_pid(WalReceiverConn *conn);
 static WalRcvExecResult *libpqrcv_exec(WalReceiverConn *conn,
 									   const char *query,
@@ -1121,16 +1121,27 @@ libpqrcv_create_slot(WalReceiverConn *conn, const char *slotname,
  */
 static void
 libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-					bool failover, bool two_phase)
+					const bool *failover, const bool *two_phase)
 {
 	StringInfoData cmd;
 	PGresult   *res;
 
 	initStringInfo(&cmd);
-	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( FAILOVER %s, TWO_PHASE %s )",
-					 quote_identifier(slotname),
-					 failover ? "true" : "false",
-					 two_phase ? "true" : "false");
+	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( ",
+					 quote_identifier(slotname));
+
+	if (failover)
+		appendStringInfo(&cmd, "FAILOVER %s",
+						 *failover ? "true" : "false");
+
+	if (failover && two_phase)
+		appendStringInfo(&cmd, ", ");
+
+	if (two_phase)
+		appendStringInfo(&cmd, "TWO_PHASE %s",
+						 *two_phase ? "true" : "false");
+
+	appendStringInfoString(&cmd, " );");
 
 	res = libpqrcv_PQexec(conn->streamConn, cmd.data);
 	pfree(cmd.data);
diff --git a/src/include/replication/walreceiver.h b/src/include/replication/walreceiver.h
index 31fa1257ec..7ffa5a58b3 100644
--- a/src/include/replication/walreceiver.h
+++ b/src/include/replication/walreceiver.h
@@ -377,8 +377,9 @@ typedef char *(*walrcv_create_slot_fn) (WalReceiverConn *conn,
  */
 typedef void (*walrcv_alter_slot_fn) (WalReceiverConn *conn,
 									  const char *slotname,
-									  bool failover,
-									  bool two_phase);
+									  const bool *failover,
+									  const bool *two_phase);
+
 
 /*
  * walrcv_get_backend_pid_fn
diff --git a/src/test/subscription/meson.build b/src/test/subscription/meson.build
index c591cd7d61..b4bd522c3d 100644
--- a/src/test/subscription/meson.build
+++ b/src/test/subscription/meson.build
@@ -40,6 +40,7 @@ tests += {
       't/031_column_list.pl',
       't/032_subscribe_use_index.pl',
       't/033_run_as_table_owner.pl',
+      't/099_twophase_added.pl',
       't/100_bugs.pl',
     ],
   },
diff --git a/src/test/subscription/t/099_twophase_added.pl b/src/test/subscription/t/099_twophase_added.pl
new file mode 100644
index 0000000000..1124f7fa00
--- /dev/null
+++ b/src/test/subscription/t/099_twophase_added.pl
@@ -0,0 +1,99 @@
+# Copyright (c) 2024, PostgreSQL Global Development Group
+
+# Additional tests for altering two_phase option
+use strict;
+use warnings FATAL => 'all';
+use PostgreSQL::Test::Cluster;
+use PostgreSQL::Test::Utils;
+use Test::More;
+
+# Initialize publisher node
+my $node_publisher = PostgreSQL::Test::Cluster->new('publisher');
+$node_publisher->init(allows_streaming => 'logical');
+$node_publisher->append_conf('postgresql.conf',
+	qq(max_prepared_transactions = 10));
+$node_publisher->start;
+
+# Create subscriber node
+my $node_subscriber = PostgreSQL::Test::Cluster->new('subscriber');
+$node_subscriber->init;
+$node_subscriber->append_conf(
+	'postgresql.conf',
+	qq(max_prepared_transactions = 10
+	log_min_messages = debug1));
+$node_subscriber->start;
+
+# Define tables on both nodes
+$node_publisher->safe_psql('postgres',
+	"CREATE TABLE tab_full (a int PRIMARY KEY);");
+$node_subscriber->safe_psql('postgres',
+	"CREATE TABLE tab_full (a int PRIMARY KEY)");
+
+# Setup logical replication, with two_phase = "false"
+my $publisher_connstr = $node_publisher->connstr . ' dbname=postgres';
+$node_publisher->safe_psql('postgres',
+	"CREATE PUBLICATION pub FOR ALL TABLES");
+
+my $log_offset = -s $node_subscriber->logfile;
+
+$node_subscriber->safe_psql(
+	'postgres', "
+	CREATE SUBSCRIPTION regress_sub
+	CONNECTION '$publisher_connstr' PUBLICATION pub
+	WITH (two_phase = false, copy_data = false, failover = false)");
+
+# Verify the started worker recognized two_phase was disabled
+$node_subscriber->wait_for_log(
+	'logical replication apply worker for subscription "regress_sub" two_phase is DISABLED',
+	$log_offset);
+
+#####################
+# Check the case that prepared transactions exist on the publisher node.
+#
+# Since the two_phase is "false", then normally, this PREPARE will do nothing
+# until the COMMIT PREPARED, but in this test, we toggle the two_phase to
+# "true" again before the COMMIT PREPARED happens.
+
+# Prepare a transaction to insert some tuples into the table
+$node_publisher->safe_psql(
+	'postgres', "
+	BEGIN;
+	INSERT INTO tab_full VALUES (generate_series(1, 5));
+	PREPARE TRANSACTION 'test_prepared_tab_full';");
+
+$node_publisher->wait_for_catchup('regress_sub');
+
+# Verify the prepared transaction is not yet replicated to the subscriber
+# because two_phase is set to "false".
+my $result = $node_subscriber->safe_psql('postgres',
+	"SELECT count(*) FROM pg_prepared_xacts;");
+is($result, q(0), "transaction is not prepared on subscriber");
+
+$log_offset = -s $node_subscriber->logfile;
+
+# Toggle the two_phase to "true" *before* the COMMIT PREPARED. Since we are the
+# special path for the case where both two_phase and failover are altered, it
+# is also set to "true".
+$node_subscriber->safe_psql(
+	'postgres', "
+    ALTER SUBSCRIPTION regress_sub DISABLE;
+    ALTER SUBSCRIPTION regress_sub SET (two_phase = true, failover = true);
+    ALTER SUBSCRIPTION regress_sub ENABLE;");
+
+# Verify the started worker recognized two_phase was enabled
+$node_subscriber->wait_for_log(
+	'logical replication apply worker for subscription "regress_sub" two_phase is ENABLED',
+	$log_offset);
+
+# And do COMMIT PREPARED the prepared transaction
+$node_publisher->safe_psql('postgres',
+	"COMMIT PREPARED 'test_prepared_tab_full';");
+$node_publisher->wait_for_catchup('regress_sub');
+
+# Verify inserted tuples are replicated
+$result =
+  $node_subscriber->safe_psql('postgres', "SELECT count(*) FROM tab_full;");
+is($result, q(5),
+	"prepared transactions done before altering can be replicated");
+
+done_testing();
-- 
2.43.0

From bce3f77fb1009f866a0fe3fc616c8218ec900f13 Mon Sep 17 00:00:00 2001
From: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Date: Mon, 8 Apr 2024 12:39:12 +0000
Subject: [PATCH v13 3/4] Abort prepared transactions while altering two_phase
 to off

If we alter the two_phase parameter from "on" to "off" and there are prepared
transactions on the subscriber, they won't be resolved. To avoid this issue, we
allow the backend to abort all prepared transactions while altering the
subscription.
---
 doc/src/sgml/ref/alter_subscription.sgml      | 11 +++-
 src/backend/access/transam/twophase.c         | 17 ++---
 src/backend/commands/subscriptioncmds.c       | 66 +++++++++++--------
 src/include/access/twophase.h                 |  3 +-
 src/test/subscription/t/099_twophase_added.pl | 44 +++++++++++++
 5 files changed, 101 insertions(+), 40 deletions(-)

diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index 475a42a2e3..8801f37f0e 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -233,8 +233,6 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>, and
       <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>.
       Only a superuser can set <literal>password_required = false</literal>.
-      The <literal>two_phase</literal> parameter can only be altered when the
-      subscription is disabled.
      </para>
 
      <para>
@@ -256,6 +254,15 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>
       option is enabled.
      </para>
+
+     <para>
+      The <literal>two_phase</literal> parameter can only be altered when the
+      subscription is disabled. When altering the parameter from <literal>true</literal>
+      to <literal>false</literal>, the backend process checks for any incomplete
+      prepared transactions done by the logical replication worker (from when
+      <literal>two_phase</literal> parameter was still <literal>true</literal>)
+      and, if any are found, those are aborted.
+     </para>
     </listitem>
    </varlistentry>
 
diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index 0d51c31eb6..ae1a97177c 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -2720,13 +2720,13 @@ IsTwoPhaseTransactionGidForSubid(Oid subid, char *gid)
 }
 
 /*
- * LookupGXactBySubid
- *		Check if the prepared transaction done by apply worker exists.
+ * GetGidListBySubid
+ *      Get a list of GIDs which is PREPARE'd by the given subscription.
  */
-bool
-LookupGXactBySubid(Oid subid)
+List *
+GetGidListBySubid(Oid subid)
 {
-	bool		found = false;
+	List	   *list = NIL;
 
 	LWLockAcquire(TwoPhaseStateLock, LW_SHARED);
 	for (int i = 0; i < TwoPhaseState->numPrepXacts; i++)
@@ -2736,11 +2736,8 @@ LookupGXactBySubid(Oid subid)
 		/* Ignore not-yet-valid GIDs. */
 		if (gxact->valid &&
 			IsTwoPhaseTransactionGidForSubid(subid, gxact->gid))
-		{
-			found = true;
-			break;
-		}
+			list = lappend(list, pstrdup(gxact->gid));
 	}
 	LWLockRelease(TwoPhaseStateLock);
-	return found;
+	return list;
 }
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index 996ea6b6de..2532b40365 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -1177,38 +1177,50 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 					logicalrep_workers_stop(subid);
 
 					/*
-					 * two_phase cannot be disabled if there are any
-					 * uncommitted prepared transactions present.
-					 */
-					if (!opts.twophase &&
-						form->subtwophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
-						LookupGXactBySubid(subid))
-						ereport(ERROR,
-								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-								 errmsg("cannot disable two_phase when uncommitted prepared transactions present"),
-								 errhint("Resolve these transactions and try again")));
-
-					/*
-					 * Altering the parameter from "true" to "false" within a
-					 * transaction is prohibited. Since the apply worker does
-					 * not alter the slot option to false, the backend must
-					 * connect to the publisher and expressly change the
-					 * parameter.
-					 *
-					 * There is no need to do something remarkable regarding
-					 * the "false" to "true" case; the backend process alters
-					 * subtwophase to LOGICALREP_TWOPHASE_STATE_PENDING once.
-					 * After the subscription is enabled, a new logical
-					 * replication worker requests to change the two_phase
-					 * option of its slot from pending to true when the
-					 * initial data synchronization is done. The code path is
-					 * the same as the case in which two_phase is initially
-					 * set to true.
+					 * If two_phase was previously enabled, there is a
+					 * possibility that transactions have already been
+					 * PREPARE'd. They must be checked and rolled back.
 					 */
 					if (!opts.twophase)
+					{
+						List	   *prepared_xacts;
+
+						/*
+						 * Altering the parameter from "true" to "false"
+						 * within a transaction is prohibited. Since the apply
+						 * worker does not alter the slot option to false, the
+						 * backend must connect to the publisher and expressly
+						 * change the parameter.
+						 *
+						 * There is no need to do something remarkable
+						 * regarding the "false" to "true" case; the backend
+						 * process alters subtwophase to
+						 * LOGICALREP_TWOPHASE_STATE_PENDING once. After the
+						 * subscription is enabled, a new logical replication
+						 * worker requests to change the two_phase option of
+						 * its slot from pending to true when the initial data
+						 * synchronization is done. The code path is the same
+						 * as the case in which two_phase is initially
+						 * set to true.
+						 */
 						PreventInTransactionBlock(isTopLevel,
 												  "ALTER SUBSCRIPTION ... SET (two_phase = false)");
 
+						/*
+						 * To prevent prepared transactions from being
+						 * isolated, they must manually be aborted.
+						 */
+						if (sub->twophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
+							(prepared_xacts = GetGidListBySubid(subid)) != NIL)
+						{
+							/* Abort all listed transactions */
+							foreach_ptr(char, gid, prepared_xacts)
+								FinishPreparedTransaction(gid, false);
+
+							list_free_deep(prepared_xacts);
+						}
+					}
+
 					/* Change system catalog acoordingly */
 					values[Anum_pg_subscription_subtwophasestate - 1] =
 						CharGetDatum(opts.twophase ?
diff --git a/src/include/access/twophase.h b/src/include/access/twophase.h
index d37e06fdee..f7a5cf0c12 100644
--- a/src/include/access/twophase.h
+++ b/src/include/access/twophase.h
@@ -18,6 +18,7 @@
 #include "access/xlogdefs.h"
 #include "datatype/timestamp.h"
 #include "storage/lock.h"
+#include "nodes/pg_list.h"
 
 /*
  * GlobalTransactionData is defined in twophase.c; other places have no
@@ -65,6 +66,6 @@ extern bool LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 
 extern void TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid,
 								   int szgid);
-extern bool LookupGXactBySubid(Oid subid);
+extern List *GetGidListBySubid(Oid subid);
 
 #endif							/* TWOPHASE_H */
diff --git a/src/test/subscription/t/099_twophase_added.pl b/src/test/subscription/t/099_twophase_added.pl
index 1124f7fa00..635daf7a78 100644
--- a/src/test/subscription/t/099_twophase_added.pl
+++ b/src/test/subscription/t/099_twophase_added.pl
@@ -96,4 +96,48 @@ $result =
 is($result, q(5),
 	"prepared transactions done before altering can be replicated");
 
+#####################
+# Check the case that prepared transactions exist on the subscriber node
+#
+# If the two_phase is altering from "true" to "false" and there are prepared
+# transactions on the subscriber, they must be aborted. This test checks it.
+
+# Prepare a transaction to insert some tuples into the table
+$node_publisher->safe_psql(
+	'postgres', "
+	BEGIN;
+	INSERT INTO tab_full VALUES (generate_series(6, 10));
+	PREPARE TRANSACTION 'test_prepared_tab_full';");
+
+$node_publisher->wait_for_catchup('regress_sub');
+
+# Verify the prepared transaction has been replicated to the subscriber because
+# two_phase is set to "true".
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT count(*) FROM pg_prepared_xacts;");
+is($result, q(1), "transaction has been prepared on subscriber");
+
+# Toggle the two_phase to "false" before the COMMIT PREPARED
+$node_subscriber->safe_psql(
+	'postgres', "
+    ALTER SUBSCRIPTION regress_sub DISABLE;
+    ALTER SUBSCRIPTION regress_sub SET (two_phase = false);
+    ALTER SUBSCRIPTION regress_sub ENABLE;");
+
+# Verify any prepared transactions are aborted because two_phase is changed to
+# "false".
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT count(*) FROM pg_prepared_xacts;");
+is($result, q(0), "prepared transaction done by worker is aborted");
+
+# Do COMMIT PREPARED the prepared transaction
+$node_publisher->safe_psql('postgres',
+	"COMMIT PREPARED 'test_prepared_tab_full';");
+$node_publisher->wait_for_catchup('regress_sub');
+
+# Verify inserted tuples are replicated
+$result =
+  $node_subscriber->safe_psql('postgres', "SELECT count(10) FROM tab_full;");
+is($result, q(10), "prepared transactions on publisher can be replicated");
+
 done_testing();
-- 
2.43.0

From ac8631d7032ccd3a277bc4777f8ff40bd74951d4 Mon Sep 17 00:00:00 2001
From: Ajin Cherian <ajinc@fast.au.fujitsu.com>
Date: Fri, 5 Apr 2024 06:47:18 -0400
Subject: [PATCH v14 1/4] Allow altering of two_phase option of a SUBSCRIPTION

This patch allows the user to alter the 'two_phase' option of a subscriber provided no
uncommitted prepared transactions are pending on that subscription.

Author: Cherian Ajin, Hayato Kuroda
---
 doc/src/sgml/ref/alter_subscription.sgml      | 12 ++--
 src/backend/access/transam/twophase.c         | 62 ++++++++++++++++
 src/backend/commands/subscriptioncmds.c       | 68 ++++++++++++++----
 .../libpqwalreceiver/libpqwalreceiver.c       |  9 +--
 src/backend/replication/logical/launcher.c    | 22 ++++++
 src/backend/replication/logical/worker.c      | 21 +-----
 src/backend/replication/slot.c                | 18 ++++-
 src/backend/replication/walsender.c           | 18 ++++-
 src/bin/psql/tab-complete.c                   |  2 +-
 src/include/access/twophase.h                 |  5 ++
 src/include/replication/slot.h                |  3 +-
 src/include/replication/walreceiver.h         | 11 +--
 src/include/replication/worker_internal.h     |  1 +
 src/test/regress/expected/subscription.out    |  5 +-
 src/test/regress/sql/subscription.sql         |  5 +-
 src/test/subscription/t/021_twophase.pl       | 71 ++++++++++++++++++-
 16 files changed, 270 insertions(+), 63 deletions(-)

diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index 476f195622..0b23df1b77 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -68,8 +68,9 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
   <para>
    Commands <command>ALTER SUBSCRIPTION ... REFRESH PUBLICATION</command>,
    <command>ALTER SUBSCRIPTION ... {SET|ADD|DROP} PUBLICATION ...</command>
-   with <literal>refresh</literal> option as <literal>true</literal> and
-   <command>ALTER SUBSCRIPTION ... SET (failover = true|false)</command>
+   with <literal>refresh</literal> option as <literal>true</literal>,
+   <command>ALTER SUBSCRIPTION ... SET (failover = true|false)</command> and
+   <command>ALTER SUBSCRIPTION ... SET (two_phase = true|false)</command>
    cannot be executed inside a transaction block.
 
    These commands also cannot be executed when the subscription has
@@ -228,9 +229,12 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-disable-on-error"><literal>disable_on_error</literal></link>,
       <link linkend="sql-createsubscription-params-with-password-required"><literal>password_required</literal></link>,
       <link linkend="sql-createsubscription-params-with-run-as-owner"><literal>run_as_owner</literal></link>,
-      <link linkend="sql-createsubscription-params-with-origin"><literal>origin</literal></link>, and
-      <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>.
+      <link linkend="sql-createsubscription-params-with-origin"><literal>origin</literal></link>,
+      <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>, and
+      <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>.
       Only a superuser can set <literal>password_required = false</literal>.
+      The <literal>two_phase</literal> parameter can only be altered when the
+      subscription is disabled.
      </para>
 
      <para>
diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index 9a8257fcaf..35bce6809d 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -2681,3 +2681,65 @@ LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 	LWLockRelease(TwoPhaseStateLock);
 	return found;
 }
+
+/*
+ * TwoPhaseTransactionGid
+ *		Form the prepared transaction GID for two_phase transactions.
+ *
+ * Return the GID in the supplied buffer.
+ */
+void
+TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid, int szgid)
+{
+	Assert(subid != InvalidRepOriginId);
+
+	if (!TransactionIdIsValid(xid))
+		ereport(ERROR,
+				(errcode(ERRCODE_PROTOCOL_VIOLATION),
+				 errmsg_internal("invalid two-phase transaction ID")));
+
+	snprintf(gid, szgid, "pg_gid_%u_%u", subid, xid);
+}
+
+/*
+ * IsTwoPhaseTransactionGidForSubid
+ *		Check whether the given GID (as formed by TwoPhaseTransactionGid) is
+ *		for the specified 'subid'.
+ */
+static bool
+IsTwoPhaseTransactionGidForSubid(Oid subid, char *gid)
+{
+	int			ret;
+	Oid			subid_written;
+	TransactionId xid;
+
+	ret = sscanf(gid, "pg_gid_%u_%u", &subid_written, &xid);
+
+	return (ret == 2 && subid == subid_written);
+}
+
+/*
+ * LookupGXactBySubid
+ *		Check if the prepared transaction done by apply worker exists.
+ */
+bool
+LookupGXactBySubid(Oid subid)
+{
+	bool		found = false;
+
+	LWLockAcquire(TwoPhaseStateLock, LW_SHARED);
+	for (int i = 0; i < TwoPhaseState->numPrepXacts; i++)
+	{
+		GlobalTransaction gxact = TwoPhaseState->prepXacts[i];
+
+		/* Ignore not-yet-valid GIDs. */
+		if (gxact->valid &&
+			IsTwoPhaseTransactionGidForSubid(subid, gxact->gid))
+		{
+			found = true;
+			break;
+		}
+	}
+	LWLockRelease(TwoPhaseStateLock);
+	return found;
+}
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index e407428dbc..e925158a4d 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -16,6 +16,7 @@
 
 #include "access/htup_details.h"
 #include "access/table.h"
+#include "access/twophase.h"
 #include "access/xact.h"
 #include "catalog/catalog.h"
 #include "catalog/dependency.h"
@@ -1143,7 +1144,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 			{
 				supported_opts = (SUBOPT_SLOT_NAME |
 								  SUBOPT_SYNCHRONOUS_COMMIT | SUBOPT_BINARY |
-								  SUBOPT_STREAMING | SUBOPT_DISABLE_ON_ERR |
+								  SUBOPT_STREAMING | SUBOPT_TWOPHASE_COMMIT |
+								  SUBOPT_DISABLE_ON_ERR |
 								  SUBOPT_PASSWORD_REQUIRED |
 								  SUBOPT_RUN_AS_OWNER | SUBOPT_FAILOVER |
 								  SUBOPT_ORIGIN);
@@ -1151,6 +1153,53 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 				parse_subscription_options(pstate, stmt->options,
 										   supported_opts, &opts);
 
+				if (IsSet(opts.specified_opts, SUBOPT_TWOPHASE_COMMIT))
+				{
+					/*
+					 * Do not allow changing the two_phase option if the
+					 * subscription is enabled. This is because the two_phase
+					 * option of the slot on the publisher cannot be modified
+					 * if the slot is currently acquired by the apply worker.
+					 */
+					if (form->subenabled)
+						ereport(ERROR,
+								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+								 errmsg("cannot set %s for enabled subscription",
+										"two_phase")));
+
+					/*
+					 * Stop all the subscription workers, just in case.
+					 * Workers may still survive even if the subscription is
+					 * disabled.
+					 */
+					logicalrep_workers_stop(subid);
+
+					/*
+					 * two_phase cannot be disabled if there are any
+					 * uncommitted prepared transactions present.
+					 */
+					if (!opts.twophase &&
+						form->subtwophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
+						LookupGXactBySubid(subid))
+						ereport(ERROR,
+								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+								 errmsg("cannot disable two_phase when uncommitted prepared transactions present"),
+								 errhint("Resolve these transactions and try again")));
+
+					/*
+					 * The changed two_phase option of the slot can't be
+					 * rolled back.
+					 */
+					PreventInTransactionBlock(isTopLevel, "ALTER SUBSCRIPTION ... SET (two_phase)");
+
+					/* Change system catalog acoordingly */
+					values[Anum_pg_subscription_subtwophasestate - 1] =
+						CharGetDatum(opts.twophase ?
+									 LOGICALREP_TWOPHASE_STATE_PENDING :
+									 LOGICALREP_TWOPHASE_STATE_DISABLED);
+					replaces[Anum_pg_subscription_subtwophasestate - 1] = true;
+				}
+
 				if (IsSet(opts.specified_opts, SUBOPT_SLOT_NAME))
 				{
 					/*
@@ -1505,7 +1554,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 	 * doing the database operations we won't be able to rollback altered
 	 * slot.
 	 */
-	if (replaces[Anum_pg_subscription_subfailover - 1])
+	if (replaces[Anum_pg_subscription_subfailover - 1] ||
+		replaces[Anum_pg_subscription_subtwophasestate - 1])
 	{
 		bool		must_use_password;
 		char	   *err;
@@ -1525,7 +1575,7 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 
 		PG_TRY();
 		{
-			walrcv_alter_slot(wrconn, sub->slotname, opts.failover);
+			walrcv_alter_slot(wrconn, sub->slotname, opts.failover, opts.twophase);
 		}
 		PG_FINALLY();
 		{
@@ -1562,7 +1612,6 @@ DropSubscription(DropSubscriptionStmt *stmt, bool isTopLevel)
 	char	   *subname;
 	char	   *conninfo;
 	char	   *slotname;
-	List	   *subworkers;
 	ListCell   *lc;
 	char		originname[NAMEDATALEN];
 	char	   *err = NULL;
@@ -1672,16 +1721,7 @@ DropSubscription(DropSubscriptionStmt *stmt, bool isTopLevel)
 	 * New workers won't be started because we hold an exclusive lock on the
 	 * subscription till the end of the transaction.
 	 */
-	LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
-	subworkers = logicalrep_workers_find(subid, false);
-	LWLockRelease(LogicalRepWorkerLock);
-	foreach(lc, subworkers)
-	{
-		LogicalRepWorker *w = (LogicalRepWorker *) lfirst(lc);
-
-		logicalrep_worker_stop(w->subid, w->relid);
-	}
-	list_free(subworkers);
+	logicalrep_workers_stop(subid);
 
 	/*
 	 * Remove the no-longer-useful entry in the launcher's table of apply
diff --git a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
index 02f12f2921..2f035a0c3c 100644
--- a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
+++ b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
@@ -80,7 +80,7 @@ static char *libpqrcv_create_slot(WalReceiverConn *conn,
 								  CRSSnapshotAction snapshot_action,
 								  XLogRecPtr *lsn);
 static void libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-								bool failover);
+								bool failover, bool two_phase);
 static pid_t libpqrcv_get_backend_pid(WalReceiverConn *conn);
 static WalRcvExecResult *libpqrcv_exec(WalReceiverConn *conn,
 									   const char *query,
@@ -1121,15 +1121,16 @@ libpqrcv_create_slot(WalReceiverConn *conn, const char *slotname,
  */
 static void
 libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-					bool failover)
+					bool failover, bool two_phase)
 {
 	StringInfoData cmd;
 	PGresult   *res;
 
 	initStringInfo(&cmd);
-	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( FAILOVER %s )",
+	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( FAILOVER %s, TWO_PHASE %s )",
 					 quote_identifier(slotname),
-					 failover ? "true" : "false");
+					 failover ? "true" : "false",
+					 two_phase ? "true" : "false");
 
 	res = libpqrcv_PQexec(conn->streamConn, cmd.data);
 	pfree(cmd.data);
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 27c3a91fb7..bef65b839b 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -623,6 +623,28 @@ logicalrep_worker_stop(Oid subid, Oid relid)
 	LWLockRelease(LogicalRepWorkerLock);
 }
 
+/*
+ * Stop all the subscription workers.
+ */
+void
+logicalrep_workers_stop(Oid subid)
+{
+	List	   *subworkers;
+	ListCell   *lc;
+
+	LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
+	/* XXX clarify the reason why not only running workers are listed. */
+	subworkers = logicalrep_workers_find(subid, false);
+	LWLockRelease(LogicalRepWorkerLock);
+	foreach(lc, subworkers)
+	{
+		LogicalRepWorker *w = (LogicalRepWorker *) lfirst(lc);
+
+		logicalrep_worker_stop(w->subid, w->relid);
+	}
+	list_free(subworkers);
+}
+
 /*
  * Stop the given logical replication parallel apply worker.
  *
diff --git a/src/backend/replication/logical/worker.c b/src/backend/replication/logical/worker.c
index 3b285894db..33d9549f0a 100644
--- a/src/backend/replication/logical/worker.c
+++ b/src/backend/replication/logical/worker.c
@@ -402,7 +402,6 @@ static void apply_handle_tuple_routing(ApplyExecutionData *edata,
 									   CmdType operation);
 
 /* Compute GID for two_phase transactions */
-static void TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid, int szgid);
 
 /* Functions for skipping changes */
 static void maybe_start_skipping_changes(XLogRecPtr finish_lsn);
@@ -3911,7 +3910,7 @@ maybe_reread_subscription(void)
 	/* !slotname should never happen when enabled is true. */
 	Assert(newsub->slotname);
 
-	/* two-phase should not be altered */
+	/* two-phase cannot be altered while the worker exists */
 	Assert(newsub->twophasestate == MySubscription->twophasestate);
 
 	/*
@@ -4396,24 +4395,6 @@ cleanup_subxact_info()
 	subxact_data.nsubxacts_max = 0;
 }
 
-/*
- * Form the prepared transaction GID for two_phase transactions.
- *
- * Return the GID in the supplied buffer.
- */
-static void
-TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid, int szgid)
-{
-	Assert(subid != InvalidRepOriginId);
-
-	if (!TransactionIdIsValid(xid))
-		ereport(ERROR,
-				(errcode(ERRCODE_PROTOCOL_VIOLATION),
-				 errmsg_internal("invalid two-phase transaction ID")));
-
-	snprintf(gid, szgid, "pg_gid_%u_%u", subid, xid);
-}
-
 /*
  * Common function to run the apply loop with error handling. Disable the
  * subscription, if necessary.
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index baf9b89dc4..2ad6dca993 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -804,8 +804,10 @@ ReplicationSlotDrop(const char *name, bool nowait)
  * Change the definition of the slot identified by the specified name.
  */
 void
-ReplicationSlotAlter(const char *name, bool failover)
+ReplicationSlotAlter(const char *name, bool failover, bool two_phase)
 {
+	bool		update_slot = false;
+
 	Assert(MyReplicationSlot == NULL);
 
 	ReplicationSlotAcquire(name, false);
@@ -854,6 +856,20 @@ ReplicationSlotAlter(const char *name, bool failover)
 		MyReplicationSlot->data.failover = failover;
 		SpinLockRelease(&MyReplicationSlot->mutex);
 
+		update_slot = true;
+	}
+
+	if (MyReplicationSlot->data.two_phase != two_phase)
+	{
+		SpinLockAcquire(&MyReplicationSlot->mutex);
+		MyReplicationSlot->data.two_phase = two_phase;
+		SpinLockRelease(&MyReplicationSlot->mutex);
+
+		update_slot = true;
+	}
+
+	if (update_slot)
+	{
 		ReplicationSlotMarkDirty();
 		ReplicationSlotSave();
 	}
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 754f505c13..af776fccb8 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1409,9 +1409,11 @@ DropReplicationSlot(DropReplicationSlotCmd *cmd)
  * Process extra options given to ALTER_REPLICATION_SLOT.
  */
 static void
-ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd, bool *failover)
+ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd,
+						  bool *failover, bool *two_phase)
 {
 	bool		failover_given = false;
+	bool		two_phase_given = false;
 
 	/* Parse options */
 	foreach_ptr(DefElem, defel, cmd->options)
@@ -1425,6 +1427,15 @@ ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd, bool *failover)
 			failover_given = true;
 			*failover = defGetBoolean(defel);
 		}
+		else if (strcmp(defel->defname, "two_phase") == 0)
+		{
+			if (two_phase_given)
+				ereport(ERROR,
+						(errcode(ERRCODE_SYNTAX_ERROR),
+						 errmsg("conflicting or redundant options")));
+			two_phase_given = true;
+			*two_phase = defGetBoolean(defel);
+		}
 		else
 			elog(ERROR, "unrecognized option: %s", defel->defname);
 	}
@@ -1437,9 +1448,10 @@ static void
 AlterReplicationSlot(AlterReplicationSlotCmd *cmd)
 {
 	bool		failover = false;
+	bool		two_phase = false;
 
-	ParseAlterReplSlotOptions(cmd, &failover);
-	ReplicationSlotAlter(cmd->slotname, failover);
+	ParseAlterReplSlotOptions(cmd, &failover, &two_phase);
+	ReplicationSlotAlter(cmd->slotname, failover, two_phase);
 }
 
 /*
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
index d453e224d9..891face1b6 100644
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -1948,7 +1948,7 @@ psql_completion(const char *text, int start, int end)
 	else if (HeadMatches("ALTER", "SUBSCRIPTION", MatchAny) && TailMatches("SET", "("))
 		COMPLETE_WITH("binary", "disable_on_error", "failover", "origin",
 					  "password_required", "run_as_owner", "slot_name",
-					  "streaming", "synchronous_commit");
+					  "streaming", "synchronous_commit", "two_phase");
 	/* ALTER SUBSCRIPTION <name> SKIP ( */
 	else if (HeadMatches("ALTER", "SUBSCRIPTION", MatchAny) && TailMatches("SKIP", "("))
 		COMPLETE_WITH("lsn");
diff --git a/src/include/access/twophase.h b/src/include/access/twophase.h
index 56248c0006..d37e06fdee 100644
--- a/src/include/access/twophase.h
+++ b/src/include/access/twophase.h
@@ -62,4 +62,9 @@ extern void PrepareRedoRemove(TransactionId xid, bool giveWarning);
 extern void restoreTwoPhaseData(void);
 extern bool LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 						TimestampTz origin_prepare_timestamp);
+
+extern void TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid,
+								   int szgid);
+extern bool LookupGXactBySubid(Oid subid);
+
 #endif							/* TWOPHASE_H */
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index c9675ee87c..163a4a911a 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -243,7 +243,8 @@ extern void ReplicationSlotCreate(const char *name, bool db_specific,
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
 extern void ReplicationSlotDropAcquired(void);
-extern void ReplicationSlotAlter(const char *name, bool failover);
+extern void ReplicationSlotAlter(const char *name, bool failover,
+								 bool two_phase);
 
 extern void ReplicationSlotAcquire(const char *name, bool nowait);
 extern void ReplicationSlotRelease(void);
diff --git a/src/include/replication/walreceiver.h b/src/include/replication/walreceiver.h
index 12f71fa99b..31fa1257ec 100644
--- a/src/include/replication/walreceiver.h
+++ b/src/include/replication/walreceiver.h
@@ -372,12 +372,13 @@ typedef char *(*walrcv_create_slot_fn) (WalReceiverConn *conn,
 /*
  * walrcv_alter_slot_fn
  *
- * Change the definition of a replication slot. Currently, it only supports
- * changing the failover property of the slot.
+ * Change the definition of a replication slot. Currently, it supports
+ * changing the failover and the two_phase property of the slot.
  */
 typedef void (*walrcv_alter_slot_fn) (WalReceiverConn *conn,
 									  const char *slotname,
-									  bool failover);
+									  bool failover,
+									  bool two_phase);
 
 /*
  * walrcv_get_backend_pid_fn
@@ -455,8 +456,8 @@ extern PGDLLIMPORT WalReceiverFunctionsType *WalReceiverFunctions;
 	WalReceiverFunctions->walrcv_send(conn, buffer, nbytes)
 #define walrcv_create_slot(conn, slotname, temporary, two_phase, failover, snapshot_action, lsn) \
 	WalReceiverFunctions->walrcv_create_slot(conn, slotname, temporary, two_phase, failover, snapshot_action, lsn)
-#define walrcv_alter_slot(conn, slotname, failover) \
-	WalReceiverFunctions->walrcv_alter_slot(conn, slotname, failover)
+#define walrcv_alter_slot(conn, slotname, failover, two_phase) \
+	WalReceiverFunctions->walrcv_alter_slot(conn, slotname, failover, two_phase)
 #define walrcv_get_backend_pid(conn) \
 	WalReceiverFunctions->walrcv_get_backend_pid(conn)
 #define walrcv_exec(conn, exec, nRetTypes, retTypes) \
diff --git a/src/include/replication/worker_internal.h b/src/include/replication/worker_internal.h
index 515aefd519..d5428263c1 100644
--- a/src/include/replication/worker_internal.h
+++ b/src/include/replication/worker_internal.h
@@ -246,6 +246,7 @@ extern bool logicalrep_worker_launch(LogicalRepWorkerType wtype,
 									 Oid userid, Oid relid,
 									 dsm_handle subworker_dsm);
 extern void logicalrep_worker_stop(Oid subid, Oid relid);
+extern void logicalrep_workers_stop(Oid subid);
 extern void logicalrep_pa_worker_stop(ParallelApplyWorkerInfo *winfo);
 extern void logicalrep_worker_wakeup(Oid subid, Oid relid);
 extern void logicalrep_worker_wakeup_ptr(LogicalRepWorker *worker);
diff --git a/src/test/regress/expected/subscription.out b/src/test/regress/expected/subscription.out
index 0f2a25cdc1..51fa4b9690 100644
--- a/src/test/regress/expected/subscription.out
+++ b/src/test/regress/expected/subscription.out
@@ -377,10 +377,7 @@ HINT:  To initiate replication, you must manually create the replication slot, e
  regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | p                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
---fail - alter of two_phase option not supported.
-ALTER SUBSCRIPTION regress_testsub SET (two_phase = false);
-ERROR:  unrecognized subscription parameter: "two_phase"
--- but can alter streaming when two_phase enabled
+-- We can alter streaming when two_phase enabled
 ALTER SUBSCRIPTION regress_testsub SET (streaming = true);
 \dRs+
                                                                                                                 List of subscriptions
diff --git a/src/test/regress/sql/subscription.sql b/src/test/regress/sql/subscription.sql
index 3e5ba4cb8c..a3886d79ca 100644
--- a/src/test/regress/sql/subscription.sql
+++ b/src/test/regress/sql/subscription.sql
@@ -256,10 +256,7 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUBLICATION testpub WITH (connect = false, two_phase = true);
 
 \dRs+
---fail - alter of two_phase option not supported.
-ALTER SUBSCRIPTION regress_testsub SET (two_phase = false);
-
--- but can alter streaming when two_phase enabled
+-- We can alter streaming when two_phase enabled
 ALTER SUBSCRIPTION regress_testsub SET (streaming = true);
 
 \dRs+
diff --git a/src/test/subscription/t/021_twophase.pl b/src/test/subscription/t/021_twophase.pl
index 9437cd4c3b..0436cafdb8 100644
--- a/src/test/subscription/t/021_twophase.pl
+++ b/src/test/subscription/t/021_twophase.pl
@@ -367,6 +367,75 @@ $result =
   $node_subscriber->safe_psql('postgres', "SELECT count(*) FROM tab_copy;");
 is($result, qq(2), 'replicated data in subscriber table');
 
+# Clean up
+$node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub");
+
+###############################
+# Disable the subscription and alter it to two_phase = false,
+# then verify that the altered subscription reflects the two_phase option.
+###############################
+
+# Alter subscription two_phase to false
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy DISABLE");
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = false)");
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy ENABLE");
+
+# Wait for subscription startup
+$node_subscriber->wait_for_subscription_sync($node_publisher, $appname_copy);
+
+# Make sure that the two-phase is disabled on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT subtwophasestate FROM pg_subscription WHERE subname = 'tap_sub_copy';"
+);
+is($result, qq(d), 'two-phase should be disabled');
+
+# Now do a prepare on the publisher and make sure that it is not replicated.
+$node_publisher->safe_psql(
+	'postgres', qq{
+    BEGIN;
+    INSERT INTO tab_copy VALUES (100);
+    PREPARE TRANSACTION 'newgid';
+	});
+
+# Wait for the subscriber to catchup
+$node_publisher->wait_for_catchup($appname_copy);
+
+# Make sure there are no prepared transactions on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT count(*) FROM pg_prepared_xacts;");
+is($result, qq(0), 'should be no prepared transactions on subscriber');
+
+# Now commit the insert and verify that it IS replicated
+$node_publisher->safe_psql('postgres', "COMMIT PREPARED 'newgid';");
+
+# Wait for the subscriber to catchup
+$node_publisher->wait_for_catchup($appname_copy);
+
+# Make sure that the committed transaction is replicated.
+$result =
+  $node_subscriber->safe_psql('postgres', "SELECT count(*) FROM tab_copy;");
+is($result, qq(3), 'replicated data in subscriber table');
+
+# Alter subscription two_phase to true
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy DISABLE");
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = true)");
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy ENABLE");
+
+# Wait for subscription startup
+$node_subscriber->wait_for_subscription_sync($node_publisher, $appname_copy);
+
+# Make sure that the two-phase is enabled on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT subtwophasestate FROM pg_subscription WHERE subname = 'tap_sub_copy';"
+);
+is($result, qq(e), 'two-phase should be enabled');
+
 $node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub_copy;");
 $node_publisher->safe_psql('postgres', "DROP PUBLICATION tap_pub_copy;");
 
@@ -374,8 +443,6 @@ $node_publisher->safe_psql('postgres', "DROP PUBLICATION tap_pub_copy;");
 # check all the cleanup
 ###############################
 
-$node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub");
-
 $result = $node_subscriber->safe_psql('postgres',
 	"SELECT count(*) FROM pg_subscription");
 is($result, qq(0), 'check subscription was dropped on subscriber');
-- 
2.43.0

From d22eef501989c96d7a49b9f7fd8b60f3e749c22d Mon Sep 17 00:00:00 2001
From: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Date: Wed, 17 Apr 2024 06:18:23 +0000
Subject: [PATCH v14 2/4] Alter slot option two_phase only when altering "true"
 to "false"
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Since the two_phase option is controlled by both the publisher (as a slot option)
and the subscriber (as a subscription option), the slot option must also be
modified.

Regarding the false->true case, the backend process alters the subtwophase to
LOGICALREP_TWOPHASE_STATE_PENDING once. After the subscription is enabled, a new
logical replication worker requests to change the two_phase option of its slot
from pending to true after the initial data synchronization is done. The code
path is the same as the case in which two_phase is initially set to true, so
there is no need to do something remarkable. However, for the true->false case,
the backend must connect to the publisher and expressly change the parameter
because the apply worker does not alter the option to false. Because this
operation cannot be rolled back, altering the two_phase parameter from "true"
to "false" within a transaction is prohibited.
---
 doc/src/sgml/ref/alter_subscription.sgml      |  2 +-
 src/backend/commands/subscriptioncmds.c       | 43 ++++++--
 .../libpqwalreceiver/libpqwalreceiver.c       | 23 +++--
 src/include/replication/walreceiver.h         |  5 +-
 src/test/subscription/meson.build             |  1 +
 src/test/subscription/t/099_twophase_added.pl | 99 +++++++++++++++++++
 6 files changed, 157 insertions(+), 16 deletions(-)
 create mode 100644 src/test/subscription/t/099_twophase_added.pl

diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index 0b23df1b77..475a42a2e3 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -70,7 +70,7 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
    <command>ALTER SUBSCRIPTION ... {SET|ADD|DROP} PUBLICATION ...</command>
    with <literal>refresh</literal> option as <literal>true</literal>,
    <command>ALTER SUBSCRIPTION ... SET (failover = true|false)</command> and
-   <command>ALTER SUBSCRIPTION ... SET (two_phase = true|false)</command>
+   <command>ALTER SUBSCRIPTION ... SET (two_phase = off)</command>
    cannot be executed inside a transaction block.
 
    These commands also cannot be executed when the subscription has
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index e925158a4d..996ea6b6de 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -1097,6 +1097,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 	Form_pg_subscription form;
 	bits32		supported_opts;
 	SubOpts		opts = {0};
+	bool		update_failover;
+	bool		update_two_phase;
 
 	rel = table_open(SubscriptionRelationId, RowExclusiveLock);
 
@@ -1187,10 +1189,25 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 								 errhint("Resolve these transactions and try again")));
 
 					/*
-					 * The changed two_phase option of the slot can't be
-					 * rolled back.
+					 * Altering the parameter from "true" to "false" within a
+					 * transaction is prohibited. Since the apply worker does
+					 * not alter the slot option to false, the backend must
+					 * connect to the publisher and expressly change the
+					 * parameter.
+					 *
+					 * There is no need to do something remarkable regarding
+					 * the "false" to "true" case; the backend process alters
+					 * subtwophase to LOGICALREP_TWOPHASE_STATE_PENDING once.
+					 * After the subscription is enabled, a new logical
+					 * replication worker requests to change the two_phase
+					 * option of its slot from pending to true when the
+					 * initial data synchronization is done. The code path is
+					 * the same as the case in which two_phase is initially
+					 * set to true.
 					 */
-					PreventInTransactionBlock(isTopLevel, "ALTER SUBSCRIPTION ... SET (two_phase)");
+					if (!opts.twophase)
+						PreventInTransactionBlock(isTopLevel,
+												  "ALTER SUBSCRIPTION ... SET (two_phase = false)");
 
 					/* Change system catalog acoordingly */
 					values[Anum_pg_subscription_subtwophasestate - 1] =
@@ -1548,14 +1565,24 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 	}
 
 	/*
-	 * Try to acquire the connection necessary for altering slot.
+	 * Check the need to alter the replication slot. Failover and two_phase
+	 * options are controlled by both the publisher (as a slot option) and the
+	 * subscriber (as a subscription option). The slot option must be altered
+	 * only when changing "true" to "false". The reason has already been
+	 * described in the ALTER_SUBSCRIPTION_OPTIONS section of this function.
+	 */
+	update_failover = replaces[Anum_pg_subscription_subfailover - 1];
+	update_two_phase = (replaces[Anum_pg_subscription_subtwophasestate - 1] &&
+						!opts.twophase);
+
+	/*
+	 * Try to acquire the connection necessary for altering slot, if needed.
 	 *
 	 * This has to be at the end because otherwise if there is an error while
 	 * doing the database operations we won't be able to rollback altered
 	 * slot.
 	 */
-	if (replaces[Anum_pg_subscription_subfailover - 1] ||
-		replaces[Anum_pg_subscription_subtwophasestate - 1])
+	if (update_failover || update_two_phase)
 	{
 		bool		must_use_password;
 		char	   *err;
@@ -1575,7 +1602,9 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 
 		PG_TRY();
 		{
-			walrcv_alter_slot(wrconn, sub->slotname, opts.failover, opts.twophase);
+			walrcv_alter_slot(wrconn, sub->slotname,
+							  update_failover ? &opts.failover : NULL,
+							  update_two_phase ? &opts.twophase : NULL);
 		}
 		PG_FINALLY();
 		{
diff --git a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
index 2f035a0c3c..07dfec947d 100644
--- a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
+++ b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
@@ -80,7 +80,7 @@ static char *libpqrcv_create_slot(WalReceiverConn *conn,
 								  CRSSnapshotAction snapshot_action,
 								  XLogRecPtr *lsn);
 static void libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-								bool failover, bool two_phase);
+								const bool *failover, const bool *two_phase);
 static pid_t libpqrcv_get_backend_pid(WalReceiverConn *conn);
 static WalRcvExecResult *libpqrcv_exec(WalReceiverConn *conn,
 									   const char *query,
@@ -1121,16 +1121,27 @@ libpqrcv_create_slot(WalReceiverConn *conn, const char *slotname,
  */
 static void
 libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-					bool failover, bool two_phase)
+					const bool *failover, const bool *two_phase)
 {
 	StringInfoData cmd;
 	PGresult   *res;
 
 	initStringInfo(&cmd);
-	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( FAILOVER %s, TWO_PHASE %s )",
-					 quote_identifier(slotname),
-					 failover ? "true" : "false",
-					 two_phase ? "true" : "false");
+	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( ",
+					 quote_identifier(slotname));
+
+	if (failover)
+		appendStringInfo(&cmd, "FAILOVER %s",
+						 *failover ? "true" : "false");
+
+	if (failover && two_phase)
+		appendStringInfo(&cmd, ", ");
+
+	if (two_phase)
+		appendStringInfo(&cmd, "TWO_PHASE %s",
+						 *two_phase ? "true" : "false");
+
+	appendStringInfoString(&cmd, " );");
 
 	res = libpqrcv_PQexec(conn->streamConn, cmd.data);
 	pfree(cmd.data);
diff --git a/src/include/replication/walreceiver.h b/src/include/replication/walreceiver.h
index 31fa1257ec..7ffa5a58b3 100644
--- a/src/include/replication/walreceiver.h
+++ b/src/include/replication/walreceiver.h
@@ -377,8 +377,9 @@ typedef char *(*walrcv_create_slot_fn) (WalReceiverConn *conn,
  */
 typedef void (*walrcv_alter_slot_fn) (WalReceiverConn *conn,
 									  const char *slotname,
-									  bool failover,
-									  bool two_phase);
+									  const bool *failover,
+									  const bool *two_phase);
+
 
 /*
  * walrcv_get_backend_pid_fn
diff --git a/src/test/subscription/meson.build b/src/test/subscription/meson.build
index c591cd7d61..b4bd522c3d 100644
--- a/src/test/subscription/meson.build
+++ b/src/test/subscription/meson.build
@@ -40,6 +40,7 @@ tests += {
       't/031_column_list.pl',
       't/032_subscribe_use_index.pl',
       't/033_run_as_table_owner.pl',
+      't/099_twophase_added.pl',
       't/100_bugs.pl',
     ],
   },
diff --git a/src/test/subscription/t/099_twophase_added.pl b/src/test/subscription/t/099_twophase_added.pl
new file mode 100644
index 0000000000..1124f7fa00
--- /dev/null
+++ b/src/test/subscription/t/099_twophase_added.pl
@@ -0,0 +1,99 @@
+# Copyright (c) 2024, PostgreSQL Global Development Group
+
+# Additional tests for altering two_phase option
+use strict;
+use warnings FATAL => 'all';
+use PostgreSQL::Test::Cluster;
+use PostgreSQL::Test::Utils;
+use Test::More;
+
+# Initialize publisher node
+my $node_publisher = PostgreSQL::Test::Cluster->new('publisher');
+$node_publisher->init(allows_streaming => 'logical');
+$node_publisher->append_conf('postgresql.conf',
+	qq(max_prepared_transactions = 10));
+$node_publisher->start;
+
+# Create subscriber node
+my $node_subscriber = PostgreSQL::Test::Cluster->new('subscriber');
+$node_subscriber->init;
+$node_subscriber->append_conf(
+	'postgresql.conf',
+	qq(max_prepared_transactions = 10
+	log_min_messages = debug1));
+$node_subscriber->start;
+
+# Define tables on both nodes
+$node_publisher->safe_psql('postgres',
+	"CREATE TABLE tab_full (a int PRIMARY KEY);");
+$node_subscriber->safe_psql('postgres',
+	"CREATE TABLE tab_full (a int PRIMARY KEY)");
+
+# Setup logical replication, with two_phase = "false"
+my $publisher_connstr = $node_publisher->connstr . ' dbname=postgres';
+$node_publisher->safe_psql('postgres',
+	"CREATE PUBLICATION pub FOR ALL TABLES");
+
+my $log_offset = -s $node_subscriber->logfile;
+
+$node_subscriber->safe_psql(
+	'postgres', "
+	CREATE SUBSCRIPTION regress_sub
+	CONNECTION '$publisher_connstr' PUBLICATION pub
+	WITH (two_phase = false, copy_data = false, failover = false)");
+
+# Verify the started worker recognized two_phase was disabled
+$node_subscriber->wait_for_log(
+	'logical replication apply worker for subscription "regress_sub" two_phase is DISABLED',
+	$log_offset);
+
+#####################
+# Check the case that prepared transactions exist on the publisher node.
+#
+# Since the two_phase is "false", then normally, this PREPARE will do nothing
+# until the COMMIT PREPARED, but in this test, we toggle the two_phase to
+# "true" again before the COMMIT PREPARED happens.
+
+# Prepare a transaction to insert some tuples into the table
+$node_publisher->safe_psql(
+	'postgres', "
+	BEGIN;
+	INSERT INTO tab_full VALUES (generate_series(1, 5));
+	PREPARE TRANSACTION 'test_prepared_tab_full';");
+
+$node_publisher->wait_for_catchup('regress_sub');
+
+# Verify the prepared transaction is not yet replicated to the subscriber
+# because two_phase is set to "false".
+my $result = $node_subscriber->safe_psql('postgres',
+	"SELECT count(*) FROM pg_prepared_xacts;");
+is($result, q(0), "transaction is not prepared on subscriber");
+
+$log_offset = -s $node_subscriber->logfile;
+
+# Toggle the two_phase to "true" *before* the COMMIT PREPARED. Since we are the
+# special path for the case where both two_phase and failover are altered, it
+# is also set to "true".
+$node_subscriber->safe_psql(
+	'postgres', "
+    ALTER SUBSCRIPTION regress_sub DISABLE;
+    ALTER SUBSCRIPTION regress_sub SET (two_phase = true, failover = true);
+    ALTER SUBSCRIPTION regress_sub ENABLE;");
+
+# Verify the started worker recognized two_phase was enabled
+$node_subscriber->wait_for_log(
+	'logical replication apply worker for subscription "regress_sub" two_phase is ENABLED',
+	$log_offset);
+
+# And do COMMIT PREPARED the prepared transaction
+$node_publisher->safe_psql('postgres',
+	"COMMIT PREPARED 'test_prepared_tab_full';");
+$node_publisher->wait_for_catchup('regress_sub');
+
+# Verify inserted tuples are replicated
+$result =
+  $node_subscriber->safe_psql('postgres', "SELECT count(*) FROM tab_full;");
+is($result, q(5),
+	"prepared transactions done before altering can be replicated");
+
+done_testing();
-- 
2.43.0

From be5727394811456e5b1dc3e38c6faccfc390452b Mon Sep 17 00:00:00 2001
From: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Date: Mon, 8 Apr 2024 12:39:12 +0000
Subject: [PATCH v14 3/4] Abort prepared transactions while altering two_phase
 to off

If we alter the two_phase parameter from "on" to "off" and there are prepared
transactions on the subscriber, they won't be resolved. To avoid this issue, we
allow the backend to abort all prepared transactions while altering the
subscription.
---
 doc/src/sgml/ref/alter_subscription.sgml      | 11 ++-
 src/backend/access/transam/twophase.c         | 17 ++---
 src/backend/commands/subscriptioncmds.c       | 75 ++++++++++++-------
 src/include/access/twophase.h                 |  3 +-
 src/test/subscription/t/099_twophase_added.pl | 44 +++++++++++
 5 files changed, 110 insertions(+), 40 deletions(-)

diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index 475a42a2e3..8801f37f0e 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -233,8 +233,6 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>, and
       <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>.
       Only a superuser can set <literal>password_required = false</literal>.
-      The <literal>two_phase</literal> parameter can only be altered when the
-      subscription is disabled.
      </para>
 
      <para>
@@ -256,6 +254,15 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>
       option is enabled.
      </para>
+
+     <para>
+      The <literal>two_phase</literal> parameter can only be altered when the
+      subscription is disabled. When altering the parameter from <literal>true</literal>
+      to <literal>false</literal>, the backend process checks for any incomplete
+      prepared transactions done by the logical replication worker (from when
+      <literal>two_phase</literal> parameter was still <literal>true</literal>)
+      and, if any are found, those are aborted.
+     </para>
     </listitem>
    </varlistentry>
 
diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index 35bce6809d..0be8a15367 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -2719,13 +2719,13 @@ IsTwoPhaseTransactionGidForSubid(Oid subid, char *gid)
 }
 
 /*
- * LookupGXactBySubid
- *		Check if the prepared transaction done by apply worker exists.
+ * GetGidListBySubid
+ *      Get a list of GIDs which is PREPARE'd by the given subscription.
  */
-bool
-LookupGXactBySubid(Oid subid)
+List *
+GetGidListBySubid(Oid subid)
 {
-	bool		found = false;
+	List	   *list = NIL;
 
 	LWLockAcquire(TwoPhaseStateLock, LW_SHARED);
 	for (int i = 0; i < TwoPhaseState->numPrepXacts; i++)
@@ -2735,11 +2735,8 @@ LookupGXactBySubid(Oid subid)
 		/* Ignore not-yet-valid GIDs. */
 		if (gxact->valid &&
 			IsTwoPhaseTransactionGidForSubid(subid, gxact->gid))
-		{
-			found = true;
-			break;
-		}
+			list = lappend(list, pstrdup(gxact->gid));
 	}
 	LWLockRelease(TwoPhaseStateLock);
-	return found;
+	return list;
 }
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index 996ea6b6de..54a2c76f37 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -1177,38 +1177,59 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 					logicalrep_workers_stop(subid);
 
 					/*
-					 * two_phase cannot be disabled if there are any
-					 * uncommitted prepared transactions present.
-					 */
-					if (!opts.twophase &&
-						form->subtwophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
-						LookupGXactBySubid(subid))
-						ereport(ERROR,
-								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-								 errmsg("cannot disable two_phase when uncommitted prepared transactions present"),
-								 errhint("Resolve these transactions and try again")));
-
-					/*
-					 * Altering the parameter from "true" to "false" within a
-					 * transaction is prohibited. Since the apply worker does
-					 * not alter the slot option to false, the backend must
-					 * connect to the publisher and expressly change the
-					 * parameter.
-					 *
-					 * There is no need to do something remarkable regarding
-					 * the "false" to "true" case; the backend process alters
-					 * subtwophase to LOGICALREP_TWOPHASE_STATE_PENDING once.
-					 * After the subscription is enabled, a new logical
-					 * replication worker requests to change the two_phase
-					 * option of its slot from pending to true when the
-					 * initial data synchronization is done. The code path is
-					 * the same as the case in which two_phase is initially
-					 * set to true.
+					 * If two_phase was previously enabled, there is a
+					 * possibility that transactions have already been
+					 * PREPARE'd. They must be checked and rolled back.
 					 */
 					if (!opts.twophase)
+					{
+						List	   *prepared_xacts;
+
+						/*
+						 * Altering the parameter from "true" to "false"
+						 * within a transaction is prohibited. Since the apply
+						 * worker does not alter the slot option to false, the
+						 * backend must connect to the publisher and expressly
+						 * change the parameter.
+						 *
+						 * There is no need to do something remarkable
+						 * regarding the "false" to "true" case; the backend
+						 * process alters subtwophase to
+						 * LOGICALREP_TWOPHASE_STATE_PENDING once. After the
+						 * subscription is enabled, a new logical replication
+						 * worker requests to change the two_phase option of
+						 * its slot from pending to true when the initial data
+						 * synchronization is done. The code path is the same
+						 * as the case in which two_phase is initially
+						 * set to true.
+						 */
 						PreventInTransactionBlock(isTopLevel,
 												  "ALTER SUBSCRIPTION ... SET (two_phase = false)");
 
+						/*
+						 * To prevent prepared transactions from being
+						 * isolated, they must manually be aborted.
+						 */
+						if (sub->twophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
+							(prepared_xacts = GetGidListBySubid(subid)) != NIL)
+						{
+							ereport(WARNING,
+									(errmsg_plural("requested altering to %s but there is prepared transaction done by the subscription",
+												   "requested altering to %s but there are prepared transactions done by the subscription",
+												   list_length(prepared_xacts),
+												   "two_phase = false"),
+									 errdetail_plural("Such a transaction is being rollbacked.",
+													  "Such transactions are being rollbacked.",
+													  list_length(prepared_xacts))));
+
+							/* Abort all listed transactions */
+							foreach_ptr(char, gid, prepared_xacts)
+								FinishPreparedTransaction(gid, false);
+
+							list_free_deep(prepared_xacts);
+						}
+					}
+
 					/* Change system catalog acoordingly */
 					values[Anum_pg_subscription_subtwophasestate - 1] =
 						CharGetDatum(opts.twophase ?
diff --git a/src/include/access/twophase.h b/src/include/access/twophase.h
index d37e06fdee..f7a5cf0c12 100644
--- a/src/include/access/twophase.h
+++ b/src/include/access/twophase.h
@@ -18,6 +18,7 @@
 #include "access/xlogdefs.h"
 #include "datatype/timestamp.h"
 #include "storage/lock.h"
+#include "nodes/pg_list.h"
 
 /*
  * GlobalTransactionData is defined in twophase.c; other places have no
@@ -65,6 +66,6 @@ extern bool LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 
 extern void TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid,
 								   int szgid);
-extern bool LookupGXactBySubid(Oid subid);
+extern List *GetGidListBySubid(Oid subid);
 
 #endif							/* TWOPHASE_H */
diff --git a/src/test/subscription/t/099_twophase_added.pl b/src/test/subscription/t/099_twophase_added.pl
index 1124f7fa00..635daf7a78 100644
--- a/src/test/subscription/t/099_twophase_added.pl
+++ b/src/test/subscription/t/099_twophase_added.pl
@@ -96,4 +96,48 @@ $result =
 is($result, q(5),
 	"prepared transactions done before altering can be replicated");
 
+#####################
+# Check the case that prepared transactions exist on the subscriber node
+#
+# If the two_phase is altering from "true" to "false" and there are prepared
+# transactions on the subscriber, they must be aborted. This test checks it.
+
+# Prepare a transaction to insert some tuples into the table
+$node_publisher->safe_psql(
+	'postgres', "
+	BEGIN;
+	INSERT INTO tab_full VALUES (generate_series(6, 10));
+	PREPARE TRANSACTION 'test_prepared_tab_full';");
+
+$node_publisher->wait_for_catchup('regress_sub');
+
+# Verify the prepared transaction has been replicated to the subscriber because
+# two_phase is set to "true".
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT count(*) FROM pg_prepared_xacts;");
+is($result, q(1), "transaction has been prepared on subscriber");
+
+# Toggle the two_phase to "false" before the COMMIT PREPARED
+$node_subscriber->safe_psql(
+	'postgres', "
+    ALTER SUBSCRIPTION regress_sub DISABLE;
+    ALTER SUBSCRIPTION regress_sub SET (two_phase = false);
+    ALTER SUBSCRIPTION regress_sub ENABLE;");
+
+# Verify any prepared transactions are aborted because two_phase is changed to
+# "false".
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT count(*) FROM pg_prepared_xacts;");
+is($result, q(0), "prepared transaction done by worker is aborted");
+
+# Do COMMIT PREPARED the prepared transaction
+$node_publisher->safe_psql('postgres',
+	"COMMIT PREPARED 'test_prepared_tab_full';");
+$node_publisher->wait_for_catchup('regress_sub');
+
+# Verify inserted tuples are replicated
+$result =
+  $node_subscriber->safe_psql('postgres', "SELECT count(10) FROM tab_full;");
+is($result, q(10), "prepared transactions on publisher can be replicated");
+
 done_testing();
-- 
2.43.0

From 85d2922ab3f3329a8cb4e2975efa930da9bf966d Mon Sep 17 00:00:00 2001
From: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Date: Fri, 19 Apr 2024 11:03:19 +0000
Subject: [PATCH v14 4/4] Add force_alter option for ALTER SUBSCRIPTION ... SET
 command

Previously, all prepared transactions on the standby were rolled back when
toggling two_phase from "true" to "false". However, this operation may not be
expected by users. To ensure users understand what happens, we added the
"force_alter" parameter. When two_phase is toggling to "false", and there are
prepared transactions, they will be aborted only when "force_alter" is set to
true. Otherwise, an ERROR occurs.
---
 doc/src/sgml/catalogs.sgml                    |  12 ++
 doc/src/sgml/ref/alter_subscription.sgml      |  16 +-
 doc/src/sgml/ref/create_subscription.sgml     |  24 +++
 src/backend/catalog/pg_subscription.c         |   1 +
 src/backend/catalog/system_views.sql          |   2 +-
 src/backend/commands/subscriptioncmds.c       |  36 ++++-
 src/bin/pg_dump/pg_dump.c                     |  18 ++-
 src/bin/pg_dump/pg_dump.h                     |   1 +
 src/bin/psql/describe.c                       |   7 +-
 src/include/catalog/pg_subscription.h         |  13 ++
 src/test/regress/expected/subscription.out    | 152 +++++++++---------
 src/test/subscription/t/099_twophase_added.pl |  44 ++++-
 12 files changed, 229 insertions(+), 97 deletions(-)

diff --git a/doc/src/sgml/catalogs.sgml b/doc/src/sgml/catalogs.sgml
index b654fae1b2..bca2f0c77a 100644
--- a/doc/src/sgml/catalogs.sgml
+++ b/doc/src/sgml/catalogs.sgml
@@ -8035,6 +8035,18 @@ SCRAM-SHA-256$<replaceable>&lt;iteration count&gt;</replaceable>:<replaceable>&l
       </para></entry>
      </row>
 
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>subforcealter</structfield> <type>bool</type>
+      </para>
+      <para>
+       If true, then the <link linkend="sql-altersubscription"><command>ALTER SUBSCRIPTION</command></link>
+       can sometimes be forced to proceed instead of giving an error. See
+       <link linkend="sql-createsubscription-params-with-force-alter"><literal>force_alter</literal></link>
+       parameter for details about when this might be useful.
+      </para></entry>
+     </row>
+
      <row>
       <entry role="catalog_table_entry"><para role="column_definition">
        <structfield>subconninfo</structfield> <type>text</type>
diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index 8801f37f0e..ab2cdaeaa3 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -230,8 +230,9 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-password-required"><literal>password_required</literal></link>,
       <link linkend="sql-createsubscription-params-with-run-as-owner"><literal>run_as_owner</literal></link>,
       <link linkend="sql-createsubscription-params-with-origin"><literal>origin</literal></link>,
-      <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>, and
-      <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>.
+      <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>,
+      <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>, and
+      <link linkend="sql-createsubscription-params-with-force-alter"><literal>force_alter</literal></link>
       Only a superuser can set <literal>password_required = false</literal>.
      </para>
 
@@ -257,11 +258,12 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
 
      <para>
       The <literal>two_phase</literal> parameter can only be altered when the
-      subscription is disabled. When altering the parameter from <literal>true</literal>
-      to <literal>false</literal>, the backend process checks for any incomplete
-      prepared transactions done by the logical replication worker (from when
-      <literal>two_phase</literal> parameter was still <literal>true</literal>)
-      and, if any are found, those are aborted.
+      subscription is disabled. Altering the parameter from <literal>true</literal>
+      to <literal>false</literal> will give an error when there are prepared
+      transactions done by the logical replication worker. If you want to alter
+      the parameter forcibly in this case,
+      <link linkend="sql-createsubscription-params-with-force-alter"><literal>force_alter</literal></link>
+      option must be set to <literal>true</literal>.
      </para>
     </listitem>
    </varlistentry>
diff --git a/doc/src/sgml/ref/create_subscription.sgml b/doc/src/sgml/ref/create_subscription.sgml
index 740b7d9421..83ac52f865 100644
--- a/doc/src/sgml/ref/create_subscription.sgml
+++ b/doc/src/sgml/ref/create_subscription.sgml
@@ -428,6 +428,30 @@ CREATE SUBSCRIPTION <replaceable class="parameter">subscription_name</replaceabl
          </para>
         </listitem>
        </varlistentry>
+
+       <varlistentry id="sql-createsubscription-params-with-force-alter">
+        <term><literal>force_alter</literal> (<type>boolean</type>)</term>
+        <listitem>
+         <para>
+          Specifies if the <link linkend="sql-altersubscription"><command>ALTER SUBSCRIPTION</command></link>
+          can be forced to proceed instead of giving an error.
+         </para>
+         <para>
+          There is currently only one scenario where this parameter has any
+          effect: When altering <literal>two_phase</literal> option from
+          <literal>true</literal> to <literal>false</literal> it is possible
+          for there to be incomplete prepared transactions done by the logical
+          replication worker (from when <literal>two_phase</literal> parameter
+          was still <literal>true</literal>). If <literal>force_alter</literal>
+          is <literal>false</literal>, then this will give an error; if
+          <literal>force_alter</literal> is <literal>true</literal>, then the
+          incomplete prepared transactions are aborted and the alter will proceed.
+         </para>
+         <para>
+          The default is <literal>false</literal>.
+         </para>
+        </listitem>
+       </varlistentry>
       </variablelist></para>
 
     </listitem>
diff --git a/src/backend/catalog/pg_subscription.c b/src/backend/catalog/pg_subscription.c
index 9efc9159f2..b568fe3470 100644
--- a/src/backend/catalog/pg_subscription.c
+++ b/src/backend/catalog/pg_subscription.c
@@ -72,6 +72,7 @@ GetSubscription(Oid subid, bool missing_ok)
 	sub->passwordrequired = subform->subpasswordrequired;
 	sub->runasowner = subform->subrunasowner;
 	sub->failover = subform->subfailover;
+	sub->forcealter = subform->subforcealter;
 
 	/* Get conninfo */
 	datum = SysCacheGetAttrNotNull(SUBSCRIPTIONOID,
diff --git a/src/backend/catalog/system_views.sql b/src/backend/catalog/system_views.sql
index 19cabc9a47..b89eacc96b 100644
--- a/src/backend/catalog/system_views.sql
+++ b/src/backend/catalog/system_views.sql
@@ -1355,7 +1355,7 @@ REVOKE ALL ON pg_replication_origin_status FROM public;
 REVOKE ALL ON pg_subscription FROM public;
 GRANT SELECT (oid, subdbid, subskiplsn, subname, subowner, subenabled,
               subbinary, substream, subtwophasestate, subdisableonerr,
-			  subpasswordrequired, subrunasowner, subfailover,
+			  subpasswordrequired, subrunasowner, subfailover, subforcealter,
               subslotname, subsynccommit, subpublications, suborigin)
     ON pg_subscription TO public;
 
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index 54a2c76f37..01fe1ee0aa 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -73,6 +73,7 @@
 #define SUBOPT_FAILOVER				0x00002000
 #define SUBOPT_LSN					0x00004000
 #define SUBOPT_ORIGIN				0x00008000
+#define SUBOPT_FORCE_ALTER			0x00010000
 
 /* check if the 'val' has 'bits' set */
 #define IsSet(val, bits)  (((val) & (bits)) == (bits))
@@ -100,6 +101,7 @@ typedef struct SubOpts
 	bool		failover;
 	char	   *origin;
 	XLogRecPtr	lsn;
+	bool		force_alter;
 } SubOpts;
 
 static List *fetch_table_list(WalReceiverConn *wrconn, List *publications);
@@ -162,6 +164,8 @@ parse_subscription_options(ParseState *pstate, List *stmt_options,
 		opts->failover = false;
 	if (IsSet(supported_opts, SUBOPT_ORIGIN))
 		opts->origin = pstrdup(LOGICALREP_ORIGIN_ANY);
+	if (IsSet(supported_opts, SUBOPT_FORCE_ALTER))
+		opts->force_alter = false;
 
 	/* Parse options */
 	foreach(lc, stmt_options)
@@ -367,6 +371,15 @@ parse_subscription_options(ParseState *pstate, List *stmt_options,
 			opts->specified_opts |= SUBOPT_LSN;
 			opts->lsn = lsn;
 		}
+		else if (IsSet(supported_opts, SUBOPT_FORCE_ALTER) &&
+				 strcmp(defel->defname, "force_alter") == 0)
+		{
+			if (IsSet(opts->specified_opts, SUBOPT_FORCE_ALTER))
+				errorConflictingDefElem(defel, pstate);
+
+			opts->specified_opts |= SUBOPT_FORCE_ALTER;
+			opts->force_alter = defGetBoolean(defel);
+		}
 		else
 			ereport(ERROR,
 					(errcode(ERRCODE_SYNTAX_ERROR),
@@ -604,7 +617,8 @@ CreateSubscription(ParseState *pstate, CreateSubscriptionStmt *stmt,
 					  SUBOPT_SYNCHRONOUS_COMMIT | SUBOPT_BINARY |
 					  SUBOPT_STREAMING | SUBOPT_TWOPHASE_COMMIT |
 					  SUBOPT_DISABLE_ON_ERR | SUBOPT_PASSWORD_REQUIRED |
-					  SUBOPT_RUN_AS_OWNER | SUBOPT_FAILOVER | SUBOPT_ORIGIN);
+					  SUBOPT_RUN_AS_OWNER | SUBOPT_FAILOVER | SUBOPT_ORIGIN |
+					  SUBOPT_FORCE_ALTER);
 	parse_subscription_options(pstate, stmt->options, supported_opts, &opts);
 
 	/*
@@ -711,6 +725,7 @@ CreateSubscription(ParseState *pstate, CreateSubscriptionStmt *stmt,
 	values[Anum_pg_subscription_subpasswordrequired - 1] = BoolGetDatum(opts.passwordrequired);
 	values[Anum_pg_subscription_subrunasowner - 1] = BoolGetDatum(opts.runasowner);
 	values[Anum_pg_subscription_subfailover - 1] = BoolGetDatum(opts.failover);
+	values[Anum_pg_subscription_subforcealter - 1] = BoolGetDatum(opts.force_alter);
 	values[Anum_pg_subscription_subconninfo - 1] =
 		CStringGetTextDatum(conninfo);
 	if (opts.slot_name)
@@ -1150,7 +1165,7 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 								  SUBOPT_DISABLE_ON_ERR |
 								  SUBOPT_PASSWORD_REQUIRED |
 								  SUBOPT_RUN_AS_OWNER | SUBOPT_FAILOVER |
-								  SUBOPT_ORIGIN);
+								  SUBOPT_ORIGIN | SUBOPT_FORCE_ALTER);
 
 				parse_subscription_options(pstate, stmt->options,
 										   supported_opts, &opts);
@@ -1213,6 +1228,23 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 						if (sub->twophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
 							(prepared_xacts = GetGidListBySubid(subid)) != NIL)
 						{
+							bool		raise_error =
+								IsSet(opts.specified_opts, SUBOPT_FORCE_ALTER) ?
+								!opts.force_alter : !sub->forcealter;
+
+							/*
+							 * Abort prepared transactions only if
+							 * 'force_alter' option is true. Otherwise raise
+							 * an ERROR.
+							 */
+							if (raise_error)
+								ereport(ERROR,
+										(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+										 errmsg("cannot alter %s when there are prepared transactions",
+												"two_phase = false"),
+										 errhint("Resolve these transactions or set %s, and then try again.",
+												 "force_alter = true")));
+
 							ereport(WARNING,
 									(errmsg_plural("requested altering to %s but there is prepared transaction done by the subscription",
 												   "requested altering to %s but there are prepared transactions done by the subscription",
diff --git a/src/bin/pg_dump/pg_dump.c b/src/bin/pg_dump/pg_dump.c
index 5426f1177c..85c69a835b 100644
--- a/src/bin/pg_dump/pg_dump.c
+++ b/src/bin/pg_dump/pg_dump.c
@@ -4754,6 +4754,7 @@ getSubscriptions(Archive *fout)
 	int			i_suboriginremotelsn;
 	int			i_subenabled;
 	int			i_subfailover;
+	int			i_subforcealter;
 	int			i,
 				ntups;
 
@@ -4826,10 +4827,17 @@ getSubscriptions(Archive *fout)
 
 	if (fout->remoteVersion >= 170000)
 		appendPQExpBufferStr(query,
-							 " s.subfailover\n");
+							 " s.subfailover,\n");
 	else
 		appendPQExpBuffer(query,
-						  " false AS subfailover\n");
+						  " false AS subfailover,\n");
+
+	if (fout->remoteVersion >= 170000)
+		appendPQExpBufferStr(query,
+							 " s.subforcealter\n");
+	else
+		appendPQExpBuffer(query,
+						  " false AS subforcealter\n");
 
 	appendPQExpBufferStr(query,
 						 "FROM pg_subscription s\n");
@@ -4869,6 +4877,7 @@ getSubscriptions(Archive *fout)
 	i_suboriginremotelsn = PQfnumber(res, "suboriginremotelsn");
 	i_subenabled = PQfnumber(res, "subenabled");
 	i_subfailover = PQfnumber(res, "subfailover");
+	i_subforcealter = PQfnumber(res, "subforcealter");
 
 	subinfo = pg_malloc(ntups * sizeof(SubscriptionInfo));
 
@@ -4915,6 +4924,8 @@ getSubscriptions(Archive *fout)
 			pg_strdup(PQgetvalue(res, i, i_subenabled));
 		subinfo[i].subfailover =
 			pg_strdup(PQgetvalue(res, i, i_subfailover));
+		subinfo[i].subforcealter =
+			pg_strdup(PQgetvalue(res, i, i_subforcealter));
 
 		/* Decide whether we want to dump it */
 		selectDumpableObject(&(subinfo[i].dobj), fout);
@@ -5155,6 +5166,9 @@ dumpSubscription(Archive *fout, const SubscriptionInfo *subinfo)
 	if (strcmp(subinfo->subfailover, "t") == 0)
 		appendPQExpBufferStr(query, ", failover = true");
 
+	if (strcmp(subinfo->subforcealter, "t") == 0)
+		appendPQExpBufferStr(query, ", force_alter = true");
+
 	if (strcmp(subinfo->subsynccommit, "off") != 0)
 		appendPQExpBuffer(query, ", synchronous_commit = %s", fmtId(subinfo->subsynccommit));
 
diff --git a/src/bin/pg_dump/pg_dump.h b/src/bin/pg_dump/pg_dump.h
index 4b2e5870a9..8f5f9d13b9 100644
--- a/src/bin/pg_dump/pg_dump.h
+++ b/src/bin/pg_dump/pg_dump.h
@@ -671,6 +671,7 @@ typedef struct _SubscriptionInfo
 	char	   *suborigin;
 	char	   *suboriginremotelsn;
 	char	   *subfailover;
+	char	   *subforcealter;
 } SubscriptionInfo;
 
 /*
diff --git a/src/bin/psql/describe.c b/src/bin/psql/describe.c
index 7c9a1f234c..abf91a81fa 100644
--- a/src/bin/psql/describe.c
+++ b/src/bin/psql/describe.c
@@ -6539,7 +6539,7 @@ describeSubscriptions(const char *pattern, bool verbose)
 	printQueryOpt myopt = pset.popt;
 	static const bool translate_columns[] = {false, false, false, false,
 		false, false, false, false, false, false, false, false, false, false,
-	false};
+	false, false};
 
 	if (pset.sversion < 100000)
 	{
@@ -6608,6 +6608,11 @@ describeSubscriptions(const char *pattern, bool verbose)
 							  ", subfailover AS \"%s\"\n",
 							  gettext_noop("Failover"));
 
+		if (pset.sversion >= 170000)
+			appendPQExpBuffer(&buf,
+							  ", subforcealter AS \"%s\"\n",
+							  gettext_noop("Force alter"));
+
 		appendPQExpBuffer(&buf,
 						  ",  subsynccommit AS \"%s\"\n"
 						  ",  subconninfo AS \"%s\"\n",
diff --git a/src/include/catalog/pg_subscription.h b/src/include/catalog/pg_subscription.h
index 0aa14ec4a2..deac7aa943 100644
--- a/src/include/catalog/pg_subscription.h
+++ b/src/include/catalog/pg_subscription.h
@@ -98,6 +98,13 @@ CATALOG(pg_subscription,6100,SubscriptionRelationId) BKI_SHARED_RELATION BKI_ROW
 								 * slots) in the upstream database are enabled
 								 * to be synchronized to the standbys. */
 
+	bool		subforcealter;	/* True allows the ALTER SUBSCRIPTION command
+								 * to proceed under conditions that would
+								 * otherwise result in an error. Currently,
+								 * 'force_alter' only has an effect when
+								 * altering the two_phase option from "true"
+								 * to "false". */
+
 #ifdef CATALOG_VARLEN			/* variable-length fields start here */
 	/* Connection string to the publisher */
 	text		subconninfo BKI_FORCE_NOT_NULL;
@@ -151,6 +158,12 @@ typedef struct Subscription
 								 * (i.e. the main slot and the table sync
 								 * slots) in the upstream database are enabled
 								 * to be synchronized to the standbys. */
+	bool		forcealter;		/* True allows the ALTER SUBSCRIPTION command
+								 * to proceed under conditions that would
+								 * otherwise result in an error. Currently,
+								 * 'force_alter' only has an effect when
+								 * altering the two_phase option from "true"
+								 * to "false". */
 	char	   *conninfo;		/* Connection string to the publisher */
 	char	   *slotname;		/* Name of the replication slot */
 	char	   *synccommit;		/* Synchronous commit setting for worker */
diff --git a/src/test/regress/expected/subscription.out b/src/test/regress/expected/subscription.out
index 51fa4b9690..b36fc6b8f7 100644
--- a/src/test/regress/expected/subscription.out
+++ b/src/test/regress/expected/subscription.out
@@ -116,18 +116,18 @@ CREATE SUBSCRIPTION regress_testsub4 CONNECTION 'dbname=regress_doesnotexist' PU
 WARNING:  subscription was created, but is not connected
 HINT:  To initiate replication, you must manually create the replication slot, enable the subscription, and refresh the subscription.
 \dRs+ regress_testsub4
-                                                                                                                 List of subscriptions
-       Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
-------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub4 | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | none   | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                        List of subscriptions
+       Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub4 | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | none   | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub4 SET (origin = any);
 \dRs+ regress_testsub4
-                                                                                                                 List of subscriptions
-       Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
-------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub4 | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                        List of subscriptions
+       Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub4 | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 DROP SUBSCRIPTION regress_testsub3;
@@ -145,10 +145,10 @@ ALTER SUBSCRIPTION regress_testsub CONNECTION 'foobar';
 ERROR:  invalid connection string syntax: missing "=" after "foobar" in connection info string
 
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET PUBLICATION testpub2, testpub3 WITH (refresh = false);
@@ -157,10 +157,10 @@ ALTER SUBSCRIPTION regress_testsub SET (slot_name = 'newname');
 ALTER SUBSCRIPTION regress_testsub SET (password_required = false);
 ALTER SUBSCRIPTION regress_testsub SET (run_as_owner = true);
 \dRs+
-                                                                                                                     List of subscriptions
-      Name       |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |           Conninfo           | Skip LSN 
------------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+------------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | f                 | t             | f        | off                | dbname=regress_doesnotexist2 | 0/0
+                                                                                                                            List of subscriptions
+      Name       |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |           Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+------------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | f                 | t             | f        | f           | off                | dbname=regress_doesnotexist2 | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (password_required = true);
@@ -176,10 +176,10 @@ ERROR:  unrecognized subscription parameter: "create_slot"
 -- ok
 ALTER SUBSCRIPTION regress_testsub SKIP (lsn = '0/12345');
 \dRs+
-                                                                                                                     List of subscriptions
-      Name       |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |           Conninfo           | Skip LSN 
------------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+------------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist2 | 0/12345
+                                                                                                                            List of subscriptions
+      Name       |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |           Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+------------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist2 | 0/12345
 (1 row)
 
 -- ok - with lsn = NONE
@@ -188,10 +188,10 @@ ALTER SUBSCRIPTION regress_testsub SKIP (lsn = NONE);
 ALTER SUBSCRIPTION regress_testsub SKIP (lsn = '0/0');
 ERROR:  invalid WAL location (LSN): 0/0
 \dRs+
-                                                                                                                     List of subscriptions
-      Name       |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |           Conninfo           | Skip LSN 
------------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+------------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist2 | 0/0
+                                                                                                                            List of subscriptions
+      Name       |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |           Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+------------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist2 | 0/0
 (1 row)
 
 BEGIN;
@@ -223,10 +223,10 @@ ALTER SUBSCRIPTION regress_testsub_foo SET (synchronous_commit = foobar);
 ERROR:  invalid value for parameter "synchronous_commit": "foobar"
 HINT:  Available values: local, remote_write, remote_apply, on, off.
 \dRs+
-                                                                                                                       List of subscriptions
-        Name         |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |           Conninfo           | Skip LSN 
----------------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+------------------------------+----------
- regress_testsub_foo | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | t                 | f             | f        | local              | dbname=regress_doesnotexist2 | 0/0
+                                                                                                                              List of subscriptions
+        Name         |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |           Conninfo           | Skip LSN 
+---------------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+------------------------------+----------
+ regress_testsub_foo | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | t                 | f             | f        | f           | local              | dbname=regress_doesnotexist2 | 0/0
 (1 row)
 
 -- rename back to keep the rest simple
@@ -255,19 +255,19 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 WARNING:  subscription was created, but is not connected
 HINT:  To initiate replication, you must manually create the replication slot, enable the subscription, and refresh the subscription.
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | t      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | t      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (binary = false);
 ALTER SUBSCRIPTION regress_testsub SET (slot_name = NONE);
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 DROP SUBSCRIPTION regress_testsub;
@@ -279,27 +279,27 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 WARNING:  subscription was created, but is not connected
 HINT:  To initiate replication, you must manually create the replication slot, enable the subscription, and refresh the subscription.
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | on        | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | on        | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (streaming = parallel);
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | parallel  | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | parallel  | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (streaming = false);
 ALTER SUBSCRIPTION regress_testsub SET (slot_name = NONE);
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 -- fail - publication already exists
@@ -314,10 +314,10 @@ ALTER SUBSCRIPTION regress_testsub ADD PUBLICATION testpub1, testpub2 WITH (refr
 ALTER SUBSCRIPTION regress_testsub ADD PUBLICATION testpub1, testpub2 WITH (refresh = false);
 ERROR:  publication "testpub1" is already in subscription "regress_testsub"
 \dRs+
-                                                                                                                        List of subscriptions
-      Name       |           Owner           | Enabled |         Publication         | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-----------------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub,testpub1,testpub2} | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                               List of subscriptions
+      Name       |           Owner           | Enabled |         Publication         | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-----------------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub,testpub1,testpub2} | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 -- fail - publication used more than once
@@ -332,10 +332,10 @@ ERROR:  publication "testpub3" is not in subscription "regress_testsub"
 -- ok - delete publications
 ALTER SUBSCRIPTION regress_testsub DROP PUBLICATION testpub1, testpub2 WITH (refresh = false);
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 DROP SUBSCRIPTION regress_testsub;
@@ -371,19 +371,19 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 WARNING:  subscription was created, but is not connected
 HINT:  To initiate replication, you must manually create the replication slot, enable the subscription, and refresh the subscription.
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | p                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | p                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 -- We can alter streaming when two_phase enabled
 ALTER SUBSCRIPTION regress_testsub SET (streaming = true);
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | on        | p                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | on        | p                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (slot_name = NONE);
@@ -393,10 +393,10 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 WARNING:  subscription was created, but is not connected
 HINT:  To initiate replication, you must manually create the replication slot, enable the subscription, and refresh the subscription.
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | on        | p                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | on        | p                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (slot_name = NONE);
@@ -409,18 +409,18 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 WARNING:  subscription was created, but is not connected
 HINT:  To initiate replication, you must manually create the replication slot, enable the subscription, and refresh the subscription.
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (disable_on_error = true);
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | t                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | t                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (slot_name = NONE);
diff --git a/src/test/subscription/t/099_twophase_added.pl b/src/test/subscription/t/099_twophase_added.pl
index 635daf7a78..4da8392962 100644
--- a/src/test/subscription/t/099_twophase_added.pl
+++ b/src/test/subscription/t/099_twophase_added.pl
@@ -117,15 +117,43 @@ $result = $node_subscriber->safe_psql('postgres',
 	"SELECT count(*) FROM pg_prepared_xacts;");
 is($result, q(1), "transaction has been prepared on subscriber");
 
-# Toggle the two_phase to "false" before the COMMIT PREPARED
-$node_subscriber->safe_psql(
-	'postgres', "
-    ALTER SUBSCRIPTION regress_sub DISABLE;
-    ALTER SUBSCRIPTION regress_sub SET (two_phase = false);
-    ALTER SUBSCRIPTION regress_sub ENABLE;");
+# Disable the subscription to alter the two_phase option
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION regress_sub DISABLE;");
+
+# Try altering the two_phase option to "false". The command will fail since
+# there is a prepared transaction and the 'force_alter' option is not specified
+# as true.
+my $stdout;
+my $stderr;
+
+($result, $stdout, $stderr) = $node_subscriber->psql('postgres',
+	"ALTER SUBSCRIPTION regress_sub SET (two_phase = false);");
+ok( $stderr =~
+	  /cannot alter two_phase = false when there are prepared transactions/,
+	'ALTER SUBSCRIPTION failed');
+
+# Verify the prepared transaction still exists
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT count(*) FROM pg_prepared_xacts;");
+is($result, q(1), "prepared transaction still exists");
+
+$log_offset = -s $node_subscriber->logfile;
+
+# Alter the two_phase true to false with the force_alter option enabled. This
+# command will succeed after aborting the prepared transaction.
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION regress_sub SET (two_phase = false, force_alter = true);"
+);
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION regress_sub ENABLE;");
+
+# Verify the started worker recognized two_phase was disabled
+$node_subscriber->wait_for_log(
+	'logical replication apply worker for subscription "regress_sub" two_phase is DISABLED',
+	$log_offset);
 
-# Verify any prepared transactions are aborted because two_phase is changed to
-# "false".
+# # Verify the prepared transaction was aborted
 $result = $node_subscriber->safe_psql('postgres',
 	"SELECT count(*) FROM pg_prepared_xacts;");
 is($result, q(0), "prepared transaction done by worker is aborted");
-- 
2.43.0

From 89537a5c41b58c3b2ffcc29cf665adde3ead9cd8 Mon Sep 17 00:00:00 2001
From: Ajin Cherian <ajinc@fast.au.fujitsu.com>
Date: Fri, 5 Apr 2024 06:47:18 -0400
Subject: [PATCH v15 1/4] Allow altering of two_phase option of a SUBSCRIPTION

This patch allows the user to alter the 'two_phase' option of a subscriber provided no
uncommitted prepared transactions are pending on that subscription.

Author: Cherian Ajin, Hayato Kuroda
---
 doc/src/sgml/ref/alter_subscription.sgml      | 12 ++-
 src/backend/access/transam/twophase.c         | 62 ++++++++++++++
 src/backend/commands/subscriptioncmds.c       | 82 ++++++++++++++-----
 .../libpqwalreceiver/libpqwalreceiver.c       |  9 +-
 src/backend/replication/logical/launcher.c    | 12 ++-
 src/backend/replication/logical/worker.c      | 25 +-----
 src/backend/replication/slot.c                | 18 +++-
 src/backend/replication/walsender.c           | 18 +++-
 src/bin/psql/tab-complete.c                   |  2 +-
 src/include/access/twophase.h                 |  5 ++
 src/include/replication/slot.h                |  3 +-
 src/include/replication/walreceiver.h         | 11 +--
 src/include/replication/worker_internal.h     |  3 +-
 src/test/regress/expected/subscription.out    |  5 +-
 src/test/regress/sql/subscription.sql         |  5 +-
 src/test/subscription/t/021_twophase.pl       | 77 ++++++++++++++++-
 16 files changed, 273 insertions(+), 76 deletions(-)

diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index 476f195622..0b23df1b77 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -68,8 +68,9 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
   <para>
    Commands <command>ALTER SUBSCRIPTION ... REFRESH PUBLICATION</command>,
    <command>ALTER SUBSCRIPTION ... {SET|ADD|DROP} PUBLICATION ...</command>
-   with <literal>refresh</literal> option as <literal>true</literal> and
-   <command>ALTER SUBSCRIPTION ... SET (failover = true|false)</command>
+   with <literal>refresh</literal> option as <literal>true</literal>,
+   <command>ALTER SUBSCRIPTION ... SET (failover = true|false)</command> and
+   <command>ALTER SUBSCRIPTION ... SET (two_phase = true|false)</command>
    cannot be executed inside a transaction block.
 
    These commands also cannot be executed when the subscription has
@@ -228,9 +229,12 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-disable-on-error"><literal>disable_on_error</literal></link>,
       <link linkend="sql-createsubscription-params-with-password-required"><literal>password_required</literal></link>,
       <link linkend="sql-createsubscription-params-with-run-as-owner"><literal>run_as_owner</literal></link>,
-      <link linkend="sql-createsubscription-params-with-origin"><literal>origin</literal></link>, and
-      <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>.
+      <link linkend="sql-createsubscription-params-with-origin"><literal>origin</literal></link>,
+      <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>, and
+      <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>.
       Only a superuser can set <literal>password_required = false</literal>.
+      The <literal>two_phase</literal> parameter can only be altered when the
+      subscription is disabled.
      </para>
 
      <para>
diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index 9a8257fcaf..35bce6809d 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -2681,3 +2681,65 @@ LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 	LWLockRelease(TwoPhaseStateLock);
 	return found;
 }
+
+/*
+ * TwoPhaseTransactionGid
+ *		Form the prepared transaction GID for two_phase transactions.
+ *
+ * Return the GID in the supplied buffer.
+ */
+void
+TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid, int szgid)
+{
+	Assert(subid != InvalidRepOriginId);
+
+	if (!TransactionIdIsValid(xid))
+		ereport(ERROR,
+				(errcode(ERRCODE_PROTOCOL_VIOLATION),
+				 errmsg_internal("invalid two-phase transaction ID")));
+
+	snprintf(gid, szgid, "pg_gid_%u_%u", subid, xid);
+}
+
+/*
+ * IsTwoPhaseTransactionGidForSubid
+ *		Check whether the given GID (as formed by TwoPhaseTransactionGid) is
+ *		for the specified 'subid'.
+ */
+static bool
+IsTwoPhaseTransactionGidForSubid(Oid subid, char *gid)
+{
+	int			ret;
+	Oid			subid_written;
+	TransactionId xid;
+
+	ret = sscanf(gid, "pg_gid_%u_%u", &subid_written, &xid);
+
+	return (ret == 2 && subid == subid_written);
+}
+
+/*
+ * LookupGXactBySubid
+ *		Check if the prepared transaction done by apply worker exists.
+ */
+bool
+LookupGXactBySubid(Oid subid)
+{
+	bool		found = false;
+
+	LWLockAcquire(TwoPhaseStateLock, LW_SHARED);
+	for (int i = 0; i < TwoPhaseState->numPrepXacts; i++)
+	{
+		GlobalTransaction gxact = TwoPhaseState->prepXacts[i];
+
+		/* Ignore not-yet-valid GIDs. */
+		if (gxact->valid &&
+			IsTwoPhaseTransactionGidForSubid(subid, gxact->gid))
+		{
+			found = true;
+			break;
+		}
+	}
+	LWLockRelease(TwoPhaseStateLock);
+	return found;
+}
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index e407428dbc..1d57f12942 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -16,6 +16,7 @@
 
 #include "access/htup_details.h"
 #include "access/table.h"
+#include "access/twophase.h"
 #include "access/xact.h"
 #include "catalog/catalog.h"
 #include "catalog/dependency.h"
@@ -259,21 +260,9 @@ parse_subscription_options(ParseState *pstate, List *stmt_options,
 			opts->specified_opts |= SUBOPT_STREAMING;
 			opts->streaming = defGetStreamingMode(defel);
 		}
-		else if (strcmp(defel->defname, "two_phase") == 0)
+		else if (IsSet(supported_opts, SUBOPT_TWOPHASE_COMMIT) &&
+				 strcmp(defel->defname, "two_phase") == 0)
 		{
-			/*
-			 * Do not allow toggling of two_phase option. Doing so could cause
-			 * missing of transactions and lead to an inconsistent replica.
-			 * See comments atop worker.c
-			 *
-			 * Note: Unsupported twophase indicates that this call originated
-			 * from AlterSubscription.
-			 */
-			if (!IsSet(supported_opts, SUBOPT_TWOPHASE_COMMIT))
-				ereport(ERROR,
-						(errcode(ERRCODE_SYNTAX_ERROR),
-						 errmsg("unrecognized subscription parameter: \"%s\"", defel->defname)));
-
 			if (IsSet(opts->specified_opts, SUBOPT_TWOPHASE_COMMIT))
 				errorConflictingDefElem(defel, pstate);
 
@@ -1143,7 +1132,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 			{
 				supported_opts = (SUBOPT_SLOT_NAME |
 								  SUBOPT_SYNCHRONOUS_COMMIT | SUBOPT_BINARY |
-								  SUBOPT_STREAMING | SUBOPT_DISABLE_ON_ERR |
+								  SUBOPT_STREAMING | SUBOPT_TWOPHASE_COMMIT |
+								  SUBOPT_DISABLE_ON_ERR |
 								  SUBOPT_PASSWORD_REQUIRED |
 								  SUBOPT_RUN_AS_OWNER | SUBOPT_FAILOVER |
 								  SUBOPT_ORIGIN);
@@ -1151,6 +1141,59 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 				parse_subscription_options(pstate, stmt->options,
 										   supported_opts, &opts);
 
+				if (IsSet(opts.specified_opts, SUBOPT_TWOPHASE_COMMIT))
+				{
+					/*
+					 * Do not allow changing the two_phase option if the
+					 * subscription is enabled. This is because the two_phase
+					 * option of the slot on the publisher cannot be modified
+					 * if the slot is currently acquired by the apply worker.
+					 */
+					if (form->subenabled)
+						ereport(ERROR,
+								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+								 errmsg("cannot set %s for enabled subscription",
+										"two_phase")));
+
+					/*
+					 * Workers may still survive even if the subscription has
+					 * been disabled. They may read the pg_subscription
+					 * catalog and detect that the twophase parameter is
+					 * updated, which causes the assertion failure. Ensure
+					 * workers have already been exited to avoid it.
+					 */
+					if (logicalrep_workers_find(subid, true, true))
+						ereport(ERROR,
+								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+								 errmsg("cannot alter two_phase when logical replication worker is still running"),
+								 errhint("Wait certain time and try again.")));
+
+					/*
+					 * two_phase cannot be disabled if there are any
+					 * uncommitted prepared transactions present.
+					 */
+					if (!opts.twophase &&
+						form->subtwophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
+						LookupGXactBySubid(subid))
+						ereport(ERROR,
+								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+								 errmsg("cannot disable two_phase when uncommitted prepared transactions present"),
+								 errhint("Resolve these transactions and try again")));
+
+					/*
+					 * The changed two_phase option of the slot can't be
+					 * rolled back.
+					 */
+					PreventInTransactionBlock(isTopLevel, "ALTER SUBSCRIPTION ... SET (two_phase)");
+
+					/* Change system catalog acoordingly */
+					values[Anum_pg_subscription_subtwophasestate - 1] =
+						CharGetDatum(opts.twophase ?
+									 LOGICALREP_TWOPHASE_STATE_PENDING :
+									 LOGICALREP_TWOPHASE_STATE_DISABLED);
+					replaces[Anum_pg_subscription_subtwophasestate - 1] = true;
+				}
+
 				if (IsSet(opts.specified_opts, SUBOPT_SLOT_NAME))
 				{
 					/*
@@ -1505,7 +1548,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 	 * doing the database operations we won't be able to rollback altered
 	 * slot.
 	 */
-	if (replaces[Anum_pg_subscription_subfailover - 1])
+	if (replaces[Anum_pg_subscription_subfailover - 1] ||
+		replaces[Anum_pg_subscription_subtwophasestate - 1])
 	{
 		bool		must_use_password;
 		char	   *err;
@@ -1525,7 +1569,7 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 
 		PG_TRY();
 		{
-			walrcv_alter_slot(wrconn, sub->slotname, opts.failover);
+			walrcv_alter_slot(wrconn, sub->slotname, opts.failover, opts.twophase);
 		}
 		PG_FINALLY();
 		{
@@ -1672,9 +1716,7 @@ DropSubscription(DropSubscriptionStmt *stmt, bool isTopLevel)
 	 * New workers won't be started because we hold an exclusive lock on the
 	 * subscription till the end of the transaction.
 	 */
-	LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
-	subworkers = logicalrep_workers_find(subid, false);
-	LWLockRelease(LogicalRepWorkerLock);
+	subworkers = logicalrep_workers_find(subid, false, true);
 	foreach(lc, subworkers)
 	{
 		LogicalRepWorker *w = (LogicalRepWorker *) lfirst(lc);
diff --git a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
index 02f12f2921..2f035a0c3c 100644
--- a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
+++ b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
@@ -80,7 +80,7 @@ static char *libpqrcv_create_slot(WalReceiverConn *conn,
 								  CRSSnapshotAction snapshot_action,
 								  XLogRecPtr *lsn);
 static void libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-								bool failover);
+								bool failover, bool two_phase);
 static pid_t libpqrcv_get_backend_pid(WalReceiverConn *conn);
 static WalRcvExecResult *libpqrcv_exec(WalReceiverConn *conn,
 									   const char *query,
@@ -1121,15 +1121,16 @@ libpqrcv_create_slot(WalReceiverConn *conn, const char *slotname,
  */
 static void
 libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-					bool failover)
+					bool failover, bool two_phase)
 {
 	StringInfoData cmd;
 	PGresult   *res;
 
 	initStringInfo(&cmd);
-	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( FAILOVER %s )",
+	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( FAILOVER %s, TWO_PHASE %s )",
 					 quote_identifier(slotname),
-					 failover ? "true" : "false");
+					 failover ? "true" : "false",
+					 two_phase ? "true" : "false");
 
 	res = libpqrcv_PQexec(conn->streamConn, cmd.data);
 	pfree(cmd.data);
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 27c3a91fb7..45744b771f 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -272,12 +272,15 @@ logicalrep_worker_find(Oid subid, Oid relid, bool only_running)
  * the subscription, instead of just one.
  */
 List *
-logicalrep_workers_find(Oid subid, bool only_running)
+logicalrep_workers_find(Oid subid, bool only_running, bool require_lock)
 {
 	int			i;
 	List	   *res = NIL;
 
-	Assert(LWLockHeldByMe(LogicalRepWorkerLock));
+	if (require_lock)
+		LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
+	else
+		Assert(LWLockHeldByMe(LogicalRepWorkerLock));
 
 	/* Search for attached worker for a given subscription id. */
 	for (i = 0; i < max_logical_replication_workers; i++)
@@ -288,6 +291,9 @@ logicalrep_workers_find(Oid subid, bool only_running)
 			res = lappend(res, w);
 	}
 
+	if (require_lock)
+		LWLockRelease(LogicalRepWorkerLock);
+
 	return res;
 }
 
@@ -759,7 +765,7 @@ logicalrep_worker_detach(void)
 
 		LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
 
-		workers = logicalrep_workers_find(MyLogicalRepWorker->subid, true);
+		workers = logicalrep_workers_find(MyLogicalRepWorker->subid, true, false);
 		foreach(lc, workers)
 		{
 			LogicalRepWorker *w = (LogicalRepWorker *) lfirst(lc);
diff --git a/src/backend/replication/logical/worker.c b/src/backend/replication/logical/worker.c
index 3b285894db..33bfeb1fb2 100644
--- a/src/backend/replication/logical/worker.c
+++ b/src/backend/replication/logical/worker.c
@@ -401,9 +401,6 @@ static void apply_handle_tuple_routing(ApplyExecutionData *edata,
 									   LogicalRepTupleData *newtup,
 									   CmdType operation);
 
-/* Compute GID for two_phase transactions */
-static void TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid, int szgid);
-
 /* Functions for skipping changes */
 static void maybe_start_skipping_changes(XLogRecPtr finish_lsn);
 static void stop_skipping_changes(void);
@@ -3911,7 +3908,7 @@ maybe_reread_subscription(void)
 	/* !slotname should never happen when enabled is true. */
 	Assert(newsub->slotname);
 
-	/* two-phase should not be altered */
+	/* two-phase cannot be altered while the worker exists */
 	Assert(newsub->twophasestate == MySubscription->twophasestate);
 
 	/*
@@ -4396,24 +4393,6 @@ cleanup_subxact_info()
 	subxact_data.nsubxacts_max = 0;
 }
 
-/*
- * Form the prepared transaction GID for two_phase transactions.
- *
- * Return the GID in the supplied buffer.
- */
-static void
-TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid, int szgid)
-{
-	Assert(subid != InvalidRepOriginId);
-
-	if (!TransactionIdIsValid(xid))
-		ereport(ERROR,
-				(errcode(ERRCODE_PROTOCOL_VIOLATION),
-				 errmsg_internal("invalid two-phase transaction ID")));
-
-	snprintf(gid, szgid, "pg_gid_%u_%u", subid, xid);
-}
-
 /*
  * Common function to run the apply loop with error handling. Disable the
  * subscription, if necessary.
@@ -5013,7 +4992,7 @@ AtEOXact_LogicalRepWorkers(bool isCommit)
 			List	   *workers;
 			ListCell   *lc2;
 
-			workers = logicalrep_workers_find(subid, true);
+			workers = logicalrep_workers_find(subid, true, false);
 			foreach(lc2, workers)
 			{
 				LogicalRepWorker *worker = (LogicalRepWorker *) lfirst(lc2);
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index baf9b89dc4..2ad6dca993 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -804,8 +804,10 @@ ReplicationSlotDrop(const char *name, bool nowait)
  * Change the definition of the slot identified by the specified name.
  */
 void
-ReplicationSlotAlter(const char *name, bool failover)
+ReplicationSlotAlter(const char *name, bool failover, bool two_phase)
 {
+	bool		update_slot = false;
+
 	Assert(MyReplicationSlot == NULL);
 
 	ReplicationSlotAcquire(name, false);
@@ -854,6 +856,20 @@ ReplicationSlotAlter(const char *name, bool failover)
 		MyReplicationSlot->data.failover = failover;
 		SpinLockRelease(&MyReplicationSlot->mutex);
 
+		update_slot = true;
+	}
+
+	if (MyReplicationSlot->data.two_phase != two_phase)
+	{
+		SpinLockAcquire(&MyReplicationSlot->mutex);
+		MyReplicationSlot->data.two_phase = two_phase;
+		SpinLockRelease(&MyReplicationSlot->mutex);
+
+		update_slot = true;
+	}
+
+	if (update_slot)
+	{
 		ReplicationSlotMarkDirty();
 		ReplicationSlotSave();
 	}
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 754f505c13..af776fccb8 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1409,9 +1409,11 @@ DropReplicationSlot(DropReplicationSlotCmd *cmd)
  * Process extra options given to ALTER_REPLICATION_SLOT.
  */
 static void
-ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd, bool *failover)
+ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd,
+						  bool *failover, bool *two_phase)
 {
 	bool		failover_given = false;
+	bool		two_phase_given = false;
 
 	/* Parse options */
 	foreach_ptr(DefElem, defel, cmd->options)
@@ -1425,6 +1427,15 @@ ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd, bool *failover)
 			failover_given = true;
 			*failover = defGetBoolean(defel);
 		}
+		else if (strcmp(defel->defname, "two_phase") == 0)
+		{
+			if (two_phase_given)
+				ereport(ERROR,
+						(errcode(ERRCODE_SYNTAX_ERROR),
+						 errmsg("conflicting or redundant options")));
+			two_phase_given = true;
+			*two_phase = defGetBoolean(defel);
+		}
 		else
 			elog(ERROR, "unrecognized option: %s", defel->defname);
 	}
@@ -1437,9 +1448,10 @@ static void
 AlterReplicationSlot(AlterReplicationSlotCmd *cmd)
 {
 	bool		failover = false;
+	bool		two_phase = false;
 
-	ParseAlterReplSlotOptions(cmd, &failover);
-	ReplicationSlotAlter(cmd->slotname, failover);
+	ParseAlterReplSlotOptions(cmd, &failover, &two_phase);
+	ReplicationSlotAlter(cmd->slotname, failover, two_phase);
 }
 
 /*
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
index d453e224d9..891face1b6 100644
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -1948,7 +1948,7 @@ psql_completion(const char *text, int start, int end)
 	else if (HeadMatches("ALTER", "SUBSCRIPTION", MatchAny) && TailMatches("SET", "("))
 		COMPLETE_WITH("binary", "disable_on_error", "failover", "origin",
 					  "password_required", "run_as_owner", "slot_name",
-					  "streaming", "synchronous_commit");
+					  "streaming", "synchronous_commit", "two_phase");
 	/* ALTER SUBSCRIPTION <name> SKIP ( */
 	else if (HeadMatches("ALTER", "SUBSCRIPTION", MatchAny) && TailMatches("SKIP", "("))
 		COMPLETE_WITH("lsn");
diff --git a/src/include/access/twophase.h b/src/include/access/twophase.h
index 56248c0006..d37e06fdee 100644
--- a/src/include/access/twophase.h
+++ b/src/include/access/twophase.h
@@ -62,4 +62,9 @@ extern void PrepareRedoRemove(TransactionId xid, bool giveWarning);
 extern void restoreTwoPhaseData(void);
 extern bool LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 						TimestampTz origin_prepare_timestamp);
+
+extern void TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid,
+								   int szgid);
+extern bool LookupGXactBySubid(Oid subid);
+
 #endif							/* TWOPHASE_H */
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index c9675ee87c..163a4a911a 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -243,7 +243,8 @@ extern void ReplicationSlotCreate(const char *name, bool db_specific,
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
 extern void ReplicationSlotDropAcquired(void);
-extern void ReplicationSlotAlter(const char *name, bool failover);
+extern void ReplicationSlotAlter(const char *name, bool failover,
+								 bool two_phase);
 
 extern void ReplicationSlotAcquire(const char *name, bool nowait);
 extern void ReplicationSlotRelease(void);
diff --git a/src/include/replication/walreceiver.h b/src/include/replication/walreceiver.h
index 12f71fa99b..31fa1257ec 100644
--- a/src/include/replication/walreceiver.h
+++ b/src/include/replication/walreceiver.h
@@ -372,12 +372,13 @@ typedef char *(*walrcv_create_slot_fn) (WalReceiverConn *conn,
 /*
  * walrcv_alter_slot_fn
  *
- * Change the definition of a replication slot. Currently, it only supports
- * changing the failover property of the slot.
+ * Change the definition of a replication slot. Currently, it supports
+ * changing the failover and the two_phase property of the slot.
  */
 typedef void (*walrcv_alter_slot_fn) (WalReceiverConn *conn,
 									  const char *slotname,
-									  bool failover);
+									  bool failover,
+									  bool two_phase);
 
 /*
  * walrcv_get_backend_pid_fn
@@ -455,8 +456,8 @@ extern PGDLLIMPORT WalReceiverFunctionsType *WalReceiverFunctions;
 	WalReceiverFunctions->walrcv_send(conn, buffer, nbytes)
 #define walrcv_create_slot(conn, slotname, temporary, two_phase, failover, snapshot_action, lsn) \
 	WalReceiverFunctions->walrcv_create_slot(conn, slotname, temporary, two_phase, failover, snapshot_action, lsn)
-#define walrcv_alter_slot(conn, slotname, failover) \
-	WalReceiverFunctions->walrcv_alter_slot(conn, slotname, failover)
+#define walrcv_alter_slot(conn, slotname, failover, two_phase) \
+	WalReceiverFunctions->walrcv_alter_slot(conn, slotname, failover, two_phase)
 #define walrcv_get_backend_pid(conn) \
 	WalReceiverFunctions->walrcv_get_backend_pid(conn)
 #define walrcv_exec(conn, exec, nRetTypes, retTypes) \
diff --git a/src/include/replication/worker_internal.h b/src/include/replication/worker_internal.h
index 515aefd519..990f5242f9 100644
--- a/src/include/replication/worker_internal.h
+++ b/src/include/replication/worker_internal.h
@@ -240,7 +240,8 @@ extern PGDLLIMPORT bool InitializingApplyWorker;
 extern void logicalrep_worker_attach(int slot);
 extern LogicalRepWorker *logicalrep_worker_find(Oid subid, Oid relid,
 												bool only_running);
-extern List *logicalrep_workers_find(Oid subid, bool only_running);
+extern List *logicalrep_workers_find(Oid subid, bool only_running,
+									 bool require_lock);
 extern bool logicalrep_worker_launch(LogicalRepWorkerType wtype,
 									 Oid dbid, Oid subid, const char *subname,
 									 Oid userid, Oid relid,
diff --git a/src/test/regress/expected/subscription.out b/src/test/regress/expected/subscription.out
index 0f2a25cdc1..51fa4b9690 100644
--- a/src/test/regress/expected/subscription.out
+++ b/src/test/regress/expected/subscription.out
@@ -377,10 +377,7 @@ HINT:  To initiate replication, you must manually create the replication slot, e
  regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | p                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
---fail - alter of two_phase option not supported.
-ALTER SUBSCRIPTION regress_testsub SET (two_phase = false);
-ERROR:  unrecognized subscription parameter: "two_phase"
--- but can alter streaming when two_phase enabled
+-- We can alter streaming when two_phase enabled
 ALTER SUBSCRIPTION regress_testsub SET (streaming = true);
 \dRs+
                                                                                                                 List of subscriptions
diff --git a/src/test/regress/sql/subscription.sql b/src/test/regress/sql/subscription.sql
index 3e5ba4cb8c..a3886d79ca 100644
--- a/src/test/regress/sql/subscription.sql
+++ b/src/test/regress/sql/subscription.sql
@@ -256,10 +256,7 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUBLICATION testpub WITH (connect = false, two_phase = true);
 
 \dRs+
---fail - alter of two_phase option not supported.
-ALTER SUBSCRIPTION regress_testsub SET (two_phase = false);
-
--- but can alter streaming when two_phase enabled
+-- We can alter streaming when two_phase enabled
 ALTER SUBSCRIPTION regress_testsub SET (streaming = true);
 
 \dRs+
diff --git a/src/test/subscription/t/021_twophase.pl b/src/test/subscription/t/021_twophase.pl
index 9437cd4c3b..4e8f627f7b 100644
--- a/src/test/subscription/t/021_twophase.pl
+++ b/src/test/subscription/t/021_twophase.pl
@@ -367,6 +367,81 @@ $result =
   $node_subscriber->safe_psql('postgres', "SELECT count(*) FROM tab_copy;");
 is($result, qq(2), 'replicated data in subscriber table');
 
+# Clean up
+$node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub");
+
+###############################
+# Disable the subscription and alter it to two_phase = false,
+# then verify that the altered subscription reflects the two_phase option.
+###############################
+
+# Alter subscription two_phase to false
+$node_subscriber->safe_psql('postgres',
+    "ALTER SUBSCRIPTION tap_sub_copy DISABLE;");
+$node_subscriber->poll_query_until('postgres',
+    "SELECT count(*) = 0 FROM pg_stat_activity WHERE backend_type = 'logical replication worker'"
+);
+$node_subscriber->safe_psql(
+	'postgres', "
+    ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = false);
+    ALTER SUBSCRIPTION tap_sub_copy ENABLE;");
+
+# Wait for subscription startup
+$node_subscriber->wait_for_subscription_sync($node_publisher, $appname_copy);
+
+# Make sure that the two-phase is disabled on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT subtwophasestate FROM pg_subscription WHERE subname = 'tap_sub_copy';"
+);
+is($result, qq(d), 'two-phase should be disabled');
+
+# Now do a prepare on the publisher and make sure that it is not replicated.
+$node_publisher->safe_psql(
+	'postgres', qq{
+    BEGIN;
+    INSERT INTO tab_copy VALUES (100);
+    PREPARE TRANSACTION 'newgid';
+	});
+
+# Wait for the subscriber to catchup
+$node_publisher->wait_for_catchup($appname_copy);
+
+# Make sure there are no prepared transactions on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT count(*) FROM pg_prepared_xacts;");
+is($result, qq(0), 'should be no prepared transactions on subscriber');
+
+# Now commit the insert and verify that it is replicated
+$node_publisher->safe_psql('postgres', "COMMIT PREPARED 'newgid';");
+
+# Wait for the subscriber to catchup
+$node_publisher->wait_for_catchup($appname_copy);
+
+# Make sure that the committed transaction is replicated.
+$result =
+  $node_subscriber->safe_psql('postgres', "SELECT count(*) FROM tab_copy;");
+is($result, qq(3), 'replicated data in subscriber table');
+
+# Alter subscription two_phase to true
+$node_subscriber->safe_psql('postgres',
+    "ALTER SUBSCRIPTION tap_sub_copy DISABLE;");
+$node_subscriber->poll_query_until('postgres',
+    "SELECT count(*) = 0 FROM pg_stat_activity WHERE backend_type = 'logical replication worker'"
+);
+$node_subscriber->safe_psql(
+	'postgres', "
+    ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = true);
+    ALTER SUBSCRIPTION tap_sub_copy ENABLE;");
+
+# Wait for subscription startup
+$node_subscriber->wait_for_subscription_sync($node_publisher, $appname_copy);
+
+# Make sure that the two-phase is enabled on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT subtwophasestate FROM pg_subscription WHERE subname = 'tap_sub_copy';"
+);
+is($result, qq(e), 'two-phase should be enabled');
+
 $node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub_copy;");
 $node_publisher->safe_psql('postgres', "DROP PUBLICATION tap_pub_copy;");
 
@@ -374,8 +449,6 @@ $node_publisher->safe_psql('postgres', "DROP PUBLICATION tap_pub_copy;");
 # check all the cleanup
 ###############################
 
-$node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub");
-
 $result = $node_subscriber->safe_psql('postgres',
 	"SELECT count(*) FROM pg_subscription");
 is($result, qq(0), 'check subscription was dropped on subscriber');
-- 
2.43.0

From f7bc80a31082e1744793ef23cbe990a9d8243d07 Mon Sep 17 00:00:00 2001
From: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Date: Wed, 17 Apr 2024 06:18:23 +0000
Subject: [PATCH v15 2/4] Alter slot option two_phase only when altering "true"
 to "false"
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Since the two_phase option is controlled by both the publisher (as a slot option)
and the subscriber (as a subscription option), the slot option must also be
modified.

Regarding the false->true case, the backend process alters the subtwophase to
LOGICALREP_TWOPHASE_STATE_PENDING once. After the subscription is enabled, a new
logical replication worker requests to change the two_phase option of its slot
from pending to true after the initial data synchronization is done. The code
path is the same as the case in which two_phase is initially set to true, so
there is no need to do something remarkable. However, for the true->false case,
the backend must connect to the publisher and expressly change the parameter
because the apply worker does not alter the option to false. Because this
operation cannot be rolled back, altering the two_phase parameter from "true"
to "false" within a transaction is prohibited.
---
 doc/src/sgml/ref/alter_subscription.sgml      |  2 +-
 src/backend/commands/subscriptioncmds.c       | 43 ++++++++++++++++---
 .../libpqwalreceiver/libpqwalreceiver.c       | 23 +++++++---
 src/include/replication/walreceiver.h         |  5 ++-
 src/test/subscription/t/021_twophase.pl       | 41 +++++++++++-------
 5 files changed, 83 insertions(+), 31 deletions(-)

diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index 0b23df1b77..475a42a2e3 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -70,7 +70,7 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
    <command>ALTER SUBSCRIPTION ... {SET|ADD|DROP} PUBLICATION ...</command>
    with <literal>refresh</literal> option as <literal>true</literal>,
    <command>ALTER SUBSCRIPTION ... SET (failover = true|false)</command> and
-   <command>ALTER SUBSCRIPTION ... SET (two_phase = true|false)</command>
+   <command>ALTER SUBSCRIPTION ... SET (two_phase = off)</command>
    cannot be executed inside a transaction block.
 
    These commands also cannot be executed when the subscription has
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index 1d57f12942..67b1dc30a5 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -1085,6 +1085,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 	Form_pg_subscription form;
 	bits32		supported_opts;
 	SubOpts		opts = {0};
+	bool		update_failover;
+	bool		update_two_phase;
 
 	rel = table_open(SubscriptionRelationId, RowExclusiveLock);
 
@@ -1181,10 +1183,25 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 								 errhint("Resolve these transactions and try again")));
 
 					/*
-					 * The changed two_phase option of the slot can't be
-					 * rolled back.
+					 * Altering the parameter from "true" to "false" within a
+					 * transaction is prohibited. Since the apply worker does
+					 * not alter the slot option to false, the backend must
+					 * connect to the publisher and expressly change the
+					 * parameter.
+					 *
+					 * There is no need to do something remarkable regarding
+					 * the "false" to "true" case; the backend process alters
+					 * subtwophase to LOGICALREP_TWOPHASE_STATE_PENDING once.
+					 * After the subscription is enabled, a new logical
+					 * replication worker requests to change the two_phase
+					 * option of its slot from pending to true when the
+					 * initial data synchronization is done. The code path is
+					 * the same as the case in which two_phase is initially
+					 * set to true.
 					 */
-					PreventInTransactionBlock(isTopLevel, "ALTER SUBSCRIPTION ... SET (two_phase)");
+					if (!opts.twophase)
+						PreventInTransactionBlock(isTopLevel,
+												  "ALTER SUBSCRIPTION ... SET (two_phase = false)");
 
 					/* Change system catalog acoordingly */
 					values[Anum_pg_subscription_subtwophasestate - 1] =
@@ -1542,14 +1559,24 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 	}
 
 	/*
-	 * Try to acquire the connection necessary for altering slot.
+	 * Check the need to alter the replication slot. Failover and two_phase
+	 * options are controlled by both the publisher (as a slot option) and the
+	 * subscriber (as a subscription option). The slot option must be altered
+	 * only when changing "true" to "false". The reason has already been
+	 * described in the ALTER_SUBSCRIPTION_OPTIONS section of this function.
+	 */
+	update_failover = replaces[Anum_pg_subscription_subfailover - 1];
+	update_two_phase = (replaces[Anum_pg_subscription_subtwophasestate - 1] &&
+						!opts.twophase);
+
+	/*
+	 * Try to acquire the connection necessary for altering slot, if needed.
 	 *
 	 * This has to be at the end because otherwise if there is an error while
 	 * doing the database operations we won't be able to rollback altered
 	 * slot.
 	 */
-	if (replaces[Anum_pg_subscription_subfailover - 1] ||
-		replaces[Anum_pg_subscription_subtwophasestate - 1])
+	if (update_failover || update_two_phase)
 	{
 		bool		must_use_password;
 		char	   *err;
@@ -1569,7 +1596,9 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 
 		PG_TRY();
 		{
-			walrcv_alter_slot(wrconn, sub->slotname, opts.failover, opts.twophase);
+			walrcv_alter_slot(wrconn, sub->slotname,
+							  update_failover ? &opts.failover : NULL,
+							  update_two_phase ? &opts.twophase : NULL);
 		}
 		PG_FINALLY();
 		{
diff --git a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
index 2f035a0c3c..07dfec947d 100644
--- a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
+++ b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
@@ -80,7 +80,7 @@ static char *libpqrcv_create_slot(WalReceiverConn *conn,
 								  CRSSnapshotAction snapshot_action,
 								  XLogRecPtr *lsn);
 static void libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-								bool failover, bool two_phase);
+								const bool *failover, const bool *two_phase);
 static pid_t libpqrcv_get_backend_pid(WalReceiverConn *conn);
 static WalRcvExecResult *libpqrcv_exec(WalReceiverConn *conn,
 									   const char *query,
@@ -1121,16 +1121,27 @@ libpqrcv_create_slot(WalReceiverConn *conn, const char *slotname,
  */
 static void
 libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-					bool failover, bool two_phase)
+					const bool *failover, const bool *two_phase)
 {
 	StringInfoData cmd;
 	PGresult   *res;
 
 	initStringInfo(&cmd);
-	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( FAILOVER %s, TWO_PHASE %s )",
-					 quote_identifier(slotname),
-					 failover ? "true" : "false",
-					 two_phase ? "true" : "false");
+	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( ",
+					 quote_identifier(slotname));
+
+	if (failover)
+		appendStringInfo(&cmd, "FAILOVER %s",
+						 *failover ? "true" : "false");
+
+	if (failover && two_phase)
+		appendStringInfo(&cmd, ", ");
+
+	if (two_phase)
+		appendStringInfo(&cmd, "TWO_PHASE %s",
+						 *two_phase ? "true" : "false");
+
+	appendStringInfoString(&cmd, " );");
 
 	res = libpqrcv_PQexec(conn->streamConn, cmd.data);
 	pfree(cmd.data);
diff --git a/src/include/replication/walreceiver.h b/src/include/replication/walreceiver.h
index 31fa1257ec..7ffa5a58b3 100644
--- a/src/include/replication/walreceiver.h
+++ b/src/include/replication/walreceiver.h
@@ -377,8 +377,9 @@ typedef char *(*walrcv_create_slot_fn) (WalReceiverConn *conn,
  */
 typedef void (*walrcv_alter_slot_fn) (WalReceiverConn *conn,
 									  const char *slotname,
-									  bool failover,
-									  bool two_phase);
+									  const bool *failover,
+									  const bool *two_phase);
+
 
 /*
  * walrcv_get_backend_pid_fn
diff --git a/src/test/subscription/t/021_twophase.pl b/src/test/subscription/t/021_twophase.pl
index 4e8f627f7b..f56dff4b12 100644
--- a/src/test/subscription/t/021_twophase.pl
+++ b/src/test/subscription/t/021_twophase.pl
@@ -375,6 +375,12 @@ $node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub");
 # then verify that the altered subscription reflects the two_phase option.
 ###############################
 
+# Confirm two-phase slot option is enabled before altering
+$result = $node_publisher->safe_psql('postgres',
+	"SELECT two_phase FROM pg_replication_slots WHERE slot_name = 'tap_sub_copy';"
+);
+is($result, qq(t), 'two-phase is enabled');
+
 # Alter subscription two_phase to false
 $node_subscriber->safe_psql('postgres',
     "ALTER SUBSCRIPTION tap_sub_copy DISABLE;");
@@ -393,7 +399,13 @@ $node_subscriber->wait_for_subscription_sync($node_publisher, $appname_copy);
 $result = $node_subscriber->safe_psql('postgres',
 	"SELECT subtwophasestate FROM pg_subscription WHERE subname = 'tap_sub_copy';"
 );
-is($result, qq(d), 'two-phase should be disabled');
+is($result, qq(d), 'two-phase subscription option should be disabled');
+
+# Make sure that the two-phase slot option is also disabled
+$result = $node_publisher->safe_psql('postgres',
+	"SELECT two_phase FROM pg_replication_slots WHERE slot_name = 'tap_sub_copy';"
+);
+is($result, qq(f), 'two-phase slot option should be disabled');
 
 # Now do a prepare on the publisher and make sure that it is not replicated.
 $node_publisher->safe_psql(
@@ -411,6 +423,19 @@ $result = $node_subscriber->safe_psql('postgres',
 	"SELECT count(*) FROM pg_prepared_xacts;");
 is($result, qq(0), 'should be no prepared transactions on subscriber');
 
+# Toggle the two_phase to "true" *before* the COMMIT PREPARED. Since we are the
+# special path for the case where both two_phase and failover are altered, it
+# is also set to "true".
+$node_subscriber->safe_psql('postgres',
+    "ALTER SUBSCRIPTION tap_sub_copy DISABLE;");
+$node_subscriber->poll_query_until('postgres',
+    "SELECT count(*) = 0 FROM pg_stat_activity WHERE backend_type = 'logical replication worker'"
+);
+$node_subscriber->safe_psql(
+	'postgres', "
+    ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = true, failover = true);
+    ALTER SUBSCRIPTION tap_sub_copy ENABLE;");
+
 # Now commit the insert and verify that it is replicated
 $node_publisher->safe_psql('postgres', "COMMIT PREPARED 'newgid';");
 
@@ -422,20 +447,6 @@ $result =
   $node_subscriber->safe_psql('postgres', "SELECT count(*) FROM tab_copy;");
 is($result, qq(3), 'replicated data in subscriber table');
 
-# Alter subscription two_phase to true
-$node_subscriber->safe_psql('postgres',
-    "ALTER SUBSCRIPTION tap_sub_copy DISABLE;");
-$node_subscriber->poll_query_until('postgres',
-    "SELECT count(*) = 0 FROM pg_stat_activity WHERE backend_type = 'logical replication worker'"
-);
-$node_subscriber->safe_psql(
-	'postgres', "
-    ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = true);
-    ALTER SUBSCRIPTION tap_sub_copy ENABLE;");
-
-# Wait for subscription startup
-$node_subscriber->wait_for_subscription_sync($node_publisher, $appname_copy);
-
 # Make sure that the two-phase is enabled on the subscriber
 $result = $node_subscriber->safe_psql('postgres',
 	"SELECT subtwophasestate FROM pg_subscription WHERE subname = 'tap_sub_copy';"
-- 
2.43.0

From 1e7d3742095f9869916ee71f26211bb585461856 Mon Sep 17 00:00:00 2001
From: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Date: Mon, 8 Apr 2024 12:39:12 +0000
Subject: [PATCH v15 3/4] Abort prepared transactions while altering two_phase
 to off

If we alter the two_phase parameter from "on" to "off" and there are prepared
transactions on the subscriber, they won't be resolved. To avoid this issue, we
allow the backend to abort all prepared transactions while altering the
subscription.
---
 doc/src/sgml/ref/alter_subscription.sgml | 11 +++-
 src/backend/access/transam/twophase.c    | 17 +++---
 src/backend/commands/subscriptioncmds.c  | 75 +++++++++++++++---------
 src/include/access/twophase.h            |  3 +-
 src/test/subscription/t/021_twophase.pl  | 53 +++++++++++++++--
 5 files changed, 115 insertions(+), 44 deletions(-)

diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index 475a42a2e3..8801f37f0e 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -233,8 +233,6 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>, and
       <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>.
       Only a superuser can set <literal>password_required = false</literal>.
-      The <literal>two_phase</literal> parameter can only be altered when the
-      subscription is disabled.
      </para>
 
      <para>
@@ -256,6 +254,15 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>
       option is enabled.
      </para>
+
+     <para>
+      The <literal>two_phase</literal> parameter can only be altered when the
+      subscription is disabled. When altering the parameter from <literal>true</literal>
+      to <literal>false</literal>, the backend process checks for any incomplete
+      prepared transactions done by the logical replication worker (from when
+      <literal>two_phase</literal> parameter was still <literal>true</literal>)
+      and, if any are found, those are aborted.
+     </para>
     </listitem>
    </varlistentry>
 
diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index 35bce6809d..0be8a15367 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -2719,13 +2719,13 @@ IsTwoPhaseTransactionGidForSubid(Oid subid, char *gid)
 }
 
 /*
- * LookupGXactBySubid
- *		Check if the prepared transaction done by apply worker exists.
+ * GetGidListBySubid
+ *      Get a list of GIDs which is PREPARE'd by the given subscription.
  */
-bool
-LookupGXactBySubid(Oid subid)
+List *
+GetGidListBySubid(Oid subid)
 {
-	bool		found = false;
+	List	   *list = NIL;
 
 	LWLockAcquire(TwoPhaseStateLock, LW_SHARED);
 	for (int i = 0; i < TwoPhaseState->numPrepXacts; i++)
@@ -2735,11 +2735,8 @@ LookupGXactBySubid(Oid subid)
 		/* Ignore not-yet-valid GIDs. */
 		if (gxact->valid &&
 			IsTwoPhaseTransactionGidForSubid(subid, gxact->gid))
-		{
-			found = true;
-			break;
-		}
+			list = lappend(list, pstrdup(gxact->gid));
 	}
 	LWLockRelease(TwoPhaseStateLock);
-	return found;
+	return list;
 }
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index 67b1dc30a5..401ea1dc88 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -1171,38 +1171,59 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 								 errhint("Wait certain time and try again.")));
 
 					/*
-					 * two_phase cannot be disabled if there are any
-					 * uncommitted prepared transactions present.
-					 */
-					if (!opts.twophase &&
-						form->subtwophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
-						LookupGXactBySubid(subid))
-						ereport(ERROR,
-								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-								 errmsg("cannot disable two_phase when uncommitted prepared transactions present"),
-								 errhint("Resolve these transactions and try again")));
-
-					/*
-					 * Altering the parameter from "true" to "false" within a
-					 * transaction is prohibited. Since the apply worker does
-					 * not alter the slot option to false, the backend must
-					 * connect to the publisher and expressly change the
-					 * parameter.
-					 *
-					 * There is no need to do something remarkable regarding
-					 * the "false" to "true" case; the backend process alters
-					 * subtwophase to LOGICALREP_TWOPHASE_STATE_PENDING once.
-					 * After the subscription is enabled, a new logical
-					 * replication worker requests to change the two_phase
-					 * option of its slot from pending to true when the
-					 * initial data synchronization is done. The code path is
-					 * the same as the case in which two_phase is initially
-					 * set to true.
+					 * If two_phase was previously enabled, there is a
+					 * possibility that transactions have already been
+					 * PREPARE'd. They must be checked and rolled back.
 					 */
 					if (!opts.twophase)
+					{
+						List	   *prepared_xacts;
+
+						/*
+						 * Altering the parameter from "true" to "false"
+						 * within a transaction is prohibited. Since the apply
+						 * worker does not alter the slot option to false, the
+						 * backend must connect to the publisher and expressly
+						 * change the parameter.
+						 *
+						 * There is no need to do something remarkable
+						 * regarding the "false" to "true" case; the backend
+						 * process alters subtwophase to
+						 * LOGICALREP_TWOPHASE_STATE_PENDING once. After the
+						 * subscription is enabled, a new logical replication
+						 * worker requests to change the two_phase option of
+						 * its slot from pending to true when the initial data
+						 * synchronization is done. The code path is the same
+						 * as the case in which two_phase is initially set to
+						 * true.
+						 */
 						PreventInTransactionBlock(isTopLevel,
 												  "ALTER SUBSCRIPTION ... SET (two_phase = false)");
 
+						/*
+						 * To prevent prepared transactions from being
+						 * isolated, they must manually be aborted.
+						 */
+						if (sub->twophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
+							(prepared_xacts = GetGidListBySubid(subid)) != NIL)
+						{
+							ereport(NOTICE,
+									(errmsg_plural("requested altering to %s but there is prepared transaction done by the subscription",
+												   "requested altering to %s but there are prepared transactions done by the subscription",
+												   list_length(prepared_xacts),
+												   "two_phase = false"),
+									 errdetail_plural("Such a transaction is being rollbacked.",
+													  "Such transactions are being rollbacked.",
+													  list_length(prepared_xacts))));
+
+							/* Abort all listed transactions */
+							foreach_ptr(char, gid, prepared_xacts)
+								FinishPreparedTransaction(gid, false);
+
+							list_free_deep(prepared_xacts);
+						}
+					}
+
 					/* Change system catalog acoordingly */
 					values[Anum_pg_subscription_subtwophasestate - 1] =
 						CharGetDatum(opts.twophase ?
diff --git a/src/include/access/twophase.h b/src/include/access/twophase.h
index d37e06fdee..f7a5cf0c12 100644
--- a/src/include/access/twophase.h
+++ b/src/include/access/twophase.h
@@ -18,6 +18,7 @@
 #include "access/xlogdefs.h"
 #include "datatype/timestamp.h"
 #include "storage/lock.h"
+#include "nodes/pg_list.h"
 
 /*
  * GlobalTransactionData is defined in twophase.c; other places have no
@@ -65,6 +66,6 @@ extern bool LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 
 extern void TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid,
 								   int szgid);
-extern bool LookupGXactBySubid(Oid subid);
+extern List *GetGidListBySubid(Oid subid);
 
 #endif							/* TWOPHASE_H */
diff --git a/src/test/subscription/t/021_twophase.pl b/src/test/subscription/t/021_twophase.pl
index f56dff4b12..c3e15e537b 100644
--- a/src/test/subscription/t/021_twophase.pl
+++ b/src/test/subscription/t/021_twophase.pl
@@ -383,9 +383,9 @@ is($result, qq(t), 'two-phase is enabled');
 
 # Alter subscription two_phase to false
 $node_subscriber->safe_psql('postgres',
-    "ALTER SUBSCRIPTION tap_sub_copy DISABLE;");
+	"ALTER SUBSCRIPTION tap_sub_copy DISABLE;");
 $node_subscriber->poll_query_until('postgres',
-    "SELECT count(*) = 0 FROM pg_stat_activity WHERE backend_type = 'logical replication worker'"
+	"SELECT count(*) = 0 FROM pg_stat_activity WHERE backend_type = 'logical replication worker'"
 );
 $node_subscriber->safe_psql(
 	'postgres', "
@@ -427,9 +427,9 @@ is($result, qq(0), 'should be no prepared transactions on subscriber');
 # special path for the case where both two_phase and failover are altered, it
 # is also set to "true".
 $node_subscriber->safe_psql('postgres',
-    "ALTER SUBSCRIPTION tap_sub_copy DISABLE;");
+	"ALTER SUBSCRIPTION tap_sub_copy DISABLE;");
 $node_subscriber->poll_query_until('postgres',
-    "SELECT count(*) = 0 FROM pg_stat_activity WHERE backend_type = 'logical replication worker'"
+	"SELECT count(*) = 0 FROM pg_stat_activity WHERE backend_type = 'logical replication worker'"
 );
 $node_subscriber->safe_psql(
 	'postgres', "
@@ -453,6 +453,51 @@ $result = $node_subscriber->safe_psql('postgres',
 );
 is($result, qq(e), 'two-phase should be enabled');
 
+#####################
+# Check the case that prepared transactions exist on the subscriber node
+#####################
+
+# Prepare a transaction to insert some tuples into the table
+$node_publisher->safe_psql(
+	'postgres', "
+	BEGIN;
+	INSERT INTO tab_copy VALUES (101);
+	PREPARE TRANSACTION 'newgid';");
+
+$node_publisher->wait_for_catchup($appname_copy);
+
+# Verify the prepared transaction has been replicated to the subscriber because
+# two_phase is set to "true".
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT count(*) FROM pg_prepared_xacts;");
+is($result, q(1), "transaction has been prepared on subscriber");
+
+# Toggle the two_phase to "false" before the COMMIT PREPARED
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy DISABLE;");
+$node_subscriber->poll_query_until('postgres',
+	"SELECT count(*) = 0 FROM pg_stat_activity WHERE backend_type = 'logical replication worker'"
+);
+$node_subscriber->safe_psql(
+	'postgres', "
+    ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = false);
+    ALTER SUBSCRIPTION tap_sub_copy ENABLE;");
+
+# Verify any prepared transactions are aborted because two_phase is changed to
+# "false".
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT count(*) FROM pg_prepared_xacts;");
+is($result, q(0), "prepared transaction done by worker is aborted");
+
+# Do COMMIT PREPARED the prepared transaction
+$node_publisher->safe_psql('postgres', "COMMIT PREPARED 'newgid';");
+$node_publisher->wait_for_catchup($appname_copy);
+
+# Verify inserted tuples are replicated
+$result =
+  $node_subscriber->safe_psql('postgres', "SELECT count(*) FROM tab_copy;");
+is($result, q(4), "prepared transactions on publisher can be replicated");
+
 $node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub_copy;");
 $node_publisher->safe_psql('postgres', "DROP PUBLICATION tap_pub_copy;");
 
-- 
2.43.0

From b2e8dd01fb66798ef61638b4f7e99da1278f2f92 Mon Sep 17 00:00:00 2001
From: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Date: Fri, 19 Apr 2024 11:03:19 +0000
Subject: [PATCH v15 4/4] Add force_alter option for ALTER SUBSCRIPTION ... SET
 command

Previously, all prepared transactions on the standby were rolled back when
toggling two_phase from "true" to "false". However, this operation may not be
expected by users. To ensure users understand what happens, we added the
"force_alter" parameter. When two_phase is toggling to "false", and there are
prepared transactions, they will be aborted only when "force_alter" is set to
true. Otherwise, an ERROR occurs.
---
 doc/src/sgml/catalogs.sgml                 |  12 ++
 doc/src/sgml/ref/alter_subscription.sgml   |  16 ++-
 doc/src/sgml/ref/create_subscription.sgml  |  24 ++++
 src/backend/catalog/pg_subscription.c      |   1 +
 src/backend/catalog/system_views.sql       |   2 +-
 src/backend/commands/subscriptioncmds.c    |  36 ++++-
 src/bin/pg_dump/pg_dump.c                  |  18 ++-
 src/bin/pg_dump/pg_dump.h                  |   1 +
 src/bin/psql/describe.c                    |   7 +-
 src/include/catalog/pg_subscription.h      |  13 ++
 src/test/regress/expected/subscription.out | 152 ++++++++++-----------
 src/test/subscription/t/021_twophase.pl    |  25 +++-
 12 files changed, 216 insertions(+), 91 deletions(-)

diff --git a/doc/src/sgml/catalogs.sgml b/doc/src/sgml/catalogs.sgml
index b654fae1b2..bca2f0c77a 100644
--- a/doc/src/sgml/catalogs.sgml
+++ b/doc/src/sgml/catalogs.sgml
@@ -8035,6 +8035,18 @@ SCRAM-SHA-256$<replaceable>&lt;iteration count&gt;</replaceable>:<replaceable>&l
       </para></entry>
      </row>
 
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>subforcealter</structfield> <type>bool</type>
+      </para>
+      <para>
+       If true, then the <link linkend="sql-altersubscription"><command>ALTER SUBSCRIPTION</command></link>
+       can sometimes be forced to proceed instead of giving an error. See
+       <link linkend="sql-createsubscription-params-with-force-alter"><literal>force_alter</literal></link>
+       parameter for details about when this might be useful.
+      </para></entry>
+     </row>
+
      <row>
       <entry role="catalog_table_entry"><para role="column_definition">
        <structfield>subconninfo</structfield> <type>text</type>
diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index 8801f37f0e..ab2cdaeaa3 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -230,8 +230,9 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-password-required"><literal>password_required</literal></link>,
       <link linkend="sql-createsubscription-params-with-run-as-owner"><literal>run_as_owner</literal></link>,
       <link linkend="sql-createsubscription-params-with-origin"><literal>origin</literal></link>,
-      <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>, and
-      <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>.
+      <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>,
+      <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>, and
+      <link linkend="sql-createsubscription-params-with-force-alter"><literal>force_alter</literal></link>
       Only a superuser can set <literal>password_required = false</literal>.
      </para>
 
@@ -257,11 +258,12 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
 
      <para>
       The <literal>two_phase</literal> parameter can only be altered when the
-      subscription is disabled. When altering the parameter from <literal>true</literal>
-      to <literal>false</literal>, the backend process checks for any incomplete
-      prepared transactions done by the logical replication worker (from when
-      <literal>two_phase</literal> parameter was still <literal>true</literal>)
-      and, if any are found, those are aborted.
+      subscription is disabled. Altering the parameter from <literal>true</literal>
+      to <literal>false</literal> will give an error when there are prepared
+      transactions done by the logical replication worker. If you want to alter
+      the parameter forcibly in this case,
+      <link linkend="sql-createsubscription-params-with-force-alter"><literal>force_alter</literal></link>
+      option must be set to <literal>true</literal>.
      </para>
     </listitem>
    </varlistentry>
diff --git a/doc/src/sgml/ref/create_subscription.sgml b/doc/src/sgml/ref/create_subscription.sgml
index 740b7d9421..83ac52f865 100644
--- a/doc/src/sgml/ref/create_subscription.sgml
+++ b/doc/src/sgml/ref/create_subscription.sgml
@@ -428,6 +428,30 @@ CREATE SUBSCRIPTION <replaceable class="parameter">subscription_name</replaceabl
          </para>
         </listitem>
        </varlistentry>
+
+       <varlistentry id="sql-createsubscription-params-with-force-alter">
+        <term><literal>force_alter</literal> (<type>boolean</type>)</term>
+        <listitem>
+         <para>
+          Specifies if the <link linkend="sql-altersubscription"><command>ALTER SUBSCRIPTION</command></link>
+          can be forced to proceed instead of giving an error.
+         </para>
+         <para>
+          There is currently only one scenario where this parameter has any
+          effect: When altering <literal>two_phase</literal> option from
+          <literal>true</literal> to <literal>false</literal> it is possible
+          for there to be incomplete prepared transactions done by the logical
+          replication worker (from when <literal>two_phase</literal> parameter
+          was still <literal>true</literal>). If <literal>force_alter</literal>
+          is <literal>false</literal>, then this will give an error; if
+          <literal>force_alter</literal> is <literal>true</literal>, then the
+          incomplete prepared transactions are aborted and the alter will proceed.
+         </para>
+         <para>
+          The default is <literal>false</literal>.
+         </para>
+        </listitem>
+       </varlistentry>
       </variablelist></para>
 
     </listitem>
diff --git a/src/backend/catalog/pg_subscription.c b/src/backend/catalog/pg_subscription.c
index 9efc9159f2..b568fe3470 100644
--- a/src/backend/catalog/pg_subscription.c
+++ b/src/backend/catalog/pg_subscription.c
@@ -72,6 +72,7 @@ GetSubscription(Oid subid, bool missing_ok)
 	sub->passwordrequired = subform->subpasswordrequired;
 	sub->runasowner = subform->subrunasowner;
 	sub->failover = subform->subfailover;
+	sub->forcealter = subform->subforcealter;
 
 	/* Get conninfo */
 	datum = SysCacheGetAttrNotNull(SUBSCRIPTIONOID,
diff --git a/src/backend/catalog/system_views.sql b/src/backend/catalog/system_views.sql
index 19cabc9a47..b89eacc96b 100644
--- a/src/backend/catalog/system_views.sql
+++ b/src/backend/catalog/system_views.sql
@@ -1355,7 +1355,7 @@ REVOKE ALL ON pg_replication_origin_status FROM public;
 REVOKE ALL ON pg_subscription FROM public;
 GRANT SELECT (oid, subdbid, subskiplsn, subname, subowner, subenabled,
               subbinary, substream, subtwophasestate, subdisableonerr,
-			  subpasswordrequired, subrunasowner, subfailover,
+			  subpasswordrequired, subrunasowner, subfailover, subforcealter,
               subslotname, subsynccommit, subpublications, suborigin)
     ON pg_subscription TO public;
 
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index 401ea1dc88..9837ebd1c7 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -73,6 +73,7 @@
 #define SUBOPT_FAILOVER				0x00002000
 #define SUBOPT_LSN					0x00004000
 #define SUBOPT_ORIGIN				0x00008000
+#define SUBOPT_FORCE_ALTER			0x00010000
 
 /* check if the 'val' has 'bits' set */
 #define IsSet(val, bits)  (((val) & (bits)) == (bits))
@@ -100,6 +101,7 @@ typedef struct SubOpts
 	bool		failover;
 	char	   *origin;
 	XLogRecPtr	lsn;
+	bool		force_alter;
 } SubOpts;
 
 static List *fetch_table_list(WalReceiverConn *wrconn, List *publications);
@@ -162,6 +164,8 @@ parse_subscription_options(ParseState *pstate, List *stmt_options,
 		opts->failover = false;
 	if (IsSet(supported_opts, SUBOPT_ORIGIN))
 		opts->origin = pstrdup(LOGICALREP_ORIGIN_ANY);
+	if (IsSet(supported_opts, SUBOPT_FORCE_ALTER))
+		opts->force_alter = false;
 
 	/* Parse options */
 	foreach(lc, stmt_options)
@@ -355,6 +359,15 @@ parse_subscription_options(ParseState *pstate, List *stmt_options,
 			opts->specified_opts |= SUBOPT_LSN;
 			opts->lsn = lsn;
 		}
+		else if (IsSet(supported_opts, SUBOPT_FORCE_ALTER) &&
+				 strcmp(defel->defname, "force_alter") == 0)
+		{
+			if (IsSet(opts->specified_opts, SUBOPT_FORCE_ALTER))
+				errorConflictingDefElem(defel, pstate);
+
+			opts->specified_opts |= SUBOPT_FORCE_ALTER;
+			opts->force_alter = defGetBoolean(defel);
+		}
 		else
 			ereport(ERROR,
 					(errcode(ERRCODE_SYNTAX_ERROR),
@@ -592,7 +605,8 @@ CreateSubscription(ParseState *pstate, CreateSubscriptionStmt *stmt,
 					  SUBOPT_SYNCHRONOUS_COMMIT | SUBOPT_BINARY |
 					  SUBOPT_STREAMING | SUBOPT_TWOPHASE_COMMIT |
 					  SUBOPT_DISABLE_ON_ERR | SUBOPT_PASSWORD_REQUIRED |
-					  SUBOPT_RUN_AS_OWNER | SUBOPT_FAILOVER | SUBOPT_ORIGIN);
+					  SUBOPT_RUN_AS_OWNER | SUBOPT_FAILOVER | SUBOPT_ORIGIN |
+					  SUBOPT_FORCE_ALTER);
 	parse_subscription_options(pstate, stmt->options, supported_opts, &opts);
 
 	/*
@@ -699,6 +713,7 @@ CreateSubscription(ParseState *pstate, CreateSubscriptionStmt *stmt,
 	values[Anum_pg_subscription_subpasswordrequired - 1] = BoolGetDatum(opts.passwordrequired);
 	values[Anum_pg_subscription_subrunasowner - 1] = BoolGetDatum(opts.runasowner);
 	values[Anum_pg_subscription_subfailover - 1] = BoolGetDatum(opts.failover);
+	values[Anum_pg_subscription_subforcealter - 1] = BoolGetDatum(opts.force_alter);
 	values[Anum_pg_subscription_subconninfo - 1] =
 		CStringGetTextDatum(conninfo);
 	if (opts.slot_name)
@@ -1138,7 +1153,7 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 								  SUBOPT_DISABLE_ON_ERR |
 								  SUBOPT_PASSWORD_REQUIRED |
 								  SUBOPT_RUN_AS_OWNER | SUBOPT_FAILOVER |
-								  SUBOPT_ORIGIN);
+								  SUBOPT_ORIGIN | SUBOPT_FORCE_ALTER);
 
 				parse_subscription_options(pstate, stmt->options,
 										   supported_opts, &opts);
@@ -1207,6 +1222,23 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 						if (sub->twophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
 							(prepared_xacts = GetGidListBySubid(subid)) != NIL)
 						{
+							bool		raise_error =
+								IsSet(opts.specified_opts, SUBOPT_FORCE_ALTER) ?
+								!opts.force_alter : !sub->forcealter;
+
+							/*
+							 * Abort prepared transactions only if
+							 * 'force_alter' option is true. Otherwise raise
+							 * an ERROR.
+							 */
+							if (raise_error)
+								ereport(ERROR,
+										(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+										 errmsg("cannot alter %s when there are prepared transactions",
+												"two_phase = false"),
+										 errhint("Resolve these transactions or set %s, and then try again.",
+												 "force_alter = true")));
+
 							ereport(NOTICE,
 									(errmsg_plural("requested altering to %s but there is prepared transaction done by the subscription",
 												   "requested altering to %s but there are prepared transactions done by the subscription",
diff --git a/src/bin/pg_dump/pg_dump.c b/src/bin/pg_dump/pg_dump.c
index 5426f1177c..85c69a835b 100644
--- a/src/bin/pg_dump/pg_dump.c
+++ b/src/bin/pg_dump/pg_dump.c
@@ -4754,6 +4754,7 @@ getSubscriptions(Archive *fout)
 	int			i_suboriginremotelsn;
 	int			i_subenabled;
 	int			i_subfailover;
+	int			i_subforcealter;
 	int			i,
 				ntups;
 
@@ -4826,10 +4827,17 @@ getSubscriptions(Archive *fout)
 
 	if (fout->remoteVersion >= 170000)
 		appendPQExpBufferStr(query,
-							 " s.subfailover\n");
+							 " s.subfailover,\n");
 	else
 		appendPQExpBuffer(query,
-						  " false AS subfailover\n");
+						  " false AS subfailover,\n");
+
+	if (fout->remoteVersion >= 170000)
+		appendPQExpBufferStr(query,
+							 " s.subforcealter\n");
+	else
+		appendPQExpBuffer(query,
+						  " false AS subforcealter\n");
 
 	appendPQExpBufferStr(query,
 						 "FROM pg_subscription s\n");
@@ -4869,6 +4877,7 @@ getSubscriptions(Archive *fout)
 	i_suboriginremotelsn = PQfnumber(res, "suboriginremotelsn");
 	i_subenabled = PQfnumber(res, "subenabled");
 	i_subfailover = PQfnumber(res, "subfailover");
+	i_subforcealter = PQfnumber(res, "subforcealter");
 
 	subinfo = pg_malloc(ntups * sizeof(SubscriptionInfo));
 
@@ -4915,6 +4924,8 @@ getSubscriptions(Archive *fout)
 			pg_strdup(PQgetvalue(res, i, i_subenabled));
 		subinfo[i].subfailover =
 			pg_strdup(PQgetvalue(res, i, i_subfailover));
+		subinfo[i].subforcealter =
+			pg_strdup(PQgetvalue(res, i, i_subforcealter));
 
 		/* Decide whether we want to dump it */
 		selectDumpableObject(&(subinfo[i].dobj), fout);
@@ -5155,6 +5166,9 @@ dumpSubscription(Archive *fout, const SubscriptionInfo *subinfo)
 	if (strcmp(subinfo->subfailover, "t") == 0)
 		appendPQExpBufferStr(query, ", failover = true");
 
+	if (strcmp(subinfo->subforcealter, "t") == 0)
+		appendPQExpBufferStr(query, ", force_alter = true");
+
 	if (strcmp(subinfo->subsynccommit, "off") != 0)
 		appendPQExpBuffer(query, ", synchronous_commit = %s", fmtId(subinfo->subsynccommit));
 
diff --git a/src/bin/pg_dump/pg_dump.h b/src/bin/pg_dump/pg_dump.h
index 4b2e5870a9..8f5f9d13b9 100644
--- a/src/bin/pg_dump/pg_dump.h
+++ b/src/bin/pg_dump/pg_dump.h
@@ -671,6 +671,7 @@ typedef struct _SubscriptionInfo
 	char	   *suborigin;
 	char	   *suboriginremotelsn;
 	char	   *subfailover;
+	char	   *subforcealter;
 } SubscriptionInfo;
 
 /*
diff --git a/src/bin/psql/describe.c b/src/bin/psql/describe.c
index 7c9a1f234c..abf91a81fa 100644
--- a/src/bin/psql/describe.c
+++ b/src/bin/psql/describe.c
@@ -6539,7 +6539,7 @@ describeSubscriptions(const char *pattern, bool verbose)
 	printQueryOpt myopt = pset.popt;
 	static const bool translate_columns[] = {false, false, false, false,
 		false, false, false, false, false, false, false, false, false, false,
-	false};
+	false, false};
 
 	if (pset.sversion < 100000)
 	{
@@ -6608,6 +6608,11 @@ describeSubscriptions(const char *pattern, bool verbose)
 							  ", subfailover AS \"%s\"\n",
 							  gettext_noop("Failover"));
 
+		if (pset.sversion >= 170000)
+			appendPQExpBuffer(&buf,
+							  ", subforcealter AS \"%s\"\n",
+							  gettext_noop("Force alter"));
+
 		appendPQExpBuffer(&buf,
 						  ",  subsynccommit AS \"%s\"\n"
 						  ",  subconninfo AS \"%s\"\n",
diff --git a/src/include/catalog/pg_subscription.h b/src/include/catalog/pg_subscription.h
index 0aa14ec4a2..deac7aa943 100644
--- a/src/include/catalog/pg_subscription.h
+++ b/src/include/catalog/pg_subscription.h
@@ -98,6 +98,13 @@ CATALOG(pg_subscription,6100,SubscriptionRelationId) BKI_SHARED_RELATION BKI_ROW
 								 * slots) in the upstream database are enabled
 								 * to be synchronized to the standbys. */
 
+	bool		subforcealter;	/* True allows the ALTER SUBSCRIPTION command
+								 * to proceed under conditions that would
+								 * otherwise result in an error. Currently,
+								 * 'force_alter' only has an effect when
+								 * altering the two_phase option from "true"
+								 * to "false". */
+
 #ifdef CATALOG_VARLEN			/* variable-length fields start here */
 	/* Connection string to the publisher */
 	text		subconninfo BKI_FORCE_NOT_NULL;
@@ -151,6 +158,12 @@ typedef struct Subscription
 								 * (i.e. the main slot and the table sync
 								 * slots) in the upstream database are enabled
 								 * to be synchronized to the standbys. */
+	bool		forcealter;		/* True allows the ALTER SUBSCRIPTION command
+								 * to proceed under conditions that would
+								 * otherwise result in an error. Currently,
+								 * 'force_alter' only has an effect when
+								 * altering the two_phase option from "true"
+								 * to "false". */
 	char	   *conninfo;		/* Connection string to the publisher */
 	char	   *slotname;		/* Name of the replication slot */
 	char	   *synccommit;		/* Synchronous commit setting for worker */
diff --git a/src/test/regress/expected/subscription.out b/src/test/regress/expected/subscription.out
index 51fa4b9690..b36fc6b8f7 100644
--- a/src/test/regress/expected/subscription.out
+++ b/src/test/regress/expected/subscription.out
@@ -116,18 +116,18 @@ CREATE SUBSCRIPTION regress_testsub4 CONNECTION 'dbname=regress_doesnotexist' PU
 WARNING:  subscription was created, but is not connected
 HINT:  To initiate replication, you must manually create the replication slot, enable the subscription, and refresh the subscription.
 \dRs+ regress_testsub4
-                                                                                                                 List of subscriptions
-       Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
-------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub4 | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | none   | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                        List of subscriptions
+       Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub4 | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | none   | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub4 SET (origin = any);
 \dRs+ regress_testsub4
-                                                                                                                 List of subscriptions
-       Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
-------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub4 | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                        List of subscriptions
+       Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub4 | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 DROP SUBSCRIPTION regress_testsub3;
@@ -145,10 +145,10 @@ ALTER SUBSCRIPTION regress_testsub CONNECTION 'foobar';
 ERROR:  invalid connection string syntax: missing "=" after "foobar" in connection info string
 
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET PUBLICATION testpub2, testpub3 WITH (refresh = false);
@@ -157,10 +157,10 @@ ALTER SUBSCRIPTION regress_testsub SET (slot_name = 'newname');
 ALTER SUBSCRIPTION regress_testsub SET (password_required = false);
 ALTER SUBSCRIPTION regress_testsub SET (run_as_owner = true);
 \dRs+
-                                                                                                                     List of subscriptions
-      Name       |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |           Conninfo           | Skip LSN 
------------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+------------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | f                 | t             | f        | off                | dbname=regress_doesnotexist2 | 0/0
+                                                                                                                            List of subscriptions
+      Name       |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |           Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+------------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | f                 | t             | f        | f           | off                | dbname=regress_doesnotexist2 | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (password_required = true);
@@ -176,10 +176,10 @@ ERROR:  unrecognized subscription parameter: "create_slot"
 -- ok
 ALTER SUBSCRIPTION regress_testsub SKIP (lsn = '0/12345');
 \dRs+
-                                                                                                                     List of subscriptions
-      Name       |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |           Conninfo           | Skip LSN 
------------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+------------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist2 | 0/12345
+                                                                                                                            List of subscriptions
+      Name       |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |           Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+------------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist2 | 0/12345
 (1 row)
 
 -- ok - with lsn = NONE
@@ -188,10 +188,10 @@ ALTER SUBSCRIPTION regress_testsub SKIP (lsn = NONE);
 ALTER SUBSCRIPTION regress_testsub SKIP (lsn = '0/0');
 ERROR:  invalid WAL location (LSN): 0/0
 \dRs+
-                                                                                                                     List of subscriptions
-      Name       |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |           Conninfo           | Skip LSN 
------------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+------------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist2 | 0/0
+                                                                                                                            List of subscriptions
+      Name       |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |           Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+------------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist2 | 0/0
 (1 row)
 
 BEGIN;
@@ -223,10 +223,10 @@ ALTER SUBSCRIPTION regress_testsub_foo SET (synchronous_commit = foobar);
 ERROR:  invalid value for parameter "synchronous_commit": "foobar"
 HINT:  Available values: local, remote_write, remote_apply, on, off.
 \dRs+
-                                                                                                                       List of subscriptions
-        Name         |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |           Conninfo           | Skip LSN 
----------------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+------------------------------+----------
- regress_testsub_foo | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | t                 | f             | f        | local              | dbname=regress_doesnotexist2 | 0/0
+                                                                                                                              List of subscriptions
+        Name         |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |           Conninfo           | Skip LSN 
+---------------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+------------------------------+----------
+ regress_testsub_foo | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | t                 | f             | f        | f           | local              | dbname=regress_doesnotexist2 | 0/0
 (1 row)
 
 -- rename back to keep the rest simple
@@ -255,19 +255,19 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 WARNING:  subscription was created, but is not connected
 HINT:  To initiate replication, you must manually create the replication slot, enable the subscription, and refresh the subscription.
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | t      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | t      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (binary = false);
 ALTER SUBSCRIPTION regress_testsub SET (slot_name = NONE);
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 DROP SUBSCRIPTION regress_testsub;
@@ -279,27 +279,27 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 WARNING:  subscription was created, but is not connected
 HINT:  To initiate replication, you must manually create the replication slot, enable the subscription, and refresh the subscription.
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | on        | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | on        | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (streaming = parallel);
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | parallel  | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | parallel  | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (streaming = false);
 ALTER SUBSCRIPTION regress_testsub SET (slot_name = NONE);
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 -- fail - publication already exists
@@ -314,10 +314,10 @@ ALTER SUBSCRIPTION regress_testsub ADD PUBLICATION testpub1, testpub2 WITH (refr
 ALTER SUBSCRIPTION regress_testsub ADD PUBLICATION testpub1, testpub2 WITH (refresh = false);
 ERROR:  publication "testpub1" is already in subscription "regress_testsub"
 \dRs+
-                                                                                                                        List of subscriptions
-      Name       |           Owner           | Enabled |         Publication         | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-----------------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub,testpub1,testpub2} | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                               List of subscriptions
+      Name       |           Owner           | Enabled |         Publication         | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-----------------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub,testpub1,testpub2} | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 -- fail - publication used more than once
@@ -332,10 +332,10 @@ ERROR:  publication "testpub3" is not in subscription "regress_testsub"
 -- ok - delete publications
 ALTER SUBSCRIPTION regress_testsub DROP PUBLICATION testpub1, testpub2 WITH (refresh = false);
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 DROP SUBSCRIPTION regress_testsub;
@@ -371,19 +371,19 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 WARNING:  subscription was created, but is not connected
 HINT:  To initiate replication, you must manually create the replication slot, enable the subscription, and refresh the subscription.
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | p                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | p                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 -- We can alter streaming when two_phase enabled
 ALTER SUBSCRIPTION regress_testsub SET (streaming = true);
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | on        | p                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | on        | p                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (slot_name = NONE);
@@ -393,10 +393,10 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 WARNING:  subscription was created, but is not connected
 HINT:  To initiate replication, you must manually create the replication slot, enable the subscription, and refresh the subscription.
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | on        | p                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | on        | p                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (slot_name = NONE);
@@ -409,18 +409,18 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 WARNING:  subscription was created, but is not connected
 HINT:  To initiate replication, you must manually create the replication slot, enable the subscription, and refresh the subscription.
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (disable_on_error = true);
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | t                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | t                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (slot_name = NONE);
diff --git a/src/test/subscription/t/021_twophase.pl b/src/test/subscription/t/021_twophase.pl
index c3e15e537b..d58b046571 100644
--- a/src/test/subscription/t/021_twophase.pl
+++ b/src/test/subscription/t/021_twophase.pl
@@ -472,15 +472,36 @@ $result = $node_subscriber->safe_psql('postgres',
 	"SELECT count(*) FROM pg_prepared_xacts;");
 is($result, q(1), "transaction has been prepared on subscriber");
 
-# Toggle the two_phase to "false" before the COMMIT PREPARED
+# Disable the subscription to alter the two_phase option
 $node_subscriber->safe_psql('postgres',
 	"ALTER SUBSCRIPTION tap_sub_copy DISABLE;");
 $node_subscriber->poll_query_until('postgres',
 	"SELECT count(*) = 0 FROM pg_stat_activity WHERE backend_type = 'logical replication worker'"
 );
+
+# Try altering the two_phase option to "false". The command will fail since
+# there is a prepared transaction and the 'force_alter' option is not specified
+# as true.
+
+my $stdout;
+my $stderr;
+
+($result, $stdout, $stderr) = $node_subscriber->psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = false);");
+ok( $stderr =~
+	  /cannot alter two_phase = false when there are prepared transactions/,
+	'ALTER SUBSCRIPTION failed');
+
+# Verify the prepared transaction still exists
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT count(*) FROM pg_prepared_xacts;");
+is($result, q(1), "prepared transaction still exists");
+
+# Alter the two_phase true to false with the force_alter option enabled. This
+# command will succeed after aborting the prepared transaction.
 $node_subscriber->safe_psql(
 	'postgres', "
-    ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = false);
+	ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = false, force_alter = true);
     ALTER SUBSCRIPTION tap_sub_copy ENABLE;");
 
 # Verify any prepared transactions are aborted because two_phase is changed to
-- 
2.43.0

From 156c14b89aa41d00beda13e1d1980f2448f57881 Mon Sep 17 00:00:00 2001
From: Ajin Cherian <ajinc@fast.au.fujitsu.com>
Date: Fri, 5 Apr 2024 06:47:18 -0400
Subject: [PATCH v16 1/4] Allow altering of two_phase option of a SUBSCRIPTION

This patch allows the user to alter the 'two_phase' option of a subscriber provided no
uncommitted prepared transactions are pending on that subscription.

Author: Cherian Ajin, Hayato Kuroda
---
 doc/src/sgml/ref/alter_subscription.sgml      | 12 ++-
 src/backend/access/transam/twophase.c         | 62 +++++++++++++
 src/backend/commands/subscriptioncmds.c       | 88 ++++++++++++++-----
 .../libpqwalreceiver/libpqwalreceiver.c       |  9 +-
 src/backend/replication/logical/launcher.c    | 12 ++-
 src/backend/replication/logical/worker.c      | 25 +-----
 src/backend/replication/slot.c                | 18 +++-
 src/backend/replication/walsender.c           | 18 +++-
 src/bin/psql/tab-complete.c                   |  2 +-
 src/include/access/twophase.h                 |  5 ++
 src/include/replication/slot.h                |  3 +-
 src/include/replication/walreceiver.h         | 11 +--
 src/include/replication/worker_internal.h     |  3 +-
 src/test/regress/expected/subscription.out    |  5 +-
 src/test/regress/sql/subscription.sql         |  5 +-
 src/test/subscription/t/021_twophase.pl       | 77 +++++++++++++++-
 16 files changed, 279 insertions(+), 76 deletions(-)

diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index 476f195622..0b23df1b77 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -68,8 +68,9 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
   <para>
    Commands <command>ALTER SUBSCRIPTION ... REFRESH PUBLICATION</command>,
    <command>ALTER SUBSCRIPTION ... {SET|ADD|DROP} PUBLICATION ...</command>
-   with <literal>refresh</literal> option as <literal>true</literal> and
-   <command>ALTER SUBSCRIPTION ... SET (failover = true|false)</command>
+   with <literal>refresh</literal> option as <literal>true</literal>,
+   <command>ALTER SUBSCRIPTION ... SET (failover = true|false)</command> and
+   <command>ALTER SUBSCRIPTION ... SET (two_phase = true|false)</command>
    cannot be executed inside a transaction block.
 
    These commands also cannot be executed when the subscription has
@@ -228,9 +229,12 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-disable-on-error"><literal>disable_on_error</literal></link>,
       <link linkend="sql-createsubscription-params-with-password-required"><literal>password_required</literal></link>,
       <link linkend="sql-createsubscription-params-with-run-as-owner"><literal>run_as_owner</literal></link>,
-      <link linkend="sql-createsubscription-params-with-origin"><literal>origin</literal></link>, and
-      <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>.
+      <link linkend="sql-createsubscription-params-with-origin"><literal>origin</literal></link>,
+      <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>, and
+      <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>.
       Only a superuser can set <literal>password_required = false</literal>.
+      The <literal>two_phase</literal> parameter can only be altered when the
+      subscription is disabled.
      </para>
 
      <para>
diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index 9a8257fcaf..35bce6809d 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -2681,3 +2681,65 @@ LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 	LWLockRelease(TwoPhaseStateLock);
 	return found;
 }
+
+/*
+ * TwoPhaseTransactionGid
+ *		Form the prepared transaction GID for two_phase transactions.
+ *
+ * Return the GID in the supplied buffer.
+ */
+void
+TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid, int szgid)
+{
+	Assert(subid != InvalidRepOriginId);
+
+	if (!TransactionIdIsValid(xid))
+		ereport(ERROR,
+				(errcode(ERRCODE_PROTOCOL_VIOLATION),
+				 errmsg_internal("invalid two-phase transaction ID")));
+
+	snprintf(gid, szgid, "pg_gid_%u_%u", subid, xid);
+}
+
+/*
+ * IsTwoPhaseTransactionGidForSubid
+ *		Check whether the given GID (as formed by TwoPhaseTransactionGid) is
+ *		for the specified 'subid'.
+ */
+static bool
+IsTwoPhaseTransactionGidForSubid(Oid subid, char *gid)
+{
+	int			ret;
+	Oid			subid_written;
+	TransactionId xid;
+
+	ret = sscanf(gid, "pg_gid_%u_%u", &subid_written, &xid);
+
+	return (ret == 2 && subid == subid_written);
+}
+
+/*
+ * LookupGXactBySubid
+ *		Check if the prepared transaction done by apply worker exists.
+ */
+bool
+LookupGXactBySubid(Oid subid)
+{
+	bool		found = false;
+
+	LWLockAcquire(TwoPhaseStateLock, LW_SHARED);
+	for (int i = 0; i < TwoPhaseState->numPrepXacts; i++)
+	{
+		GlobalTransaction gxact = TwoPhaseState->prepXacts[i];
+
+		/* Ignore not-yet-valid GIDs. */
+		if (gxact->valid &&
+			IsTwoPhaseTransactionGidForSubid(subid, gxact->gid))
+		{
+			found = true;
+			break;
+		}
+	}
+	LWLockRelease(TwoPhaseStateLock);
+	return found;
+}
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index e407428dbc..61fd74c971 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -16,6 +16,7 @@
 
 #include "access/htup_details.h"
 #include "access/table.h"
+#include "access/twophase.h"
 #include "access/xact.h"
 #include "catalog/catalog.h"
 #include "catalog/dependency.h"
@@ -259,21 +260,9 @@ parse_subscription_options(ParseState *pstate, List *stmt_options,
 			opts->specified_opts |= SUBOPT_STREAMING;
 			opts->streaming = defGetStreamingMode(defel);
 		}
-		else if (strcmp(defel->defname, "two_phase") == 0)
+		else if (IsSet(supported_opts, SUBOPT_TWOPHASE_COMMIT) &&
+				 strcmp(defel->defname, "two_phase") == 0)
 		{
-			/*
-			 * Do not allow toggling of two_phase option. Doing so could cause
-			 * missing of transactions and lead to an inconsistent replica.
-			 * See comments atop worker.c
-			 *
-			 * Note: Unsupported twophase indicates that this call originated
-			 * from AlterSubscription.
-			 */
-			if (!IsSet(supported_opts, SUBOPT_TWOPHASE_COMMIT))
-				ereport(ERROR,
-						(errcode(ERRCODE_SYNTAX_ERROR),
-						 errmsg("unrecognized subscription parameter: \"%s\"", defel->defname)));
-
 			if (IsSet(opts->specified_opts, SUBOPT_TWOPHASE_COMMIT))
 				errorConflictingDefElem(defel, pstate);
 
@@ -1143,7 +1132,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 			{
 				supported_opts = (SUBOPT_SLOT_NAME |
 								  SUBOPT_SYNCHRONOUS_COMMIT | SUBOPT_BINARY |
-								  SUBOPT_STREAMING | SUBOPT_DISABLE_ON_ERR |
+								  SUBOPT_STREAMING | SUBOPT_TWOPHASE_COMMIT |
+								  SUBOPT_DISABLE_ON_ERR |
 								  SUBOPT_PASSWORD_REQUIRED |
 								  SUBOPT_RUN_AS_OWNER | SUBOPT_FAILOVER |
 								  SUBOPT_ORIGIN);
@@ -1151,6 +1141,65 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 				parse_subscription_options(pstate, stmt->options,
 										   supported_opts, &opts);
 
+				if (IsSet(opts.specified_opts, SUBOPT_TWOPHASE_COMMIT))
+				{
+					/*
+					 * Do not allow changing the two_phase option if the
+					 * subscription is enabled. This is because the two_phase
+					 * option of the slot on the publisher cannot be modified
+					 * if the slot is currently acquired by the apply worker.
+					 */
+					if (form->subenabled)
+						ereport(ERROR,
+								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+								 errmsg("cannot set %s for enabled subscription",
+										"two_phase")));
+
+					if (!sub->slotname)
+						ereport(ERROR,
+								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+								 errmsg("cannot set %s for a subscription that does not have a slot name",
+										"two_phase")));
+
+					/*
+					 * Workers may still survive even if the subscription has
+					 * been disabled. They may read the pg_subscription
+					 * catalog and detect that the twophase parameter is
+					 * updated, which causes the assertion failure. Ensure
+					 * workers have already been exited to avoid it.
+					 */
+					if (logicalrep_workers_find(subid, true, true))
+						ereport(ERROR,
+								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+								 errmsg("cannot alter two_phase when logical replication worker is still running"),
+								 errhint("Wait certain time and try again.")));
+
+					/*
+					 * two_phase cannot be disabled if there are any
+					 * uncommitted prepared transactions present.
+					 */
+					if (!opts.twophase &&
+						form->subtwophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
+						LookupGXactBySubid(subid))
+						ereport(ERROR,
+								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+								 errmsg("cannot disable two_phase when uncommitted prepared transactions present"),
+								 errhint("Resolve these transactions and try again")));
+
+					/*
+					 * The changed two_phase option of the slot can't be
+					 * rolled back.
+					 */
+					PreventInTransactionBlock(isTopLevel, "ALTER SUBSCRIPTION ... SET (two_phase)");
+
+					/* Change system catalog acoordingly */
+					values[Anum_pg_subscription_subtwophasestate - 1] =
+						CharGetDatum(opts.twophase ?
+									 LOGICALREP_TWOPHASE_STATE_PENDING :
+									 LOGICALREP_TWOPHASE_STATE_DISABLED);
+					replaces[Anum_pg_subscription_subtwophasestate - 1] = true;
+				}
+
 				if (IsSet(opts.specified_opts, SUBOPT_SLOT_NAME))
 				{
 					/*
@@ -1505,7 +1554,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 	 * doing the database operations we won't be able to rollback altered
 	 * slot.
 	 */
-	if (replaces[Anum_pg_subscription_subfailover - 1])
+	if (replaces[Anum_pg_subscription_subfailover - 1] ||
+		replaces[Anum_pg_subscription_subtwophasestate - 1])
 	{
 		bool		must_use_password;
 		char	   *err;
@@ -1525,7 +1575,7 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 
 		PG_TRY();
 		{
-			walrcv_alter_slot(wrconn, sub->slotname, opts.failover);
+			walrcv_alter_slot(wrconn, sub->slotname, opts.failover, opts.twophase);
 		}
 		PG_FINALLY();
 		{
@@ -1672,9 +1722,7 @@ DropSubscription(DropSubscriptionStmt *stmt, bool isTopLevel)
 	 * New workers won't be started because we hold an exclusive lock on the
 	 * subscription till the end of the transaction.
 	 */
-	LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
-	subworkers = logicalrep_workers_find(subid, false);
-	LWLockRelease(LogicalRepWorkerLock);
+	subworkers = logicalrep_workers_find(subid, false, true);
 	foreach(lc, subworkers)
 	{
 		LogicalRepWorker *w = (LogicalRepWorker *) lfirst(lc);
diff --git a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
index 02f12f2921..2f035a0c3c 100644
--- a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
+++ b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
@@ -80,7 +80,7 @@ static char *libpqrcv_create_slot(WalReceiverConn *conn,
 								  CRSSnapshotAction snapshot_action,
 								  XLogRecPtr *lsn);
 static void libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-								bool failover);
+								bool failover, bool two_phase);
 static pid_t libpqrcv_get_backend_pid(WalReceiverConn *conn);
 static WalRcvExecResult *libpqrcv_exec(WalReceiverConn *conn,
 									   const char *query,
@@ -1121,15 +1121,16 @@ libpqrcv_create_slot(WalReceiverConn *conn, const char *slotname,
  */
 static void
 libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-					bool failover)
+					bool failover, bool two_phase)
 {
 	StringInfoData cmd;
 	PGresult   *res;
 
 	initStringInfo(&cmd);
-	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( FAILOVER %s )",
+	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( FAILOVER %s, TWO_PHASE %s )",
 					 quote_identifier(slotname),
-					 failover ? "true" : "false");
+					 failover ? "true" : "false",
+					 two_phase ? "true" : "false");
 
 	res = libpqrcv_PQexec(conn->streamConn, cmd.data);
 	pfree(cmd.data);
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 27c3a91fb7..45744b771f 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -272,12 +272,15 @@ logicalrep_worker_find(Oid subid, Oid relid, bool only_running)
  * the subscription, instead of just one.
  */
 List *
-logicalrep_workers_find(Oid subid, bool only_running)
+logicalrep_workers_find(Oid subid, bool only_running, bool require_lock)
 {
 	int			i;
 	List	   *res = NIL;
 
-	Assert(LWLockHeldByMe(LogicalRepWorkerLock));
+	if (require_lock)
+		LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
+	else
+		Assert(LWLockHeldByMe(LogicalRepWorkerLock));
 
 	/* Search for attached worker for a given subscription id. */
 	for (i = 0; i < max_logical_replication_workers; i++)
@@ -288,6 +291,9 @@ logicalrep_workers_find(Oid subid, bool only_running)
 			res = lappend(res, w);
 	}
 
+	if (require_lock)
+		LWLockRelease(LogicalRepWorkerLock);
+
 	return res;
 }
 
@@ -759,7 +765,7 @@ logicalrep_worker_detach(void)
 
 		LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
 
-		workers = logicalrep_workers_find(MyLogicalRepWorker->subid, true);
+		workers = logicalrep_workers_find(MyLogicalRepWorker->subid, true, false);
 		foreach(lc, workers)
 		{
 			LogicalRepWorker *w = (LogicalRepWorker *) lfirst(lc);
diff --git a/src/backend/replication/logical/worker.c b/src/backend/replication/logical/worker.c
index 3b285894db..33bfeb1fb2 100644
--- a/src/backend/replication/logical/worker.c
+++ b/src/backend/replication/logical/worker.c
@@ -401,9 +401,6 @@ static void apply_handle_tuple_routing(ApplyExecutionData *edata,
 									   LogicalRepTupleData *newtup,
 									   CmdType operation);
 
-/* Compute GID for two_phase transactions */
-static void TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid, int szgid);
-
 /* Functions for skipping changes */
 static void maybe_start_skipping_changes(XLogRecPtr finish_lsn);
 static void stop_skipping_changes(void);
@@ -3911,7 +3908,7 @@ maybe_reread_subscription(void)
 	/* !slotname should never happen when enabled is true. */
 	Assert(newsub->slotname);
 
-	/* two-phase should not be altered */
+	/* two-phase cannot be altered while the worker exists */
 	Assert(newsub->twophasestate == MySubscription->twophasestate);
 
 	/*
@@ -4396,24 +4393,6 @@ cleanup_subxact_info()
 	subxact_data.nsubxacts_max = 0;
 }
 
-/*
- * Form the prepared transaction GID for two_phase transactions.
- *
- * Return the GID in the supplied buffer.
- */
-static void
-TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid, int szgid)
-{
-	Assert(subid != InvalidRepOriginId);
-
-	if (!TransactionIdIsValid(xid))
-		ereport(ERROR,
-				(errcode(ERRCODE_PROTOCOL_VIOLATION),
-				 errmsg_internal("invalid two-phase transaction ID")));
-
-	snprintf(gid, szgid, "pg_gid_%u_%u", subid, xid);
-}
-
 /*
  * Common function to run the apply loop with error handling. Disable the
  * subscription, if necessary.
@@ -5013,7 +4992,7 @@ AtEOXact_LogicalRepWorkers(bool isCommit)
 			List	   *workers;
 			ListCell   *lc2;
 
-			workers = logicalrep_workers_find(subid, true);
+			workers = logicalrep_workers_find(subid, true, false);
 			foreach(lc2, workers)
 			{
 				LogicalRepWorker *worker = (LogicalRepWorker *) lfirst(lc2);
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index baf9b89dc4..2ad6dca993 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -804,8 +804,10 @@ ReplicationSlotDrop(const char *name, bool nowait)
  * Change the definition of the slot identified by the specified name.
  */
 void
-ReplicationSlotAlter(const char *name, bool failover)
+ReplicationSlotAlter(const char *name, bool failover, bool two_phase)
 {
+	bool		update_slot = false;
+
 	Assert(MyReplicationSlot == NULL);
 
 	ReplicationSlotAcquire(name, false);
@@ -854,6 +856,20 @@ ReplicationSlotAlter(const char *name, bool failover)
 		MyReplicationSlot->data.failover = failover;
 		SpinLockRelease(&MyReplicationSlot->mutex);
 
+		update_slot = true;
+	}
+
+	if (MyReplicationSlot->data.two_phase != two_phase)
+	{
+		SpinLockAcquire(&MyReplicationSlot->mutex);
+		MyReplicationSlot->data.two_phase = two_phase;
+		SpinLockRelease(&MyReplicationSlot->mutex);
+
+		update_slot = true;
+	}
+
+	if (update_slot)
+	{
 		ReplicationSlotMarkDirty();
 		ReplicationSlotSave();
 	}
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 754f505c13..af776fccb8 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1409,9 +1409,11 @@ DropReplicationSlot(DropReplicationSlotCmd *cmd)
  * Process extra options given to ALTER_REPLICATION_SLOT.
  */
 static void
-ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd, bool *failover)
+ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd,
+						  bool *failover, bool *two_phase)
 {
 	bool		failover_given = false;
+	bool		two_phase_given = false;
 
 	/* Parse options */
 	foreach_ptr(DefElem, defel, cmd->options)
@@ -1425,6 +1427,15 @@ ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd, bool *failover)
 			failover_given = true;
 			*failover = defGetBoolean(defel);
 		}
+		else if (strcmp(defel->defname, "two_phase") == 0)
+		{
+			if (two_phase_given)
+				ereport(ERROR,
+						(errcode(ERRCODE_SYNTAX_ERROR),
+						 errmsg("conflicting or redundant options")));
+			two_phase_given = true;
+			*two_phase = defGetBoolean(defel);
+		}
 		else
 			elog(ERROR, "unrecognized option: %s", defel->defname);
 	}
@@ -1437,9 +1448,10 @@ static void
 AlterReplicationSlot(AlterReplicationSlotCmd *cmd)
 {
 	bool		failover = false;
+	bool		two_phase = false;
 
-	ParseAlterReplSlotOptions(cmd, &failover);
-	ReplicationSlotAlter(cmd->slotname, failover);
+	ParseAlterReplSlotOptions(cmd, &failover, &two_phase);
+	ReplicationSlotAlter(cmd->slotname, failover, two_phase);
 }
 
 /*
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
index d453e224d9..891face1b6 100644
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -1948,7 +1948,7 @@ psql_completion(const char *text, int start, int end)
 	else if (HeadMatches("ALTER", "SUBSCRIPTION", MatchAny) && TailMatches("SET", "("))
 		COMPLETE_WITH("binary", "disable_on_error", "failover", "origin",
 					  "password_required", "run_as_owner", "slot_name",
-					  "streaming", "synchronous_commit");
+					  "streaming", "synchronous_commit", "two_phase");
 	/* ALTER SUBSCRIPTION <name> SKIP ( */
 	else if (HeadMatches("ALTER", "SUBSCRIPTION", MatchAny) && TailMatches("SKIP", "("))
 		COMPLETE_WITH("lsn");
diff --git a/src/include/access/twophase.h b/src/include/access/twophase.h
index 56248c0006..d37e06fdee 100644
--- a/src/include/access/twophase.h
+++ b/src/include/access/twophase.h
@@ -62,4 +62,9 @@ extern void PrepareRedoRemove(TransactionId xid, bool giveWarning);
 extern void restoreTwoPhaseData(void);
 extern bool LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 						TimestampTz origin_prepare_timestamp);
+
+extern void TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid,
+								   int szgid);
+extern bool LookupGXactBySubid(Oid subid);
+
 #endif							/* TWOPHASE_H */
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index c9675ee87c..163a4a911a 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -243,7 +243,8 @@ extern void ReplicationSlotCreate(const char *name, bool db_specific,
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
 extern void ReplicationSlotDropAcquired(void);
-extern void ReplicationSlotAlter(const char *name, bool failover);
+extern void ReplicationSlotAlter(const char *name, bool failover,
+								 bool two_phase);
 
 extern void ReplicationSlotAcquire(const char *name, bool nowait);
 extern void ReplicationSlotRelease(void);
diff --git a/src/include/replication/walreceiver.h b/src/include/replication/walreceiver.h
index 12f71fa99b..31fa1257ec 100644
--- a/src/include/replication/walreceiver.h
+++ b/src/include/replication/walreceiver.h
@@ -372,12 +372,13 @@ typedef char *(*walrcv_create_slot_fn) (WalReceiverConn *conn,
 /*
  * walrcv_alter_slot_fn
  *
- * Change the definition of a replication slot. Currently, it only supports
- * changing the failover property of the slot.
+ * Change the definition of a replication slot. Currently, it supports
+ * changing the failover and the two_phase property of the slot.
  */
 typedef void (*walrcv_alter_slot_fn) (WalReceiverConn *conn,
 									  const char *slotname,
-									  bool failover);
+									  bool failover,
+									  bool two_phase);
 
 /*
  * walrcv_get_backend_pid_fn
@@ -455,8 +456,8 @@ extern PGDLLIMPORT WalReceiverFunctionsType *WalReceiverFunctions;
 	WalReceiverFunctions->walrcv_send(conn, buffer, nbytes)
 #define walrcv_create_slot(conn, slotname, temporary, two_phase, failover, snapshot_action, lsn) \
 	WalReceiverFunctions->walrcv_create_slot(conn, slotname, temporary, two_phase, failover, snapshot_action, lsn)
-#define walrcv_alter_slot(conn, slotname, failover) \
-	WalReceiverFunctions->walrcv_alter_slot(conn, slotname, failover)
+#define walrcv_alter_slot(conn, slotname, failover, two_phase) \
+	WalReceiverFunctions->walrcv_alter_slot(conn, slotname, failover, two_phase)
 #define walrcv_get_backend_pid(conn) \
 	WalReceiverFunctions->walrcv_get_backend_pid(conn)
 #define walrcv_exec(conn, exec, nRetTypes, retTypes) \
diff --git a/src/include/replication/worker_internal.h b/src/include/replication/worker_internal.h
index 515aefd519..990f5242f9 100644
--- a/src/include/replication/worker_internal.h
+++ b/src/include/replication/worker_internal.h
@@ -240,7 +240,8 @@ extern PGDLLIMPORT bool InitializingApplyWorker;
 extern void logicalrep_worker_attach(int slot);
 extern LogicalRepWorker *logicalrep_worker_find(Oid subid, Oid relid,
 												bool only_running);
-extern List *logicalrep_workers_find(Oid subid, bool only_running);
+extern List *logicalrep_workers_find(Oid subid, bool only_running,
+									 bool require_lock);
 extern bool logicalrep_worker_launch(LogicalRepWorkerType wtype,
 									 Oid dbid, Oid subid, const char *subname,
 									 Oid userid, Oid relid,
diff --git a/src/test/regress/expected/subscription.out b/src/test/regress/expected/subscription.out
index 0f2a25cdc1..51fa4b9690 100644
--- a/src/test/regress/expected/subscription.out
+++ b/src/test/regress/expected/subscription.out
@@ -377,10 +377,7 @@ HINT:  To initiate replication, you must manually create the replication slot, e
  regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | p                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
---fail - alter of two_phase option not supported.
-ALTER SUBSCRIPTION regress_testsub SET (two_phase = false);
-ERROR:  unrecognized subscription parameter: "two_phase"
--- but can alter streaming when two_phase enabled
+-- We can alter streaming when two_phase enabled
 ALTER SUBSCRIPTION regress_testsub SET (streaming = true);
 \dRs+
                                                                                                                 List of subscriptions
diff --git a/src/test/regress/sql/subscription.sql b/src/test/regress/sql/subscription.sql
index 3e5ba4cb8c..a3886d79ca 100644
--- a/src/test/regress/sql/subscription.sql
+++ b/src/test/regress/sql/subscription.sql
@@ -256,10 +256,7 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUBLICATION testpub WITH (connect = false, two_phase = true);
 
 \dRs+
---fail - alter of two_phase option not supported.
-ALTER SUBSCRIPTION regress_testsub SET (two_phase = false);
-
--- but can alter streaming when two_phase enabled
+-- We can alter streaming when two_phase enabled
 ALTER SUBSCRIPTION regress_testsub SET (streaming = true);
 
 \dRs+
diff --git a/src/test/subscription/t/021_twophase.pl b/src/test/subscription/t/021_twophase.pl
index 9437cd4c3b..4e8f627f7b 100644
--- a/src/test/subscription/t/021_twophase.pl
+++ b/src/test/subscription/t/021_twophase.pl
@@ -367,6 +367,81 @@ $result =
   $node_subscriber->safe_psql('postgres', "SELECT count(*) FROM tab_copy;");
 is($result, qq(2), 'replicated data in subscriber table');
 
+# Clean up
+$node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub");
+
+###############################
+# Disable the subscription and alter it to two_phase = false,
+# then verify that the altered subscription reflects the two_phase option.
+###############################
+
+# Alter subscription two_phase to false
+$node_subscriber->safe_psql('postgres',
+    "ALTER SUBSCRIPTION tap_sub_copy DISABLE;");
+$node_subscriber->poll_query_until('postgres',
+    "SELECT count(*) = 0 FROM pg_stat_activity WHERE backend_type = 'logical replication worker'"
+);
+$node_subscriber->safe_psql(
+	'postgres', "
+    ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = false);
+    ALTER SUBSCRIPTION tap_sub_copy ENABLE;");
+
+# Wait for subscription startup
+$node_subscriber->wait_for_subscription_sync($node_publisher, $appname_copy);
+
+# Make sure that the two-phase is disabled on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT subtwophasestate FROM pg_subscription WHERE subname = 'tap_sub_copy';"
+);
+is($result, qq(d), 'two-phase should be disabled');
+
+# Now do a prepare on the publisher and make sure that it is not replicated.
+$node_publisher->safe_psql(
+	'postgres', qq{
+    BEGIN;
+    INSERT INTO tab_copy VALUES (100);
+    PREPARE TRANSACTION 'newgid';
+	});
+
+# Wait for the subscriber to catchup
+$node_publisher->wait_for_catchup($appname_copy);
+
+# Make sure there are no prepared transactions on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT count(*) FROM pg_prepared_xacts;");
+is($result, qq(0), 'should be no prepared transactions on subscriber');
+
+# Now commit the insert and verify that it is replicated
+$node_publisher->safe_psql('postgres', "COMMIT PREPARED 'newgid';");
+
+# Wait for the subscriber to catchup
+$node_publisher->wait_for_catchup($appname_copy);
+
+# Make sure that the committed transaction is replicated.
+$result =
+  $node_subscriber->safe_psql('postgres', "SELECT count(*) FROM tab_copy;");
+is($result, qq(3), 'replicated data in subscriber table');
+
+# Alter subscription two_phase to true
+$node_subscriber->safe_psql('postgres',
+    "ALTER SUBSCRIPTION tap_sub_copy DISABLE;");
+$node_subscriber->poll_query_until('postgres',
+    "SELECT count(*) = 0 FROM pg_stat_activity WHERE backend_type = 'logical replication worker'"
+);
+$node_subscriber->safe_psql(
+	'postgres', "
+    ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = true);
+    ALTER SUBSCRIPTION tap_sub_copy ENABLE;");
+
+# Wait for subscription startup
+$node_subscriber->wait_for_subscription_sync($node_publisher, $appname_copy);
+
+# Make sure that the two-phase is enabled on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT subtwophasestate FROM pg_subscription WHERE subname = 'tap_sub_copy';"
+);
+is($result, qq(e), 'two-phase should be enabled');
+
 $node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub_copy;");
 $node_publisher->safe_psql('postgres', "DROP PUBLICATION tap_pub_copy;");
 
@@ -374,8 +449,6 @@ $node_publisher->safe_psql('postgres', "DROP PUBLICATION tap_pub_copy;");
 # check all the cleanup
 ###############################
 
-$node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub");
-
 $result = $node_subscriber->safe_psql('postgres',
 	"SELECT count(*) FROM pg_subscription");
 is($result, qq(0), 'check subscription was dropped on subscriber');
-- 
2.43.0

From 56c101260763ebd1806be65a3c8e90c1fb097751 Mon Sep 17 00:00:00 2001
From: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Date: Wed, 17 Apr 2024 06:18:23 +0000
Subject: [PATCH v16 2/4] Alter slot option two_phase only when altering "true"
 to "false"

Since the two_phase option is controlled by both the publisher (as a slot option)
and the subscriber (as a subscription option), the slot option must also be
modified.

Regarding the false->true case, the backend process alters the subtwophase to
LOGICALREP_TWOPHASE_STATE_PENDING once. After the subscription is enabled, a new
logical replication worker requests to change the two_phase option of its slot
from pending to true after the initial data synchronization is done. The code
path is the same as the case in which two_phase is initially set to true, so
there is no need to do something remarkable. However, for the true->false case,
the backend must connect to the publisher and expressly change the parameter
because the apply worker does not alter the option to false. Because this
operation cannot be rolled back, altering the two_phase parameter from "true"
to "false" within a transaction is prohibited.
---
 doc/src/sgml/ref/alter_subscription.sgml      |  2 +-
 src/backend/commands/subscriptioncmds.c       | 57 ++++++++++++++-----
 .../libpqwalreceiver/libpqwalreceiver.c       | 23 ++++++--
 src/include/replication/walreceiver.h         |  5 +-
 src/test/subscription/t/021_twophase.pl       | 41 ++++++++-----
 5 files changed, 91 insertions(+), 37 deletions(-)

diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index 0b23df1b77..475a42a2e3 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -70,7 +70,7 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
    <command>ALTER SUBSCRIPTION ... {SET|ADD|DROP} PUBLICATION ...</command>
    with <literal>refresh</literal> option as <literal>true</literal>,
    <command>ALTER SUBSCRIPTION ... SET (failover = true|false)</command> and
-   <command>ALTER SUBSCRIPTION ... SET (two_phase = true|false)</command>
+   <command>ALTER SUBSCRIPTION ... SET (two_phase = off)</command>
    cannot be executed inside a transaction block.
 
    These commands also cannot be executed when the subscription has
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index 61fd74c971..3944750ca8 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -1085,6 +1085,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 	Form_pg_subscription form;
 	bits32		supported_opts;
 	SubOpts		opts = {0};
+	bool		update_failover;
+	bool		update_two_phase;
 
 	rel = table_open(SubscriptionRelationId, RowExclusiveLock);
 
@@ -1155,12 +1157,6 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 								 errmsg("cannot set %s for enabled subscription",
 										"two_phase")));
 
-					if (!sub->slotname)
-						ereport(ERROR,
-								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-								 errmsg("cannot set %s for a subscription that does not have a slot name",
-										"two_phase")));
-
 					/*
 					 * Workers may still survive even if the subscription has
 					 * been disabled. They may read the pg_subscription
@@ -1187,10 +1183,33 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 								 errhint("Resolve these transactions and try again")));
 
 					/*
-					 * The changed two_phase option of the slot can't be
-					 * rolled back.
+					 * Altering the parameter from "true" to "false" within a
+					 * transaction is prohibited. Since the apply worker does
+					 * not alter the slot option to false, the backend must
+					 * connect to the publisher and expressly change the
+					 * parameter.
+					 *
+					 * There is no need to do something remarkable regarding
+					 * the "false" to "true" case; the backend process alters
+					 * subtwophase to LOGICALREP_TWOPHASE_STATE_PENDING once.
+					 * After the subscription is enabled, a new logical
+					 * replication worker requests to change the two_phase
+					 * option of its slot from pending to true when the
+					 * initial data synchronization is done. The code path is
+					 * the same as the case in which two_phase is initially
+					 * set to true.
 					 */
-					PreventInTransactionBlock(isTopLevel, "ALTER SUBSCRIPTION ... SET (two_phase)");
+					if (!opts.twophase)
+					{
+						if (!sub->slotname)
+							ereport(ERROR,
+									(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+									 errmsg("cannot set %s for a subscription that does not have a slot name",
+											"two_phase")));
+
+						PreventInTransactionBlock(isTopLevel,
+												  "ALTER SUBSCRIPTION ... SET (two_phase = false)");
+					}
 
 					/* Change system catalog acoordingly */
 					values[Anum_pg_subscription_subtwophasestate - 1] =
@@ -1548,14 +1567,24 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 	}
 
 	/*
-	 * Try to acquire the connection necessary for altering slot.
+	 * Check the need to alter the replication slot. Failover and two_phase
+	 * options are controlled by both the publisher (as a slot option) and the
+	 * subscriber (as a subscription option). The slot option must be altered
+	 * only when changing "true" to "false". The reason has already been
+	 * described in the ALTER_SUBSCRIPTION_OPTIONS section of this function.
+	 */
+	update_failover = replaces[Anum_pg_subscription_subfailover - 1];
+	update_two_phase = (replaces[Anum_pg_subscription_subtwophasestate - 1] &&
+						!opts.twophase);
+
+	/*
+	 * Try to acquire the connection necessary for altering slot, if needed.
 	 *
 	 * This has to be at the end because otherwise if there is an error while
 	 * doing the database operations we won't be able to rollback altered
 	 * slot.
 	 */
-	if (replaces[Anum_pg_subscription_subfailover - 1] ||
-		replaces[Anum_pg_subscription_subtwophasestate - 1])
+	if (update_failover || update_two_phase)
 	{
 		bool		must_use_password;
 		char	   *err;
@@ -1575,7 +1604,9 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 
 		PG_TRY();
 		{
-			walrcv_alter_slot(wrconn, sub->slotname, opts.failover, opts.twophase);
+			walrcv_alter_slot(wrconn, sub->slotname,
+							  update_failover ? &opts.failover : NULL,
+							  update_two_phase ? &opts.twophase : NULL);
 		}
 		PG_FINALLY();
 		{
diff --git a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
index 2f035a0c3c..07dfec947d 100644
--- a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
+++ b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
@@ -80,7 +80,7 @@ static char *libpqrcv_create_slot(WalReceiverConn *conn,
 								  CRSSnapshotAction snapshot_action,
 								  XLogRecPtr *lsn);
 static void libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-								bool failover, bool two_phase);
+								const bool *failover, const bool *two_phase);
 static pid_t libpqrcv_get_backend_pid(WalReceiverConn *conn);
 static WalRcvExecResult *libpqrcv_exec(WalReceiverConn *conn,
 									   const char *query,
@@ -1121,16 +1121,27 @@ libpqrcv_create_slot(WalReceiverConn *conn, const char *slotname,
  */
 static void
 libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-					bool failover, bool two_phase)
+					const bool *failover, const bool *two_phase)
 {
 	StringInfoData cmd;
 	PGresult   *res;
 
 	initStringInfo(&cmd);
-	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( FAILOVER %s, TWO_PHASE %s )",
-					 quote_identifier(slotname),
-					 failover ? "true" : "false",
-					 two_phase ? "true" : "false");
+	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( ",
+					 quote_identifier(slotname));
+
+	if (failover)
+		appendStringInfo(&cmd, "FAILOVER %s",
+						 *failover ? "true" : "false");
+
+	if (failover && two_phase)
+		appendStringInfo(&cmd, ", ");
+
+	if (two_phase)
+		appendStringInfo(&cmd, "TWO_PHASE %s",
+						 *two_phase ? "true" : "false");
+
+	appendStringInfoString(&cmd, " );");
 
 	res = libpqrcv_PQexec(conn->streamConn, cmd.data);
 	pfree(cmd.data);
diff --git a/src/include/replication/walreceiver.h b/src/include/replication/walreceiver.h
index 31fa1257ec..7ffa5a58b3 100644
--- a/src/include/replication/walreceiver.h
+++ b/src/include/replication/walreceiver.h
@@ -377,8 +377,9 @@ typedef char *(*walrcv_create_slot_fn) (WalReceiverConn *conn,
  */
 typedef void (*walrcv_alter_slot_fn) (WalReceiverConn *conn,
 									  const char *slotname,
-									  bool failover,
-									  bool two_phase);
+									  const bool *failover,
+									  const bool *two_phase);
+
 
 /*
  * walrcv_get_backend_pid_fn
diff --git a/src/test/subscription/t/021_twophase.pl b/src/test/subscription/t/021_twophase.pl
index 4e8f627f7b..f56dff4b12 100644
--- a/src/test/subscription/t/021_twophase.pl
+++ b/src/test/subscription/t/021_twophase.pl
@@ -375,6 +375,12 @@ $node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub");
 # then verify that the altered subscription reflects the two_phase option.
 ###############################
 
+# Confirm two-phase slot option is enabled before altering
+$result = $node_publisher->safe_psql('postgres',
+	"SELECT two_phase FROM pg_replication_slots WHERE slot_name = 'tap_sub_copy';"
+);
+is($result, qq(t), 'two-phase is enabled');
+
 # Alter subscription two_phase to false
 $node_subscriber->safe_psql('postgres',
     "ALTER SUBSCRIPTION tap_sub_copy DISABLE;");
@@ -393,7 +399,13 @@ $node_subscriber->wait_for_subscription_sync($node_publisher, $appname_copy);
 $result = $node_subscriber->safe_psql('postgres',
 	"SELECT subtwophasestate FROM pg_subscription WHERE subname = 'tap_sub_copy';"
 );
-is($result, qq(d), 'two-phase should be disabled');
+is($result, qq(d), 'two-phase subscription option should be disabled');
+
+# Make sure that the two-phase slot option is also disabled
+$result = $node_publisher->safe_psql('postgres',
+	"SELECT two_phase FROM pg_replication_slots WHERE slot_name = 'tap_sub_copy';"
+);
+is($result, qq(f), 'two-phase slot option should be disabled');
 
 # Now do a prepare on the publisher and make sure that it is not replicated.
 $node_publisher->safe_psql(
@@ -411,6 +423,19 @@ $result = $node_subscriber->safe_psql('postgres',
 	"SELECT count(*) FROM pg_prepared_xacts;");
 is($result, qq(0), 'should be no prepared transactions on subscriber');
 
+# Toggle the two_phase to "true" *before* the COMMIT PREPARED. Since we are the
+# special path for the case where both two_phase and failover are altered, it
+# is also set to "true".
+$node_subscriber->safe_psql('postgres',
+    "ALTER SUBSCRIPTION tap_sub_copy DISABLE;");
+$node_subscriber->poll_query_until('postgres',
+    "SELECT count(*) = 0 FROM pg_stat_activity WHERE backend_type = 'logical replication worker'"
+);
+$node_subscriber->safe_psql(
+	'postgres', "
+    ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = true, failover = true);
+    ALTER SUBSCRIPTION tap_sub_copy ENABLE;");
+
 # Now commit the insert and verify that it is replicated
 $node_publisher->safe_psql('postgres', "COMMIT PREPARED 'newgid';");
 
@@ -422,20 +447,6 @@ $result =
   $node_subscriber->safe_psql('postgres', "SELECT count(*) FROM tab_copy;");
 is($result, qq(3), 'replicated data in subscriber table');
 
-# Alter subscription two_phase to true
-$node_subscriber->safe_psql('postgres',
-    "ALTER SUBSCRIPTION tap_sub_copy DISABLE;");
-$node_subscriber->poll_query_until('postgres',
-    "SELECT count(*) = 0 FROM pg_stat_activity WHERE backend_type = 'logical replication worker'"
-);
-$node_subscriber->safe_psql(
-	'postgres', "
-    ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = true);
-    ALTER SUBSCRIPTION tap_sub_copy ENABLE;");
-
-# Wait for subscription startup
-$node_subscriber->wait_for_subscription_sync($node_publisher, $appname_copy);
-
 # Make sure that the two-phase is enabled on the subscriber
 $result = $node_subscriber->safe_psql('postgres',
 	"SELECT subtwophasestate FROM pg_subscription WHERE subname = 'tap_sub_copy';"
-- 
2.43.0

From 10a83945d53c1a83b8b6e555e10eb5b3fc2738d9 Mon Sep 17 00:00:00 2001
From: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Date: Mon, 8 Apr 2024 12:39:12 +0000
Subject: [PATCH v16 3/4] Abort prepared transactions while altering two_phase
 to off

If we alter the two_phase parameter from "on" to "off" and there are prepared
transactions on the subscriber, they won't be resolved. To avoid this issue, we
allow the backend to abort all prepared transactions while altering the
subscription.
---
 doc/src/sgml/ref/alter_subscription.sgml | 11 +++-
 src/backend/access/transam/twophase.c    | 17 +++---
 src/backend/commands/subscriptioncmds.c  | 73 +++++++++++++++---------
 src/include/access/twophase.h            |  3 +-
 src/test/subscription/t/021_twophase.pl  | 53 +++++++++++++++--
 5 files changed, 113 insertions(+), 44 deletions(-)

diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index 475a42a2e3..8801f37f0e 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -233,8 +233,6 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>, and
       <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>.
       Only a superuser can set <literal>password_required = false</literal>.
-      The <literal>two_phase</literal> parameter can only be altered when the
-      subscription is disabled.
      </para>
 
      <para>
@@ -256,6 +254,15 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>
       option is enabled.
      </para>
+
+     <para>
+      The <literal>two_phase</literal> parameter can only be altered when the
+      subscription is disabled. When altering the parameter from <literal>true</literal>
+      to <literal>false</literal>, the backend process checks for any incomplete
+      prepared transactions done by the logical replication worker (from when
+      <literal>two_phase</literal> parameter was still <literal>true</literal>)
+      and, if any are found, those are aborted.
+     </para>
     </listitem>
    </varlistentry>
 
diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index 35bce6809d..0be8a15367 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -2719,13 +2719,13 @@ IsTwoPhaseTransactionGidForSubid(Oid subid, char *gid)
 }
 
 /*
- * LookupGXactBySubid
- *		Check if the prepared transaction done by apply worker exists.
+ * GetGidListBySubid
+ *      Get a list of GIDs which is PREPARE'd by the given subscription.
  */
-bool
-LookupGXactBySubid(Oid subid)
+List *
+GetGidListBySubid(Oid subid)
 {
-	bool		found = false;
+	List	   *list = NIL;
 
 	LWLockAcquire(TwoPhaseStateLock, LW_SHARED);
 	for (int i = 0; i < TwoPhaseState->numPrepXacts; i++)
@@ -2735,11 +2735,8 @@ LookupGXactBySubid(Oid subid)
 		/* Ignore not-yet-valid GIDs. */
 		if (gxact->valid &&
 			IsTwoPhaseTransactionGidForSubid(subid, gxact->gid))
-		{
-			found = true;
-			break;
-		}
+			list = lappend(list, pstrdup(gxact->gid));
 	}
 	LWLockRelease(TwoPhaseStateLock);
-	return found;
+	return list;
 }
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index 3944750ca8..6e84628bd0 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -1171,44 +1171,63 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 								 errhint("Wait certain time and try again.")));
 
 					/*
-					 * two_phase cannot be disabled if there are any
-					 * uncommitted prepared transactions present.
-					 */
-					if (!opts.twophase &&
-						form->subtwophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
-						LookupGXactBySubid(subid))
-						ereport(ERROR,
-								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-								 errmsg("cannot disable two_phase when uncommitted prepared transactions present"),
-								 errhint("Resolve these transactions and try again")));
-
-					/*
-					 * Altering the parameter from "true" to "false" within a
-					 * transaction is prohibited. Since the apply worker does
-					 * not alter the slot option to false, the backend must
-					 * connect to the publisher and expressly change the
-					 * parameter.
-					 *
-					 * There is no need to do something remarkable regarding
-					 * the "false" to "true" case; the backend process alters
-					 * subtwophase to LOGICALREP_TWOPHASE_STATE_PENDING once.
-					 * After the subscription is enabled, a new logical
-					 * replication worker requests to change the two_phase
-					 * option of its slot from pending to true when the
-					 * initial data synchronization is done. The code path is
-					 * the same as the case in which two_phase is initially
-					 * set to true.
+					 * If two_phase was previously enabled, there is a
+					 * possibility that transactions have already been
+					 * PREPARE'd. They must be checked and rolled back.
 					 */
 					if (!opts.twophase)
 					{
+						List	   *prepared_xacts;
+
 						if (!sub->slotname)
 							ereport(ERROR,
 									(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
 									 errmsg("cannot set %s for a subscription that does not have a slot name",
 											"two_phase")));
 
+						/*
+						 * Altering the parameter from "true" to "false"
+						 * within a transaction is prohibited. Since the apply
+						 * worker does not alter the slot option to false, the
+						 * backend must connect to the publisher and expressly
+						 * change the parameter.
+						 *
+						 * There is no need to do something remarkable
+						 * regarding the "false" to "true" case; the backend
+						 * process alters subtwophase to
+						 * LOGICALREP_TWOPHASE_STATE_PENDING once. After the
+						 * subscription is enabled, a new logical replication
+						 * worker requests to change the two_phase option of
+						 * its slot from pending to true when the initial data
+						 * synchronization is done. The code path is the same
+						 * as the case in which two_phase is initially set to
+						 * true.
+						 */
 						PreventInTransactionBlock(isTopLevel,
 												  "ALTER SUBSCRIPTION ... SET (two_phase = false)");
+
+						/*
+						 * To prevent prepared transactions from being
+						 * isolated, they must manually be aborted.
+						 */
+						if (sub->twophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
+							(prepared_xacts = GetGidListBySubid(subid)) != NIL)
+						{
+							ereport(NOTICE,
+									(errmsg_plural("requested altering to %s but there is prepared transaction done by the subscription",
+												   "requested altering to %s but there are prepared transactions done by the subscription",
+												   list_length(prepared_xacts),
+												   "two_phase = false"),
+									 errdetail_plural("Such a transaction is being rollbacked.",
+													  "Such transactions are being rollbacked.",
+													  list_length(prepared_xacts))));
+
+							/* Abort all listed transactions */
+							foreach_ptr(char, gid, prepared_xacts)
+								FinishPreparedTransaction(gid, false);
+
+							list_free_deep(prepared_xacts);
+						}
 					}
 
 					/* Change system catalog acoordingly */
diff --git a/src/include/access/twophase.h b/src/include/access/twophase.h
index d37e06fdee..f7a5cf0c12 100644
--- a/src/include/access/twophase.h
+++ b/src/include/access/twophase.h
@@ -18,6 +18,7 @@
 #include "access/xlogdefs.h"
 #include "datatype/timestamp.h"
 #include "storage/lock.h"
+#include "nodes/pg_list.h"
 
 /*
  * GlobalTransactionData is defined in twophase.c; other places have no
@@ -65,6 +66,6 @@ extern bool LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 
 extern void TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid,
 								   int szgid);
-extern bool LookupGXactBySubid(Oid subid);
+extern List *GetGidListBySubid(Oid subid);
 
 #endif							/* TWOPHASE_H */
diff --git a/src/test/subscription/t/021_twophase.pl b/src/test/subscription/t/021_twophase.pl
index f56dff4b12..c3e15e537b 100644
--- a/src/test/subscription/t/021_twophase.pl
+++ b/src/test/subscription/t/021_twophase.pl
@@ -383,9 +383,9 @@ is($result, qq(t), 'two-phase is enabled');
 
 # Alter subscription two_phase to false
 $node_subscriber->safe_psql('postgres',
-    "ALTER SUBSCRIPTION tap_sub_copy DISABLE;");
+	"ALTER SUBSCRIPTION tap_sub_copy DISABLE;");
 $node_subscriber->poll_query_until('postgres',
-    "SELECT count(*) = 0 FROM pg_stat_activity WHERE backend_type = 'logical replication worker'"
+	"SELECT count(*) = 0 FROM pg_stat_activity WHERE backend_type = 'logical replication worker'"
 );
 $node_subscriber->safe_psql(
 	'postgres', "
@@ -427,9 +427,9 @@ is($result, qq(0), 'should be no prepared transactions on subscriber');
 # special path for the case where both two_phase and failover are altered, it
 # is also set to "true".
 $node_subscriber->safe_psql('postgres',
-    "ALTER SUBSCRIPTION tap_sub_copy DISABLE;");
+	"ALTER SUBSCRIPTION tap_sub_copy DISABLE;");
 $node_subscriber->poll_query_until('postgres',
-    "SELECT count(*) = 0 FROM pg_stat_activity WHERE backend_type = 'logical replication worker'"
+	"SELECT count(*) = 0 FROM pg_stat_activity WHERE backend_type = 'logical replication worker'"
 );
 $node_subscriber->safe_psql(
 	'postgres', "
@@ -453,6 +453,51 @@ $result = $node_subscriber->safe_psql('postgres',
 );
 is($result, qq(e), 'two-phase should be enabled');
 
+#####################
+# Check the case that prepared transactions exist on the subscriber node
+#####################
+
+# Prepare a transaction to insert some tuples into the table
+$node_publisher->safe_psql(
+	'postgres', "
+	BEGIN;
+	INSERT INTO tab_copy VALUES (101);
+	PREPARE TRANSACTION 'newgid';");
+
+$node_publisher->wait_for_catchup($appname_copy);
+
+# Verify the prepared transaction has been replicated to the subscriber because
+# two_phase is set to "true".
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT count(*) FROM pg_prepared_xacts;");
+is($result, q(1), "transaction has been prepared on subscriber");
+
+# Toggle the two_phase to "false" before the COMMIT PREPARED
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy DISABLE;");
+$node_subscriber->poll_query_until('postgres',
+	"SELECT count(*) = 0 FROM pg_stat_activity WHERE backend_type = 'logical replication worker'"
+);
+$node_subscriber->safe_psql(
+	'postgres', "
+    ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = false);
+    ALTER SUBSCRIPTION tap_sub_copy ENABLE;");
+
+# Verify any prepared transactions are aborted because two_phase is changed to
+# "false".
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT count(*) FROM pg_prepared_xacts;");
+is($result, q(0), "prepared transaction done by worker is aborted");
+
+# Do COMMIT PREPARED the prepared transaction
+$node_publisher->safe_psql('postgres', "COMMIT PREPARED 'newgid';");
+$node_publisher->wait_for_catchup($appname_copy);
+
+# Verify inserted tuples are replicated
+$result =
+  $node_subscriber->safe_psql('postgres', "SELECT count(*) FROM tab_copy;");
+is($result, q(4), "prepared transactions on publisher can be replicated");
+
 $node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub_copy;");
 $node_publisher->safe_psql('postgres', "DROP PUBLICATION tap_pub_copy;");
 
-- 
2.43.0

From f6f28783ba1783d9fc523a5ce462302e9bd5150c Mon Sep 17 00:00:00 2001
From: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Date: Fri, 19 Apr 2024 11:03:19 +0000
Subject: [PATCH v16 4/4] Add force_alter option for ALTER SUBSCRIPTION ... SET
 command

Previously, all prepared transactions on the standby were rolled back when
toggling two_phase from "true" to "false". However, this operation may not be
expected by users. To ensure users understand what happens, we added the
"force_alter" parameter. When two_phase is toggling to "false", and there are
prepared transactions, they will be aborted only when "force_alter" is set to
true. Otherwise, an ERROR occurs.
---
 doc/src/sgml/catalogs.sgml                 |  12 ++
 doc/src/sgml/ref/alter_subscription.sgml   |  16 ++-
 doc/src/sgml/ref/create_subscription.sgml  |  24 ++++
 src/backend/catalog/pg_subscription.c      |   1 +
 src/backend/catalog/system_views.sql       |   2 +-
 src/backend/commands/subscriptioncmds.c    |  36 ++++-
 src/bin/pg_dump/pg_dump.c                  |  18 ++-
 src/bin/pg_dump/pg_dump.h                  |   1 +
 src/bin/psql/describe.c                    |   7 +-
 src/include/catalog/pg_subscription.h      |  13 ++
 src/test/regress/expected/subscription.out | 152 ++++++++++-----------
 src/test/subscription/t/021_twophase.pl    |  25 +++-
 12 files changed, 216 insertions(+), 91 deletions(-)

diff --git a/doc/src/sgml/catalogs.sgml b/doc/src/sgml/catalogs.sgml
index b654fae1b2..bca2f0c77a 100644
--- a/doc/src/sgml/catalogs.sgml
+++ b/doc/src/sgml/catalogs.sgml
@@ -8035,6 +8035,18 @@ SCRAM-SHA-256$<replaceable>&lt;iteration count&gt;</replaceable>:<replaceable>&l
       </para></entry>
      </row>
 
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>subforcealter</structfield> <type>bool</type>
+      </para>
+      <para>
+       If true, then the <link linkend="sql-altersubscription"><command>ALTER SUBSCRIPTION</command></link>
+       can sometimes be forced to proceed instead of giving an error. See
+       <link linkend="sql-createsubscription-params-with-force-alter"><literal>force_alter</literal></link>
+       parameter for details about when this might be useful.
+      </para></entry>
+     </row>
+
      <row>
       <entry role="catalog_table_entry"><para role="column_definition">
        <structfield>subconninfo</structfield> <type>text</type>
diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index 8801f37f0e..ab2cdaeaa3 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -230,8 +230,9 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-password-required"><literal>password_required</literal></link>,
       <link linkend="sql-createsubscription-params-with-run-as-owner"><literal>run_as_owner</literal></link>,
       <link linkend="sql-createsubscription-params-with-origin"><literal>origin</literal></link>,
-      <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>, and
-      <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>.
+      <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>,
+      <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>, and
+      <link linkend="sql-createsubscription-params-with-force-alter"><literal>force_alter</literal></link>
       Only a superuser can set <literal>password_required = false</literal>.
      </para>
 
@@ -257,11 +258,12 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
 
      <para>
       The <literal>two_phase</literal> parameter can only be altered when the
-      subscription is disabled. When altering the parameter from <literal>true</literal>
-      to <literal>false</literal>, the backend process checks for any incomplete
-      prepared transactions done by the logical replication worker (from when
-      <literal>two_phase</literal> parameter was still <literal>true</literal>)
-      and, if any are found, those are aborted.
+      subscription is disabled. Altering the parameter from <literal>true</literal>
+      to <literal>false</literal> will give an error when there are prepared
+      transactions done by the logical replication worker. If you want to alter
+      the parameter forcibly in this case,
+      <link linkend="sql-createsubscription-params-with-force-alter"><literal>force_alter</literal></link>
+      option must be set to <literal>true</literal>.
      </para>
     </listitem>
    </varlistentry>
diff --git a/doc/src/sgml/ref/create_subscription.sgml b/doc/src/sgml/ref/create_subscription.sgml
index 740b7d9421..83ac52f865 100644
--- a/doc/src/sgml/ref/create_subscription.sgml
+++ b/doc/src/sgml/ref/create_subscription.sgml
@@ -428,6 +428,30 @@ CREATE SUBSCRIPTION <replaceable class="parameter">subscription_name</replaceabl
          </para>
         </listitem>
        </varlistentry>
+
+       <varlistentry id="sql-createsubscription-params-with-force-alter">
+        <term><literal>force_alter</literal> (<type>boolean</type>)</term>
+        <listitem>
+         <para>
+          Specifies if the <link linkend="sql-altersubscription"><command>ALTER SUBSCRIPTION</command></link>
+          can be forced to proceed instead of giving an error.
+         </para>
+         <para>
+          There is currently only one scenario where this parameter has any
+          effect: When altering <literal>two_phase</literal> option from
+          <literal>true</literal> to <literal>false</literal> it is possible
+          for there to be incomplete prepared transactions done by the logical
+          replication worker (from when <literal>two_phase</literal> parameter
+          was still <literal>true</literal>). If <literal>force_alter</literal>
+          is <literal>false</literal>, then this will give an error; if
+          <literal>force_alter</literal> is <literal>true</literal>, then the
+          incomplete prepared transactions are aborted and the alter will proceed.
+         </para>
+         <para>
+          The default is <literal>false</literal>.
+         </para>
+        </listitem>
+       </varlistentry>
       </variablelist></para>
 
     </listitem>
diff --git a/src/backend/catalog/pg_subscription.c b/src/backend/catalog/pg_subscription.c
index 9efc9159f2..b568fe3470 100644
--- a/src/backend/catalog/pg_subscription.c
+++ b/src/backend/catalog/pg_subscription.c
@@ -72,6 +72,7 @@ GetSubscription(Oid subid, bool missing_ok)
 	sub->passwordrequired = subform->subpasswordrequired;
 	sub->runasowner = subform->subrunasowner;
 	sub->failover = subform->subfailover;
+	sub->forcealter = subform->subforcealter;
 
 	/* Get conninfo */
 	datum = SysCacheGetAttrNotNull(SUBSCRIPTIONOID,
diff --git a/src/backend/catalog/system_views.sql b/src/backend/catalog/system_views.sql
index 19cabc9a47..b89eacc96b 100644
--- a/src/backend/catalog/system_views.sql
+++ b/src/backend/catalog/system_views.sql
@@ -1355,7 +1355,7 @@ REVOKE ALL ON pg_replication_origin_status FROM public;
 REVOKE ALL ON pg_subscription FROM public;
 GRANT SELECT (oid, subdbid, subskiplsn, subname, subowner, subenabled,
               subbinary, substream, subtwophasestate, subdisableonerr,
-			  subpasswordrequired, subrunasowner, subfailover,
+			  subpasswordrequired, subrunasowner, subfailover, subforcealter,
               subslotname, subsynccommit, subpublications, suborigin)
     ON pg_subscription TO public;
 
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index 6e84628bd0..ed95b858ee 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -73,6 +73,7 @@
 #define SUBOPT_FAILOVER				0x00002000
 #define SUBOPT_LSN					0x00004000
 #define SUBOPT_ORIGIN				0x00008000
+#define SUBOPT_FORCE_ALTER			0x00010000
 
 /* check if the 'val' has 'bits' set */
 #define IsSet(val, bits)  (((val) & (bits)) == (bits))
@@ -100,6 +101,7 @@ typedef struct SubOpts
 	bool		failover;
 	char	   *origin;
 	XLogRecPtr	lsn;
+	bool		force_alter;
 } SubOpts;
 
 static List *fetch_table_list(WalReceiverConn *wrconn, List *publications);
@@ -162,6 +164,8 @@ parse_subscription_options(ParseState *pstate, List *stmt_options,
 		opts->failover = false;
 	if (IsSet(supported_opts, SUBOPT_ORIGIN))
 		opts->origin = pstrdup(LOGICALREP_ORIGIN_ANY);
+	if (IsSet(supported_opts, SUBOPT_FORCE_ALTER))
+		opts->force_alter = false;
 
 	/* Parse options */
 	foreach(lc, stmt_options)
@@ -355,6 +359,15 @@ parse_subscription_options(ParseState *pstate, List *stmt_options,
 			opts->specified_opts |= SUBOPT_LSN;
 			opts->lsn = lsn;
 		}
+		else if (IsSet(supported_opts, SUBOPT_FORCE_ALTER) &&
+				 strcmp(defel->defname, "force_alter") == 0)
+		{
+			if (IsSet(opts->specified_opts, SUBOPT_FORCE_ALTER))
+				errorConflictingDefElem(defel, pstate);
+
+			opts->specified_opts |= SUBOPT_FORCE_ALTER;
+			opts->force_alter = defGetBoolean(defel);
+		}
 		else
 			ereport(ERROR,
 					(errcode(ERRCODE_SYNTAX_ERROR),
@@ -592,7 +605,8 @@ CreateSubscription(ParseState *pstate, CreateSubscriptionStmt *stmt,
 					  SUBOPT_SYNCHRONOUS_COMMIT | SUBOPT_BINARY |
 					  SUBOPT_STREAMING | SUBOPT_TWOPHASE_COMMIT |
 					  SUBOPT_DISABLE_ON_ERR | SUBOPT_PASSWORD_REQUIRED |
-					  SUBOPT_RUN_AS_OWNER | SUBOPT_FAILOVER | SUBOPT_ORIGIN);
+					  SUBOPT_RUN_AS_OWNER | SUBOPT_FAILOVER | SUBOPT_ORIGIN |
+					  SUBOPT_FORCE_ALTER);
 	parse_subscription_options(pstate, stmt->options, supported_opts, &opts);
 
 	/*
@@ -699,6 +713,7 @@ CreateSubscription(ParseState *pstate, CreateSubscriptionStmt *stmt,
 	values[Anum_pg_subscription_subpasswordrequired - 1] = BoolGetDatum(opts.passwordrequired);
 	values[Anum_pg_subscription_subrunasowner - 1] = BoolGetDatum(opts.runasowner);
 	values[Anum_pg_subscription_subfailover - 1] = BoolGetDatum(opts.failover);
+	values[Anum_pg_subscription_subforcealter - 1] = BoolGetDatum(opts.force_alter);
 	values[Anum_pg_subscription_subconninfo - 1] =
 		CStringGetTextDatum(conninfo);
 	if (opts.slot_name)
@@ -1138,7 +1153,7 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 								  SUBOPT_DISABLE_ON_ERR |
 								  SUBOPT_PASSWORD_REQUIRED |
 								  SUBOPT_RUN_AS_OWNER | SUBOPT_FAILOVER |
-								  SUBOPT_ORIGIN);
+								  SUBOPT_ORIGIN | SUBOPT_FORCE_ALTER);
 
 				parse_subscription_options(pstate, stmt->options,
 										   supported_opts, &opts);
@@ -1213,6 +1228,23 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 						if (sub->twophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
 							(prepared_xacts = GetGidListBySubid(subid)) != NIL)
 						{
+							bool		raise_error =
+								IsSet(opts.specified_opts, SUBOPT_FORCE_ALTER) ?
+								!opts.force_alter : !sub->forcealter;
+
+							/*
+							 * Abort prepared transactions only if
+							 * 'force_alter' option is true. Otherwise raise
+							 * an ERROR.
+							 */
+							if (raise_error)
+								ereport(ERROR,
+										(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+										 errmsg("cannot alter %s when there are prepared transactions",
+												"two_phase = false"),
+										 errhint("Resolve these transactions or set %s, and then try again.",
+												 "force_alter = true")));
+
 							ereport(NOTICE,
 									(errmsg_plural("requested altering to %s but there is prepared transaction done by the subscription",
 												   "requested altering to %s but there are prepared transactions done by the subscription",
diff --git a/src/bin/pg_dump/pg_dump.c b/src/bin/pg_dump/pg_dump.c
index 5426f1177c..85c69a835b 100644
--- a/src/bin/pg_dump/pg_dump.c
+++ b/src/bin/pg_dump/pg_dump.c
@@ -4754,6 +4754,7 @@ getSubscriptions(Archive *fout)
 	int			i_suboriginremotelsn;
 	int			i_subenabled;
 	int			i_subfailover;
+	int			i_subforcealter;
 	int			i,
 				ntups;
 
@@ -4826,10 +4827,17 @@ getSubscriptions(Archive *fout)
 
 	if (fout->remoteVersion >= 170000)
 		appendPQExpBufferStr(query,
-							 " s.subfailover\n");
+							 " s.subfailover,\n");
 	else
 		appendPQExpBuffer(query,
-						  " false AS subfailover\n");
+						  " false AS subfailover,\n");
+
+	if (fout->remoteVersion >= 170000)
+		appendPQExpBufferStr(query,
+							 " s.subforcealter\n");
+	else
+		appendPQExpBuffer(query,
+						  " false AS subforcealter\n");
 
 	appendPQExpBufferStr(query,
 						 "FROM pg_subscription s\n");
@@ -4869,6 +4877,7 @@ getSubscriptions(Archive *fout)
 	i_suboriginremotelsn = PQfnumber(res, "suboriginremotelsn");
 	i_subenabled = PQfnumber(res, "subenabled");
 	i_subfailover = PQfnumber(res, "subfailover");
+	i_subforcealter = PQfnumber(res, "subforcealter");
 
 	subinfo = pg_malloc(ntups * sizeof(SubscriptionInfo));
 
@@ -4915,6 +4924,8 @@ getSubscriptions(Archive *fout)
 			pg_strdup(PQgetvalue(res, i, i_subenabled));
 		subinfo[i].subfailover =
 			pg_strdup(PQgetvalue(res, i, i_subfailover));
+		subinfo[i].subforcealter =
+			pg_strdup(PQgetvalue(res, i, i_subforcealter));
 
 		/* Decide whether we want to dump it */
 		selectDumpableObject(&(subinfo[i].dobj), fout);
@@ -5155,6 +5166,9 @@ dumpSubscription(Archive *fout, const SubscriptionInfo *subinfo)
 	if (strcmp(subinfo->subfailover, "t") == 0)
 		appendPQExpBufferStr(query, ", failover = true");
 
+	if (strcmp(subinfo->subforcealter, "t") == 0)
+		appendPQExpBufferStr(query, ", force_alter = true");
+
 	if (strcmp(subinfo->subsynccommit, "off") != 0)
 		appendPQExpBuffer(query, ", synchronous_commit = %s", fmtId(subinfo->subsynccommit));
 
diff --git a/src/bin/pg_dump/pg_dump.h b/src/bin/pg_dump/pg_dump.h
index 4b2e5870a9..8f5f9d13b9 100644
--- a/src/bin/pg_dump/pg_dump.h
+++ b/src/bin/pg_dump/pg_dump.h
@@ -671,6 +671,7 @@ typedef struct _SubscriptionInfo
 	char	   *suborigin;
 	char	   *suboriginremotelsn;
 	char	   *subfailover;
+	char	   *subforcealter;
 } SubscriptionInfo;
 
 /*
diff --git a/src/bin/psql/describe.c b/src/bin/psql/describe.c
index 7c9a1f234c..abf91a81fa 100644
--- a/src/bin/psql/describe.c
+++ b/src/bin/psql/describe.c
@@ -6539,7 +6539,7 @@ describeSubscriptions(const char *pattern, bool verbose)
 	printQueryOpt myopt = pset.popt;
 	static const bool translate_columns[] = {false, false, false, false,
 		false, false, false, false, false, false, false, false, false, false,
-	false};
+	false, false};
 
 	if (pset.sversion < 100000)
 	{
@@ -6608,6 +6608,11 @@ describeSubscriptions(const char *pattern, bool verbose)
 							  ", subfailover AS \"%s\"\n",
 							  gettext_noop("Failover"));
 
+		if (pset.sversion >= 170000)
+			appendPQExpBuffer(&buf,
+							  ", subforcealter AS \"%s\"\n",
+							  gettext_noop("Force alter"));
+
 		appendPQExpBuffer(&buf,
 						  ",  subsynccommit AS \"%s\"\n"
 						  ",  subconninfo AS \"%s\"\n",
diff --git a/src/include/catalog/pg_subscription.h b/src/include/catalog/pg_subscription.h
index 0aa14ec4a2..deac7aa943 100644
--- a/src/include/catalog/pg_subscription.h
+++ b/src/include/catalog/pg_subscription.h
@@ -98,6 +98,13 @@ CATALOG(pg_subscription,6100,SubscriptionRelationId) BKI_SHARED_RELATION BKI_ROW
 								 * slots) in the upstream database are enabled
 								 * to be synchronized to the standbys. */
 
+	bool		subforcealter;	/* True allows the ALTER SUBSCRIPTION command
+								 * to proceed under conditions that would
+								 * otherwise result in an error. Currently,
+								 * 'force_alter' only has an effect when
+								 * altering the two_phase option from "true"
+								 * to "false". */
+
 #ifdef CATALOG_VARLEN			/* variable-length fields start here */
 	/* Connection string to the publisher */
 	text		subconninfo BKI_FORCE_NOT_NULL;
@@ -151,6 +158,12 @@ typedef struct Subscription
 								 * (i.e. the main slot and the table sync
 								 * slots) in the upstream database are enabled
 								 * to be synchronized to the standbys. */
+	bool		forcealter;		/* True allows the ALTER SUBSCRIPTION command
+								 * to proceed under conditions that would
+								 * otherwise result in an error. Currently,
+								 * 'force_alter' only has an effect when
+								 * altering the two_phase option from "true"
+								 * to "false". */
 	char	   *conninfo;		/* Connection string to the publisher */
 	char	   *slotname;		/* Name of the replication slot */
 	char	   *synccommit;		/* Synchronous commit setting for worker */
diff --git a/src/test/regress/expected/subscription.out b/src/test/regress/expected/subscription.out
index 51fa4b9690..b36fc6b8f7 100644
--- a/src/test/regress/expected/subscription.out
+++ b/src/test/regress/expected/subscription.out
@@ -116,18 +116,18 @@ CREATE SUBSCRIPTION regress_testsub4 CONNECTION 'dbname=regress_doesnotexist' PU
 WARNING:  subscription was created, but is not connected
 HINT:  To initiate replication, you must manually create the replication slot, enable the subscription, and refresh the subscription.
 \dRs+ regress_testsub4
-                                                                                                                 List of subscriptions
-       Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
-------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub4 | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | none   | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                        List of subscriptions
+       Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub4 | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | none   | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub4 SET (origin = any);
 \dRs+ regress_testsub4
-                                                                                                                 List of subscriptions
-       Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
-------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub4 | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                        List of subscriptions
+       Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub4 | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 DROP SUBSCRIPTION regress_testsub3;
@@ -145,10 +145,10 @@ ALTER SUBSCRIPTION regress_testsub CONNECTION 'foobar';
 ERROR:  invalid connection string syntax: missing "=" after "foobar" in connection info string
 
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET PUBLICATION testpub2, testpub3 WITH (refresh = false);
@@ -157,10 +157,10 @@ ALTER SUBSCRIPTION regress_testsub SET (slot_name = 'newname');
 ALTER SUBSCRIPTION regress_testsub SET (password_required = false);
 ALTER SUBSCRIPTION regress_testsub SET (run_as_owner = true);
 \dRs+
-                                                                                                                     List of subscriptions
-      Name       |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |           Conninfo           | Skip LSN 
------------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+------------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | f                 | t             | f        | off                | dbname=regress_doesnotexist2 | 0/0
+                                                                                                                            List of subscriptions
+      Name       |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |           Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+------------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | f                 | t             | f        | f           | off                | dbname=regress_doesnotexist2 | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (password_required = true);
@@ -176,10 +176,10 @@ ERROR:  unrecognized subscription parameter: "create_slot"
 -- ok
 ALTER SUBSCRIPTION regress_testsub SKIP (lsn = '0/12345');
 \dRs+
-                                                                                                                     List of subscriptions
-      Name       |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |           Conninfo           | Skip LSN 
------------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+------------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist2 | 0/12345
+                                                                                                                            List of subscriptions
+      Name       |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |           Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+------------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist2 | 0/12345
 (1 row)
 
 -- ok - with lsn = NONE
@@ -188,10 +188,10 @@ ALTER SUBSCRIPTION regress_testsub SKIP (lsn = NONE);
 ALTER SUBSCRIPTION regress_testsub SKIP (lsn = '0/0');
 ERROR:  invalid WAL location (LSN): 0/0
 \dRs+
-                                                                                                                     List of subscriptions
-      Name       |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |           Conninfo           | Skip LSN 
------------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+------------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist2 | 0/0
+                                                                                                                            List of subscriptions
+      Name       |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |           Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+------------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist2 | 0/0
 (1 row)
 
 BEGIN;
@@ -223,10 +223,10 @@ ALTER SUBSCRIPTION regress_testsub_foo SET (synchronous_commit = foobar);
 ERROR:  invalid value for parameter "synchronous_commit": "foobar"
 HINT:  Available values: local, remote_write, remote_apply, on, off.
 \dRs+
-                                                                                                                       List of subscriptions
-        Name         |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |           Conninfo           | Skip LSN 
----------------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+------------------------------+----------
- regress_testsub_foo | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | t                 | f             | f        | local              | dbname=regress_doesnotexist2 | 0/0
+                                                                                                                              List of subscriptions
+        Name         |           Owner           | Enabled |     Publication     | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |           Conninfo           | Skip LSN 
+---------------------+---------------------------+---------+---------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+------------------------------+----------
+ regress_testsub_foo | regress_subscription_user | f       | {testpub2,testpub3} | f      | off       | d                | f                | any    | t                 | f             | f        | f           | local              | dbname=regress_doesnotexist2 | 0/0
 (1 row)
 
 -- rename back to keep the rest simple
@@ -255,19 +255,19 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 WARNING:  subscription was created, but is not connected
 HINT:  To initiate replication, you must manually create the replication slot, enable the subscription, and refresh the subscription.
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | t      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | t      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (binary = false);
 ALTER SUBSCRIPTION regress_testsub SET (slot_name = NONE);
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 DROP SUBSCRIPTION regress_testsub;
@@ -279,27 +279,27 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 WARNING:  subscription was created, but is not connected
 HINT:  To initiate replication, you must manually create the replication slot, enable the subscription, and refresh the subscription.
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | on        | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | on        | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (streaming = parallel);
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | parallel  | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | parallel  | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (streaming = false);
 ALTER SUBSCRIPTION regress_testsub SET (slot_name = NONE);
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 -- fail - publication already exists
@@ -314,10 +314,10 @@ ALTER SUBSCRIPTION regress_testsub ADD PUBLICATION testpub1, testpub2 WITH (refr
 ALTER SUBSCRIPTION regress_testsub ADD PUBLICATION testpub1, testpub2 WITH (refresh = false);
 ERROR:  publication "testpub1" is already in subscription "regress_testsub"
 \dRs+
-                                                                                                                        List of subscriptions
-      Name       |           Owner           | Enabled |         Publication         | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-----------------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub,testpub1,testpub2} | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                               List of subscriptions
+      Name       |           Owner           | Enabled |         Publication         | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-----------------------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub,testpub1,testpub2} | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 -- fail - publication used more than once
@@ -332,10 +332,10 @@ ERROR:  publication "testpub3" is not in subscription "regress_testsub"
 -- ok - delete publications
 ALTER SUBSCRIPTION regress_testsub DROP PUBLICATION testpub1, testpub2 WITH (refresh = false);
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 DROP SUBSCRIPTION regress_testsub;
@@ -371,19 +371,19 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 WARNING:  subscription was created, but is not connected
 HINT:  To initiate replication, you must manually create the replication slot, enable the subscription, and refresh the subscription.
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | p                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | p                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 -- We can alter streaming when two_phase enabled
 ALTER SUBSCRIPTION regress_testsub SET (streaming = true);
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | on        | p                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | on        | p                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (slot_name = NONE);
@@ -393,10 +393,10 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 WARNING:  subscription was created, but is not connected
 HINT:  To initiate replication, you must manually create the replication slot, enable the subscription, and refresh the subscription.
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | on        | p                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | on        | p                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (slot_name = NONE);
@@ -409,18 +409,18 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 WARNING:  subscription was created, but is not connected
 HINT:  To initiate replication, you must manually create the replication slot, enable the subscription, and refresh the subscription.
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | f                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (disable_on_error = true);
 \dRs+
-                                                                                                                List of subscriptions
-      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Synchronous commit |          Conninfo           | Skip LSN 
------------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------------------+-----------------------------+----------
- regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | t                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
+                                                                                                                       List of subscriptions
+      Name       |           Owner           | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Force alter | Synchronous commit |          Conninfo           | Skip LSN 
+-----------------+---------------------------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+-------------+--------------------+-----------------------------+----------
+ regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | d                | t                | any    | t                 | f             | f        | f           | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
 ALTER SUBSCRIPTION regress_testsub SET (slot_name = NONE);
diff --git a/src/test/subscription/t/021_twophase.pl b/src/test/subscription/t/021_twophase.pl
index c3e15e537b..d58b046571 100644
--- a/src/test/subscription/t/021_twophase.pl
+++ b/src/test/subscription/t/021_twophase.pl
@@ -472,15 +472,36 @@ $result = $node_subscriber->safe_psql('postgres',
 	"SELECT count(*) FROM pg_prepared_xacts;");
 is($result, q(1), "transaction has been prepared on subscriber");
 
-# Toggle the two_phase to "false" before the COMMIT PREPARED
+# Disable the subscription to alter the two_phase option
 $node_subscriber->safe_psql('postgres',
 	"ALTER SUBSCRIPTION tap_sub_copy DISABLE;");
 $node_subscriber->poll_query_until('postgres',
 	"SELECT count(*) = 0 FROM pg_stat_activity WHERE backend_type = 'logical replication worker'"
 );
+
+# Try altering the two_phase option to "false". The command will fail since
+# there is a prepared transaction and the 'force_alter' option is not specified
+# as true.
+
+my $stdout;
+my $stderr;
+
+($result, $stdout, $stderr) = $node_subscriber->psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = false);");
+ok( $stderr =~
+	  /cannot alter two_phase = false when there are prepared transactions/,
+	'ALTER SUBSCRIPTION failed');
+
+# Verify the prepared transaction still exists
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT count(*) FROM pg_prepared_xacts;");
+is($result, q(1), "prepared transaction still exists");
+
+# Alter the two_phase true to false with the force_alter option enabled. This
+# command will succeed after aborting the prepared transaction.
 $node_subscriber->safe_psql(
 	'postgres', "
-    ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = false);
+	ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = false, force_alter = true);
     ALTER SUBSCRIPTION tap_sub_copy ENABLE;");
 
 # Verify any prepared transactions are aborted because two_phase is changed to
-- 
2.43.0

From 0006608c5b65941f43c5ce622f64144f2030adff Mon Sep 17 00:00:00 2001
From: Ajin Cherian <ajinc@fast.au.fujitsu.com>
Date: Fri, 5 Apr 2024 06:47:18 -0400
Subject: [PATCH v17 1/3] Allow altering of two_phase option of a SUBSCRIPTION

This patch allows the user to alter the 'two_phase' option of a subscriber provided no
uncommitted prepared transactions are pending on that subscription.

Author: Cherian Ajin, Hayato Kuroda
---
 doc/src/sgml/ref/alter_subscription.sgml      |  12 +-
 src/backend/access/transam/twophase.c         |  62 ++++++++
 src/backend/commands/subscriptioncmds.c       | 135 +++++++++++++-----
 .../libpqwalreceiver/libpqwalreceiver.c       |   9 +-
 src/backend/replication/logical/launcher.c    |  12 +-
 src/backend/replication/logical/worker.c      |  25 +---
 src/backend/replication/slot.c                |  18 ++-
 src/backend/replication/walsender.c           |  18 ++-
 src/bin/psql/tab-complete.c                   |   2 +-
 src/include/access/twophase.h                 |   5 +
 src/include/replication/slot.h                |   3 +-
 src/include/replication/walreceiver.h         |  11 +-
 src/include/replication/worker_internal.h     |   3 +-
 src/test/regress/expected/subscription.out    |   5 +-
 src/test/regress/sql/subscription.sql         |   5 +-
 src/test/subscription/t/021_twophase.pl       |  77 +++++++++-
 16 files changed, 308 insertions(+), 94 deletions(-)

diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index 476f195622..0b23df1b77 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -68,8 +68,9 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
   <para>
    Commands <command>ALTER SUBSCRIPTION ... REFRESH PUBLICATION</command>,
    <command>ALTER SUBSCRIPTION ... {SET|ADD|DROP} PUBLICATION ...</command>
-   with <literal>refresh</literal> option as <literal>true</literal> and
-   <command>ALTER SUBSCRIPTION ... SET (failover = true|false)</command>
+   with <literal>refresh</literal> option as <literal>true</literal>,
+   <command>ALTER SUBSCRIPTION ... SET (failover = true|false)</command> and
+   <command>ALTER SUBSCRIPTION ... SET (two_phase = true|false)</command>
    cannot be executed inside a transaction block.
 
    These commands also cannot be executed when the subscription has
@@ -228,9 +229,12 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-disable-on-error"><literal>disable_on_error</literal></link>,
       <link linkend="sql-createsubscription-params-with-password-required"><literal>password_required</literal></link>,
       <link linkend="sql-createsubscription-params-with-run-as-owner"><literal>run_as_owner</literal></link>,
-      <link linkend="sql-createsubscription-params-with-origin"><literal>origin</literal></link>, and
-      <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>.
+      <link linkend="sql-createsubscription-params-with-origin"><literal>origin</literal></link>,
+      <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>, and
+      <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>.
       Only a superuser can set <literal>password_required = false</literal>.
+      The <literal>two_phase</literal> parameter can only be altered when the
+      subscription is disabled.
      </para>
 
      <para>
diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index 9a8257fcaf..35bce6809d 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -2681,3 +2681,65 @@ LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 	LWLockRelease(TwoPhaseStateLock);
 	return found;
 }
+
+/*
+ * TwoPhaseTransactionGid
+ *		Form the prepared transaction GID for two_phase transactions.
+ *
+ * Return the GID in the supplied buffer.
+ */
+void
+TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid, int szgid)
+{
+	Assert(subid != InvalidRepOriginId);
+
+	if (!TransactionIdIsValid(xid))
+		ereport(ERROR,
+				(errcode(ERRCODE_PROTOCOL_VIOLATION),
+				 errmsg_internal("invalid two-phase transaction ID")));
+
+	snprintf(gid, szgid, "pg_gid_%u_%u", subid, xid);
+}
+
+/*
+ * IsTwoPhaseTransactionGidForSubid
+ *		Check whether the given GID (as formed by TwoPhaseTransactionGid) is
+ *		for the specified 'subid'.
+ */
+static bool
+IsTwoPhaseTransactionGidForSubid(Oid subid, char *gid)
+{
+	int			ret;
+	Oid			subid_written;
+	TransactionId xid;
+
+	ret = sscanf(gid, "pg_gid_%u_%u", &subid_written, &xid);
+
+	return (ret == 2 && subid == subid_written);
+}
+
+/*
+ * LookupGXactBySubid
+ *		Check if the prepared transaction done by apply worker exists.
+ */
+bool
+LookupGXactBySubid(Oid subid)
+{
+	bool		found = false;
+
+	LWLockAcquire(TwoPhaseStateLock, LW_SHARED);
+	for (int i = 0; i < TwoPhaseState->numPrepXacts; i++)
+	{
+		GlobalTransaction gxact = TwoPhaseState->prepXacts[i];
+
+		/* Ignore not-yet-valid GIDs. */
+		if (gxact->valid &&
+			IsTwoPhaseTransactionGidForSubid(subid, gxact->gid))
+		{
+			found = true;
+			break;
+		}
+	}
+	LWLockRelease(TwoPhaseStateLock);
+	return found;
+}
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index e407428dbc..255628c396 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -16,6 +16,7 @@
 
 #include "access/htup_details.h"
 #include "access/table.h"
+#include "access/twophase.h"
 #include "access/xact.h"
 #include "catalog/catalog.h"
 #include "catalog/dependency.h"
@@ -109,6 +110,9 @@ static void check_publications_origin(WalReceiverConn *wrconn,
 static void check_duplicates_in_publist(List *publist, Datum *datums);
 static List *merge_publications(List *oldpublist, List *newpublist, bool addpub, const char *subname);
 static void ReportSlotConnectionError(List *rstates, Oid subid, char *slotname, char *err);
+static void CommonChecksForFailoverAndTwophase(Subscription *sub,
+											   const char *option,
+											   bool isTopLevel);
 
 
 /*
@@ -259,21 +263,9 @@ parse_subscription_options(ParseState *pstate, List *stmt_options,
 			opts->specified_opts |= SUBOPT_STREAMING;
 			opts->streaming = defGetStreamingMode(defel);
 		}
-		else if (strcmp(defel->defname, "two_phase") == 0)
+		else if (IsSet(supported_opts, SUBOPT_TWOPHASE_COMMIT) &&
+				 strcmp(defel->defname, "two_phase") == 0)
 		{
-			/*
-			 * Do not allow toggling of two_phase option. Doing so could cause
-			 * missing of transactions and lead to an inconsistent replica.
-			 * See comments atop worker.c
-			 *
-			 * Note: Unsupported twophase indicates that this call originated
-			 * from AlterSubscription.
-			 */
-			if (!IsSet(supported_opts, SUBOPT_TWOPHASE_COMMIT))
-				ereport(ERROR,
-						(errcode(ERRCODE_SYNTAX_ERROR),
-						 errmsg("unrecognized subscription parameter: \"%s\"", defel->defname)));
-
 			if (IsSet(opts->specified_opts, SUBOPT_TWOPHASE_COMMIT))
 				errorConflictingDefElem(defel, pstate);
 
@@ -1077,6 +1069,45 @@ AlterSubscription_refresh(Subscription *sub, bool copy_data,
 		table_close(rel, NoLock);
 }
 
+/*
+ * Common checks for altering failover and two_phase option
+ */
+static void
+CommonChecksForFailoverAndTwophase(Subscription *sub, const char *option,
+								   bool isTopLevel)
+{
+	StringInfoData cmd;
+
+	if (!sub->slotname)
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("cannot set %s for a subscription that does not have a slot name",
+						option)));
+
+	/*
+	 * Do not allow changing the option if the subscription is enabled. This
+	 * is because both failover and two_phase options of the slot on the
+	 * publisher cannot be modified if the slot is currently acquired by the
+	 * apply worker.
+	 */
+	if (sub->enabled)
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("cannot set %s for enabled subscription",
+						option)));
+
+	initStringInfo(&cmd);
+	appendStringInfo(&cmd, "ALTER SUBSCRIPTION ... SET (%s)", option);
+
+	/*
+	 * The changed option of the slot can't be rolled back: prevent we are in
+	 * the transaction state.
+	 */
+	PreventInTransactionBlock(isTopLevel, cmd.data);
+
+	pfree(cmd.data);
+}
+
 /*
  * Alter the existing subscription.
  */
@@ -1143,7 +1174,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 			{
 				supported_opts = (SUBOPT_SLOT_NAME |
 								  SUBOPT_SYNCHRONOUS_COMMIT | SUBOPT_BINARY |
-								  SUBOPT_STREAMING | SUBOPT_DISABLE_ON_ERR |
+								  SUBOPT_STREAMING | SUBOPT_TWOPHASE_COMMIT |
+								  SUBOPT_DISABLE_ON_ERR |
 								  SUBOPT_PASSWORD_REQUIRED |
 								  SUBOPT_RUN_AS_OWNER | SUBOPT_FAILOVER |
 								  SUBOPT_ORIGIN);
@@ -1227,33 +1259,61 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 
 				if (IsSet(opts.specified_opts, SUBOPT_FAILOVER))
 				{
-					if (!sub->slotname)
+					CommonChecksForFailoverAndTwophase(sub, "failover",
+													   isTopLevel);
+
+					values[Anum_pg_subscription_subfailover - 1] =
+						BoolGetDatum(opts.failover);
+					replaces[Anum_pg_subscription_subfailover - 1] = true;
+				}
+
+				if (IsSet(opts.specified_opts, SUBOPT_TWOPHASE_COMMIT))
+				{
+					CommonChecksForFailoverAndTwophase(sub, "two_phase",
+													   isTopLevel);
+
+					/*
+					 * slot_name and two_phase cannot be altered
+					 * simultaneously. The latter part refers to the pre-set
+					 * slot name and tries to modify the slot option, so
+					 * changing both does not make sense.
+					 */
+					if (IsSet(opts.specified_opts, SUBOPT_SLOT_NAME))
 						ereport(ERROR,
-								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-								 errmsg("cannot set %s for a subscription that does not have a slot name",
-										"failover")));
+								(errcode(ERRCODE_SYNTAX_ERROR),
+						 		 errmsg("slot_name and two_phase cannot be altered at the same time")));
 
 					/*
-					 * Do not allow changing the failover state if the
-					 * subscription is enabled. This is because the failover
-					 * state of the slot on the publisher cannot be modified
-					 * if the slot is currently acquired by the apply worker.
+					 * Workers may still survive even if the subscription has
+					 * been disabled. They may read the pg_subscription
+					 * catalog and detect that the twophase parameter is
+					 * updated, which causes the assertion failure. Ensure
+					 * workers have already been exited to avoid it.
 					 */
-					if (sub->enabled)
+					if (logicalrep_workers_find(subid, true, true))
 						ereport(ERROR,
 								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-								 errmsg("cannot set %s for enabled subscription",
-										"failover")));
+								 errmsg("cannot alter two_phase when logical replication worker is still running"),
+								 errhint("Wait certain time and try again.")));
 
 					/*
-					 * The changed failover option of the slot can't be rolled
-					 * back.
+					 * two_phase cannot be disabled if there are any
+					 * uncommitted prepared transactions present.
 					 */
-					PreventInTransactionBlock(isTopLevel, "ALTER SUBSCRIPTION ... SET (failover)");
-
-					values[Anum_pg_subscription_subfailover - 1] =
-						BoolGetDatum(opts.failover);
-					replaces[Anum_pg_subscription_subfailover - 1] = true;
+					if (!opts.twophase &&
+						sub->twophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
+						LookupGXactBySubid(subid))
+						ereport(ERROR,
+								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+								 errmsg("cannot disable two_phase when uncommitted prepared transactions present"),
+								 errhint("Resolve these transactions and try again")));
+
+					/* Change system catalog acoordingly */
+					values[Anum_pg_subscription_subtwophasestate - 1] =
+						CharGetDatum(opts.twophase ?
+									 LOGICALREP_TWOPHASE_STATE_PENDING :
+									 LOGICALREP_TWOPHASE_STATE_DISABLED);
+					replaces[Anum_pg_subscription_subtwophasestate - 1] = true;
 				}
 
 				if (IsSet(opts.specified_opts, SUBOPT_ORIGIN))
@@ -1505,7 +1565,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 	 * doing the database operations we won't be able to rollback altered
 	 * slot.
 	 */
-	if (replaces[Anum_pg_subscription_subfailover - 1])
+	if (replaces[Anum_pg_subscription_subfailover - 1] ||
+		replaces[Anum_pg_subscription_subtwophasestate - 1])
 	{
 		bool		must_use_password;
 		char	   *err;
@@ -1525,7 +1586,7 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 
 		PG_TRY();
 		{
-			walrcv_alter_slot(wrconn, sub->slotname, opts.failover);
+			walrcv_alter_slot(wrconn, sub->slotname, opts.failover, opts.twophase);
 		}
 		PG_FINALLY();
 		{
@@ -1672,9 +1733,7 @@ DropSubscription(DropSubscriptionStmt *stmt, bool isTopLevel)
 	 * New workers won't be started because we hold an exclusive lock on the
 	 * subscription till the end of the transaction.
 	 */
-	LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
-	subworkers = logicalrep_workers_find(subid, false);
-	LWLockRelease(LogicalRepWorkerLock);
+	subworkers = logicalrep_workers_find(subid, false, true);
 	foreach(lc, subworkers)
 	{
 		LogicalRepWorker *w = (LogicalRepWorker *) lfirst(lc);
diff --git a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
index 02f12f2921..2f035a0c3c 100644
--- a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
+++ b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
@@ -80,7 +80,7 @@ static char *libpqrcv_create_slot(WalReceiverConn *conn,
 								  CRSSnapshotAction snapshot_action,
 								  XLogRecPtr *lsn);
 static void libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-								bool failover);
+								bool failover, bool two_phase);
 static pid_t libpqrcv_get_backend_pid(WalReceiverConn *conn);
 static WalRcvExecResult *libpqrcv_exec(WalReceiverConn *conn,
 									   const char *query,
@@ -1121,15 +1121,16 @@ libpqrcv_create_slot(WalReceiverConn *conn, const char *slotname,
  */
 static void
 libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-					bool failover)
+					bool failover, bool two_phase)
 {
 	StringInfoData cmd;
 	PGresult   *res;
 
 	initStringInfo(&cmd);
-	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( FAILOVER %s )",
+	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( FAILOVER %s, TWO_PHASE %s )",
 					 quote_identifier(slotname),
-					 failover ? "true" : "false");
+					 failover ? "true" : "false",
+					 two_phase ? "true" : "false");
 
 	res = libpqrcv_PQexec(conn->streamConn, cmd.data);
 	pfree(cmd.data);
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 27c3a91fb7..45744b771f 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -272,12 +272,15 @@ logicalrep_worker_find(Oid subid, Oid relid, bool only_running)
  * the subscription, instead of just one.
  */
 List *
-logicalrep_workers_find(Oid subid, bool only_running)
+logicalrep_workers_find(Oid subid, bool only_running, bool require_lock)
 {
 	int			i;
 	List	   *res = NIL;
 
-	Assert(LWLockHeldByMe(LogicalRepWorkerLock));
+	if (require_lock)
+		LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
+	else
+		Assert(LWLockHeldByMe(LogicalRepWorkerLock));
 
 	/* Search for attached worker for a given subscription id. */
 	for (i = 0; i < max_logical_replication_workers; i++)
@@ -288,6 +291,9 @@ logicalrep_workers_find(Oid subid, bool only_running)
 			res = lappend(res, w);
 	}
 
+	if (require_lock)
+		LWLockRelease(LogicalRepWorkerLock);
+
 	return res;
 }
 
@@ -759,7 +765,7 @@ logicalrep_worker_detach(void)
 
 		LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
 
-		workers = logicalrep_workers_find(MyLogicalRepWorker->subid, true);
+		workers = logicalrep_workers_find(MyLogicalRepWorker->subid, true, false);
 		foreach(lc, workers)
 		{
 			LogicalRepWorker *w = (LogicalRepWorker *) lfirst(lc);
diff --git a/src/backend/replication/logical/worker.c b/src/backend/replication/logical/worker.c
index 3b285894db..33bfeb1fb2 100644
--- a/src/backend/replication/logical/worker.c
+++ b/src/backend/replication/logical/worker.c
@@ -401,9 +401,6 @@ static void apply_handle_tuple_routing(ApplyExecutionData *edata,
 									   LogicalRepTupleData *newtup,
 									   CmdType operation);
 
-/* Compute GID for two_phase transactions */
-static void TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid, int szgid);
-
 /* Functions for skipping changes */
 static void maybe_start_skipping_changes(XLogRecPtr finish_lsn);
 static void stop_skipping_changes(void);
@@ -3911,7 +3908,7 @@ maybe_reread_subscription(void)
 	/* !slotname should never happen when enabled is true. */
 	Assert(newsub->slotname);
 
-	/* two-phase should not be altered */
+	/* two-phase cannot be altered while the worker exists */
 	Assert(newsub->twophasestate == MySubscription->twophasestate);
 
 	/*
@@ -4396,24 +4393,6 @@ cleanup_subxact_info()
 	subxact_data.nsubxacts_max = 0;
 }
 
-/*
- * Form the prepared transaction GID for two_phase transactions.
- *
- * Return the GID in the supplied buffer.
- */
-static void
-TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid, int szgid)
-{
-	Assert(subid != InvalidRepOriginId);
-
-	if (!TransactionIdIsValid(xid))
-		ereport(ERROR,
-				(errcode(ERRCODE_PROTOCOL_VIOLATION),
-				 errmsg_internal("invalid two-phase transaction ID")));
-
-	snprintf(gid, szgid, "pg_gid_%u_%u", subid, xid);
-}
-
 /*
  * Common function to run the apply loop with error handling. Disable the
  * subscription, if necessary.
@@ -5013,7 +4992,7 @@ AtEOXact_LogicalRepWorkers(bool isCommit)
 			List	   *workers;
 			ListCell   *lc2;
 
-			workers = logicalrep_workers_find(subid, true);
+			workers = logicalrep_workers_find(subid, true, false);
 			foreach(lc2, workers)
 			{
 				LogicalRepWorker *worker = (LogicalRepWorker *) lfirst(lc2);
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index baf9b89dc4..2ad6dca993 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -804,8 +804,10 @@ ReplicationSlotDrop(const char *name, bool nowait)
  * Change the definition of the slot identified by the specified name.
  */
 void
-ReplicationSlotAlter(const char *name, bool failover)
+ReplicationSlotAlter(const char *name, bool failover, bool two_phase)
 {
+	bool		update_slot = false;
+
 	Assert(MyReplicationSlot == NULL);
 
 	ReplicationSlotAcquire(name, false);
@@ -854,6 +856,20 @@ ReplicationSlotAlter(const char *name, bool failover)
 		MyReplicationSlot->data.failover = failover;
 		SpinLockRelease(&MyReplicationSlot->mutex);
 
+		update_slot = true;
+	}
+
+	if (MyReplicationSlot->data.two_phase != two_phase)
+	{
+		SpinLockAcquire(&MyReplicationSlot->mutex);
+		MyReplicationSlot->data.two_phase = two_phase;
+		SpinLockRelease(&MyReplicationSlot->mutex);
+
+		update_slot = true;
+	}
+
+	if (update_slot)
+	{
 		ReplicationSlotMarkDirty();
 		ReplicationSlotSave();
 	}
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 754f505c13..af776fccb8 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1409,9 +1409,11 @@ DropReplicationSlot(DropReplicationSlotCmd *cmd)
  * Process extra options given to ALTER_REPLICATION_SLOT.
  */
 static void
-ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd, bool *failover)
+ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd,
+						  bool *failover, bool *two_phase)
 {
 	bool		failover_given = false;
+	bool		two_phase_given = false;
 
 	/* Parse options */
 	foreach_ptr(DefElem, defel, cmd->options)
@@ -1425,6 +1427,15 @@ ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd, bool *failover)
 			failover_given = true;
 			*failover = defGetBoolean(defel);
 		}
+		else if (strcmp(defel->defname, "two_phase") == 0)
+		{
+			if (two_phase_given)
+				ereport(ERROR,
+						(errcode(ERRCODE_SYNTAX_ERROR),
+						 errmsg("conflicting or redundant options")));
+			two_phase_given = true;
+			*two_phase = defGetBoolean(defel);
+		}
 		else
 			elog(ERROR, "unrecognized option: %s", defel->defname);
 	}
@@ -1437,9 +1448,10 @@ static void
 AlterReplicationSlot(AlterReplicationSlotCmd *cmd)
 {
 	bool		failover = false;
+	bool		two_phase = false;
 
-	ParseAlterReplSlotOptions(cmd, &failover);
-	ReplicationSlotAlter(cmd->slotname, failover);
+	ParseAlterReplSlotOptions(cmd, &failover, &two_phase);
+	ReplicationSlotAlter(cmd->slotname, failover, two_phase);
 }
 
 /*
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
index d453e224d9..891face1b6 100644
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -1948,7 +1948,7 @@ psql_completion(const char *text, int start, int end)
 	else if (HeadMatches("ALTER", "SUBSCRIPTION", MatchAny) && TailMatches("SET", "("))
 		COMPLETE_WITH("binary", "disable_on_error", "failover", "origin",
 					  "password_required", "run_as_owner", "slot_name",
-					  "streaming", "synchronous_commit");
+					  "streaming", "synchronous_commit", "two_phase");
 	/* ALTER SUBSCRIPTION <name> SKIP ( */
 	else if (HeadMatches("ALTER", "SUBSCRIPTION", MatchAny) && TailMatches("SKIP", "("))
 		COMPLETE_WITH("lsn");
diff --git a/src/include/access/twophase.h b/src/include/access/twophase.h
index 56248c0006..d37e06fdee 100644
--- a/src/include/access/twophase.h
+++ b/src/include/access/twophase.h
@@ -62,4 +62,9 @@ extern void PrepareRedoRemove(TransactionId xid, bool giveWarning);
 extern void restoreTwoPhaseData(void);
 extern bool LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 						TimestampTz origin_prepare_timestamp);
+
+extern void TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid,
+								   int szgid);
+extern bool LookupGXactBySubid(Oid subid);
+
 #endif							/* TWOPHASE_H */
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index c9675ee87c..163a4a911a 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -243,7 +243,8 @@ extern void ReplicationSlotCreate(const char *name, bool db_specific,
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
 extern void ReplicationSlotDropAcquired(void);
-extern void ReplicationSlotAlter(const char *name, bool failover);
+extern void ReplicationSlotAlter(const char *name, bool failover,
+								 bool two_phase);
 
 extern void ReplicationSlotAcquire(const char *name, bool nowait);
 extern void ReplicationSlotRelease(void);
diff --git a/src/include/replication/walreceiver.h b/src/include/replication/walreceiver.h
index 12f71fa99b..31fa1257ec 100644
--- a/src/include/replication/walreceiver.h
+++ b/src/include/replication/walreceiver.h
@@ -372,12 +372,13 @@ typedef char *(*walrcv_create_slot_fn) (WalReceiverConn *conn,
 /*
  * walrcv_alter_slot_fn
  *
- * Change the definition of a replication slot. Currently, it only supports
- * changing the failover property of the slot.
+ * Change the definition of a replication slot. Currently, it supports
+ * changing the failover and the two_phase property of the slot.
  */
 typedef void (*walrcv_alter_slot_fn) (WalReceiverConn *conn,
 									  const char *slotname,
-									  bool failover);
+									  bool failover,
+									  bool two_phase);
 
 /*
  * walrcv_get_backend_pid_fn
@@ -455,8 +456,8 @@ extern PGDLLIMPORT WalReceiverFunctionsType *WalReceiverFunctions;
 	WalReceiverFunctions->walrcv_send(conn, buffer, nbytes)
 #define walrcv_create_slot(conn, slotname, temporary, two_phase, failover, snapshot_action, lsn) \
 	WalReceiverFunctions->walrcv_create_slot(conn, slotname, temporary, two_phase, failover, snapshot_action, lsn)
-#define walrcv_alter_slot(conn, slotname, failover) \
-	WalReceiverFunctions->walrcv_alter_slot(conn, slotname, failover)
+#define walrcv_alter_slot(conn, slotname, failover, two_phase) \
+	WalReceiverFunctions->walrcv_alter_slot(conn, slotname, failover, two_phase)
 #define walrcv_get_backend_pid(conn) \
 	WalReceiverFunctions->walrcv_get_backend_pid(conn)
 #define walrcv_exec(conn, exec, nRetTypes, retTypes) \
diff --git a/src/include/replication/worker_internal.h b/src/include/replication/worker_internal.h
index 515aefd519..990f5242f9 100644
--- a/src/include/replication/worker_internal.h
+++ b/src/include/replication/worker_internal.h
@@ -240,7 +240,8 @@ extern PGDLLIMPORT bool InitializingApplyWorker;
 extern void logicalrep_worker_attach(int slot);
 extern LogicalRepWorker *logicalrep_worker_find(Oid subid, Oid relid,
 												bool only_running);
-extern List *logicalrep_workers_find(Oid subid, bool only_running);
+extern List *logicalrep_workers_find(Oid subid, bool only_running,
+									 bool require_lock);
 extern bool logicalrep_worker_launch(LogicalRepWorkerType wtype,
 									 Oid dbid, Oid subid, const char *subname,
 									 Oid userid, Oid relid,
diff --git a/src/test/regress/expected/subscription.out b/src/test/regress/expected/subscription.out
index 0f2a25cdc1..51fa4b9690 100644
--- a/src/test/regress/expected/subscription.out
+++ b/src/test/regress/expected/subscription.out
@@ -377,10 +377,7 @@ HINT:  To initiate replication, you must manually create the replication slot, e
  regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | p                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
---fail - alter of two_phase option not supported.
-ALTER SUBSCRIPTION regress_testsub SET (two_phase = false);
-ERROR:  unrecognized subscription parameter: "two_phase"
--- but can alter streaming when two_phase enabled
+-- We can alter streaming when two_phase enabled
 ALTER SUBSCRIPTION regress_testsub SET (streaming = true);
 \dRs+
                                                                                                                 List of subscriptions
diff --git a/src/test/regress/sql/subscription.sql b/src/test/regress/sql/subscription.sql
index 3e5ba4cb8c..a3886d79ca 100644
--- a/src/test/regress/sql/subscription.sql
+++ b/src/test/regress/sql/subscription.sql
@@ -256,10 +256,7 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUBLICATION testpub WITH (connect = false, two_phase = true);
 
 \dRs+
---fail - alter of two_phase option not supported.
-ALTER SUBSCRIPTION regress_testsub SET (two_phase = false);
-
--- but can alter streaming when two_phase enabled
+-- We can alter streaming when two_phase enabled
 ALTER SUBSCRIPTION regress_testsub SET (streaming = true);
 
 \dRs+
diff --git a/src/test/subscription/t/021_twophase.pl b/src/test/subscription/t/021_twophase.pl
index 9437cd4c3b..4e8f627f7b 100644
--- a/src/test/subscription/t/021_twophase.pl
+++ b/src/test/subscription/t/021_twophase.pl
@@ -367,6 +367,81 @@ $result =
   $node_subscriber->safe_psql('postgres', "SELECT count(*) FROM tab_copy;");
 is($result, qq(2), 'replicated data in subscriber table');
 
+# Clean up
+$node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub");
+
+###############################
+# Disable the subscription and alter it to two_phase = false,
+# then verify that the altered subscription reflects the two_phase option.
+###############################
+
+# Alter subscription two_phase to false
+$node_subscriber->safe_psql('postgres',
+    "ALTER SUBSCRIPTION tap_sub_copy DISABLE;");
+$node_subscriber->poll_query_until('postgres',
+    "SELECT count(*) = 0 FROM pg_stat_activity WHERE backend_type = 'logical replication worker'"
+);
+$node_subscriber->safe_psql(
+	'postgres', "
+    ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = false);
+    ALTER SUBSCRIPTION tap_sub_copy ENABLE;");
+
+# Wait for subscription startup
+$node_subscriber->wait_for_subscription_sync($node_publisher, $appname_copy);
+
+# Make sure that the two-phase is disabled on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT subtwophasestate FROM pg_subscription WHERE subname = 'tap_sub_copy';"
+);
+is($result, qq(d), 'two-phase should be disabled');
+
+# Now do a prepare on the publisher and make sure that it is not replicated.
+$node_publisher->safe_psql(
+	'postgres', qq{
+    BEGIN;
+    INSERT INTO tab_copy VALUES (100);
+    PREPARE TRANSACTION 'newgid';
+	});
+
+# Wait for the subscriber to catchup
+$node_publisher->wait_for_catchup($appname_copy);
+
+# Make sure there are no prepared transactions on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT count(*) FROM pg_prepared_xacts;");
+is($result, qq(0), 'should be no prepared transactions on subscriber');
+
+# Now commit the insert and verify that it is replicated
+$node_publisher->safe_psql('postgres', "COMMIT PREPARED 'newgid';");
+
+# Wait for the subscriber to catchup
+$node_publisher->wait_for_catchup($appname_copy);
+
+# Make sure that the committed transaction is replicated.
+$result =
+  $node_subscriber->safe_psql('postgres', "SELECT count(*) FROM tab_copy;");
+is($result, qq(3), 'replicated data in subscriber table');
+
+# Alter subscription two_phase to true
+$node_subscriber->safe_psql('postgres',
+    "ALTER SUBSCRIPTION tap_sub_copy DISABLE;");
+$node_subscriber->poll_query_until('postgres',
+    "SELECT count(*) = 0 FROM pg_stat_activity WHERE backend_type = 'logical replication worker'"
+);
+$node_subscriber->safe_psql(
+	'postgres', "
+    ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = true);
+    ALTER SUBSCRIPTION tap_sub_copy ENABLE;");
+
+# Wait for subscription startup
+$node_subscriber->wait_for_subscription_sync($node_publisher, $appname_copy);
+
+# Make sure that the two-phase is enabled on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT subtwophasestate FROM pg_subscription WHERE subname = 'tap_sub_copy';"
+);
+is($result, qq(e), 'two-phase should be enabled');
+
 $node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub_copy;");
 $node_publisher->safe_psql('postgres', "DROP PUBLICATION tap_pub_copy;");
 
@@ -374,8 +449,6 @@ $node_publisher->safe_psql('postgres', "DROP PUBLICATION tap_pub_copy;");
 # check all the cleanup
 ###############################
 
-$node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub");
-
 $result = $node_subscriber->safe_psql('postgres',
 	"SELECT count(*) FROM pg_subscription");
 is($result, qq(0), 'check subscription was dropped on subscriber');
-- 
2.43.0

From 5df654692988e3880b6132c53f218e511cf6f51d Mon Sep 17 00:00:00 2001
From: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Date: Wed, 17 Apr 2024 06:18:23 +0000
Subject: [PATCH v17 2/3] Alter slot option two_phase only when altering "true"
 to "false"

Since the two_phase option is controlled by both the publisher (as a slot option)
and the subscriber (as a subscription option), the slot option must also be
modified.

Regarding the false->true case, the backend process alters the subtwophase to
LOGICALREP_TWOPHASE_STATE_PENDING once. After the subscription is enabled, a new
logical replication worker requests to change the two_phase option of its slot
from pending to true after the initial data synchronization is done. The code
path is the same as the case in which two_phase is initially set to true, so
there is no need to do something remarkable. However, for the true->false case,
the backend must connect to the publisher and expressly change the parameter
because the apply worker does not alter the option to false. Because this
operation cannot be rolled back, altering the two_phase parameter from "true"
to "false" within a transaction is prohibited.
---
 doc/src/sgml/ref/alter_subscription.sgml      |  2 +-
 src/backend/commands/subscriptioncmds.c       | 76 ++++++++++++++-----
 .../libpqwalreceiver/libpqwalreceiver.c       | 23 ++++--
 src/include/replication/walreceiver.h         |  5 +-
 src/test/subscription/t/021_twophase.pl       | 41 ++++++----
 5 files changed, 102 insertions(+), 45 deletions(-)

diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index 0b23df1b77..475a42a2e3 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -70,7 +70,7 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
    <command>ALTER SUBSCRIPTION ... {SET|ADD|DROP} PUBLICATION ...</command>
    with <literal>refresh</literal> option as <literal>true</literal>,
    <command>ALTER SUBSCRIPTION ... SET (failover = true|false)</command> and
-   <command>ALTER SUBSCRIPTION ... SET (two_phase = true|false)</command>
+   <command>ALTER SUBSCRIPTION ... SET (two_phase = off)</command>
    cannot be executed inside a transaction block.
 
    These commands also cannot be executed when the subscription has
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index 255628c396..3729956147 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -112,6 +112,7 @@ static List *merge_publications(List *oldpublist, List *newpublist, bool addpub,
 static void ReportSlotConnectionError(List *rstates, Oid subid, char *slotname, char *err);
 static void CommonChecksForFailoverAndTwophase(Subscription *sub,
 											   const char *option,
+											   bool needs_update,
 											   bool isTopLevel);
 
 
@@ -1074,11 +1075,9 @@ AlterSubscription_refresh(Subscription *sub, bool copy_data,
  */
 static void
 CommonChecksForFailoverAndTwophase(Subscription *sub, const char *option,
-								   bool isTopLevel)
+								   bool needs_update, bool isTopLevel)
 {
-	StringInfoData cmd;
-
-	if (!sub->slotname)
+	if (needs_update && !sub->slotname)
 		ereport(ERROR,
 				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
 				 errmsg("cannot set %s for a subscription that does not have a slot name",
@@ -1096,16 +1095,20 @@ CommonChecksForFailoverAndTwophase(Subscription *sub, const char *option,
 				 errmsg("cannot set %s for enabled subscription",
 						option)));
 
-	initStringInfo(&cmd);
-	appendStringInfo(&cmd, "ALTER SUBSCRIPTION ... SET (%s)", option);
-
 	/*
 	 * The changed option of the slot can't be rolled back: prevent we are in
 	 * the transaction state.
 	 */
-	PreventInTransactionBlock(isTopLevel, cmd.data);
+	if (needs_update)
+	{
+		StringInfoData cmd;
 
-	pfree(cmd.data);
+		initStringInfo(&cmd);
+		appendStringInfo(&cmd, "ALTER SUBSCRIPTION ... SET (%s)", option);
+
+		PreventInTransactionBlock(isTopLevel, cmd.data);
+		pfree(cmd.data);
+	}
 }
 
 /*
@@ -1127,6 +1130,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 	Form_pg_subscription form;
 	bits32		supported_opts;
 	SubOpts		opts = {0};
+	bool		update_failover;
+	bool		update_two_phase;
 
 	rel = table_open(SubscriptionRelationId, RowExclusiveLock);
 
@@ -1259,8 +1264,16 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 
 				if (IsSet(opts.specified_opts, SUBOPT_FAILOVER))
 				{
+					/*
+					 * First mark the needs to alter the replication slot.
+					 * Failover option is controlled by both the publisher (as
+					 * a slot option) and the subscriber (as a subscription
+					 * option).
+					 */
+					update_failover = true;
+
 					CommonChecksForFailoverAndTwophase(sub, "failover",
-													   isTopLevel);
+													   update_failover, isTopLevel);
 
 					values[Anum_pg_subscription_subfailover - 1] =
 						BoolGetDatum(opts.failover);
@@ -1269,16 +1282,36 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 
 				if (IsSet(opts.specified_opts, SUBOPT_TWOPHASE_COMMIT))
 				{
+					/*
+					 * First check the need to alter the replication slot.
+					 * Two_phase option is controlled by both the publisher
+					 * (as a slot option) and the subscriber (as a
+					 * subscription option). The slot option must be altered
+					 * only when changing "true" to "false".
+					 *
+					 * There is no need to do something remarkable regarding
+					 * the "false" to "true" case; the backend process alters
+					 * subtwophase to LOGICALREP_TWOPHASE_STATE_PENDING once.
+					 * After the subscription is enabled, a new logical
+					 * replication worker requests to change the two_phase
+					 * option of its slot from pending to true when the
+					 * initial data synchronization is done. The code path is
+					 * the same as the case in which two_phase is initially
+					 * set to true.
+					 */
+					update_two_phase = !opts.twophase;
+
 					CommonChecksForFailoverAndTwophase(sub, "two_phase",
-													   isTopLevel);
+													   update_two_phase, isTopLevel);
 
 					/*
-					 * slot_name and two_phase cannot be altered
-					 * simultaneously. The latter part refers to the pre-set
-					 * slot name and tries to modify the slot option, so
-					 * changing both does not make sense.
+					 * If the wo_phase slot option must be altered, this cannot
+					 * be altered with slot_name simultaneously. The latter
+					 * part refers to the pre-set slot name and tries to modify
+					 * the slot option, so changing both does not make sense.
 					 */
-					if (IsSet(opts.specified_opts, SUBOPT_SLOT_NAME))
+					if (update_two_phase &&
+						IsSet(opts.specified_opts, SUBOPT_SLOT_NAME))
 						ereport(ERROR,
 								(errcode(ERRCODE_SYNTAX_ERROR),
 						 		 errmsg("slot_name and two_phase cannot be altered at the same time")));
@@ -1300,7 +1333,7 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 					 * two_phase cannot be disabled if there are any
 					 * uncommitted prepared transactions present.
 					 */
-					if (!opts.twophase &&
+					if (update_two_phase &&
 						sub->twophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
 						LookupGXactBySubid(subid))
 						ereport(ERROR,
@@ -1559,14 +1592,13 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 	}
 
 	/*
-	 * Try to acquire the connection necessary for altering slot.
+	 * Try to acquire the connection necessary for altering slot, if needed.
 	 *
 	 * This has to be at the end because otherwise if there is an error while
 	 * doing the database operations we won't be able to rollback altered
 	 * slot.
 	 */
-	if (replaces[Anum_pg_subscription_subfailover - 1] ||
-		replaces[Anum_pg_subscription_subtwophasestate - 1])
+	if (update_failover || update_two_phase)
 	{
 		bool		must_use_password;
 		char	   *err;
@@ -1586,7 +1618,9 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 
 		PG_TRY();
 		{
-			walrcv_alter_slot(wrconn, sub->slotname, opts.failover, opts.twophase);
+			walrcv_alter_slot(wrconn, sub->slotname,
+							  update_failover ? &opts.failover : NULL,
+							  update_two_phase ? &opts.twophase : NULL);
 		}
 		PG_FINALLY();
 		{
diff --git a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
index 2f035a0c3c..07dfec947d 100644
--- a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
+++ b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
@@ -80,7 +80,7 @@ static char *libpqrcv_create_slot(WalReceiverConn *conn,
 								  CRSSnapshotAction snapshot_action,
 								  XLogRecPtr *lsn);
 static void libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-								bool failover, bool two_phase);
+								const bool *failover, const bool *two_phase);
 static pid_t libpqrcv_get_backend_pid(WalReceiverConn *conn);
 static WalRcvExecResult *libpqrcv_exec(WalReceiverConn *conn,
 									   const char *query,
@@ -1121,16 +1121,27 @@ libpqrcv_create_slot(WalReceiverConn *conn, const char *slotname,
  */
 static void
 libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-					bool failover, bool two_phase)
+					const bool *failover, const bool *two_phase)
 {
 	StringInfoData cmd;
 	PGresult   *res;
 
 	initStringInfo(&cmd);
-	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( FAILOVER %s, TWO_PHASE %s )",
-					 quote_identifier(slotname),
-					 failover ? "true" : "false",
-					 two_phase ? "true" : "false");
+	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( ",
+					 quote_identifier(slotname));
+
+	if (failover)
+		appendStringInfo(&cmd, "FAILOVER %s",
+						 *failover ? "true" : "false");
+
+	if (failover && two_phase)
+		appendStringInfo(&cmd, ", ");
+
+	if (two_phase)
+		appendStringInfo(&cmd, "TWO_PHASE %s",
+						 *two_phase ? "true" : "false");
+
+	appendStringInfoString(&cmd, " );");
 
 	res = libpqrcv_PQexec(conn->streamConn, cmd.data);
 	pfree(cmd.data);
diff --git a/src/include/replication/walreceiver.h b/src/include/replication/walreceiver.h
index 31fa1257ec..7ffa5a58b3 100644
--- a/src/include/replication/walreceiver.h
+++ b/src/include/replication/walreceiver.h
@@ -377,8 +377,9 @@ typedef char *(*walrcv_create_slot_fn) (WalReceiverConn *conn,
  */
 typedef void (*walrcv_alter_slot_fn) (WalReceiverConn *conn,
 									  const char *slotname,
-									  bool failover,
-									  bool two_phase);
+									  const bool *failover,
+									  const bool *two_phase);
+
 
 /*
  * walrcv_get_backend_pid_fn
diff --git a/src/test/subscription/t/021_twophase.pl b/src/test/subscription/t/021_twophase.pl
index 4e8f627f7b..f56dff4b12 100644
--- a/src/test/subscription/t/021_twophase.pl
+++ b/src/test/subscription/t/021_twophase.pl
@@ -375,6 +375,12 @@ $node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub");
 # then verify that the altered subscription reflects the two_phase option.
 ###############################
 
+# Confirm two-phase slot option is enabled before altering
+$result = $node_publisher->safe_psql('postgres',
+	"SELECT two_phase FROM pg_replication_slots WHERE slot_name = 'tap_sub_copy';"
+);
+is($result, qq(t), 'two-phase is enabled');
+
 # Alter subscription two_phase to false
 $node_subscriber->safe_psql('postgres',
     "ALTER SUBSCRIPTION tap_sub_copy DISABLE;");
@@ -393,7 +399,13 @@ $node_subscriber->wait_for_subscription_sync($node_publisher, $appname_copy);
 $result = $node_subscriber->safe_psql('postgres',
 	"SELECT subtwophasestate FROM pg_subscription WHERE subname = 'tap_sub_copy';"
 );
-is($result, qq(d), 'two-phase should be disabled');
+is($result, qq(d), 'two-phase subscription option should be disabled');
+
+# Make sure that the two-phase slot option is also disabled
+$result = $node_publisher->safe_psql('postgres',
+	"SELECT two_phase FROM pg_replication_slots WHERE slot_name = 'tap_sub_copy';"
+);
+is($result, qq(f), 'two-phase slot option should be disabled');
 
 # Now do a prepare on the publisher and make sure that it is not replicated.
 $node_publisher->safe_psql(
@@ -411,6 +423,19 @@ $result = $node_subscriber->safe_psql('postgres',
 	"SELECT count(*) FROM pg_prepared_xacts;");
 is($result, qq(0), 'should be no prepared transactions on subscriber');
 
+# Toggle the two_phase to "true" *before* the COMMIT PREPARED. Since we are the
+# special path for the case where both two_phase and failover are altered, it
+# is also set to "true".
+$node_subscriber->safe_psql('postgres',
+    "ALTER SUBSCRIPTION tap_sub_copy DISABLE;");
+$node_subscriber->poll_query_until('postgres',
+    "SELECT count(*) = 0 FROM pg_stat_activity WHERE backend_type = 'logical replication worker'"
+);
+$node_subscriber->safe_psql(
+	'postgres', "
+    ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = true, failover = true);
+    ALTER SUBSCRIPTION tap_sub_copy ENABLE;");
+
 # Now commit the insert and verify that it is replicated
 $node_publisher->safe_psql('postgres', "COMMIT PREPARED 'newgid';");
 
@@ -422,20 +447,6 @@ $result =
   $node_subscriber->safe_psql('postgres', "SELECT count(*) FROM tab_copy;");
 is($result, qq(3), 'replicated data in subscriber table');
 
-# Alter subscription two_phase to true
-$node_subscriber->safe_psql('postgres',
-    "ALTER SUBSCRIPTION tap_sub_copy DISABLE;");
-$node_subscriber->poll_query_until('postgres',
-    "SELECT count(*) = 0 FROM pg_stat_activity WHERE backend_type = 'logical replication worker'"
-);
-$node_subscriber->safe_psql(
-	'postgres', "
-    ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = true);
-    ALTER SUBSCRIPTION tap_sub_copy ENABLE;");
-
-# Wait for subscription startup
-$node_subscriber->wait_for_subscription_sync($node_publisher, $appname_copy);
-
 # Make sure that the two-phase is enabled on the subscriber
 $result = $node_subscriber->safe_psql('postgres',
 	"SELECT subtwophasestate FROM pg_subscription WHERE subname = 'tap_sub_copy';"
-- 
2.43.0

From e425e241341e61eed3ab2e1969d53990cb033c84 Mon Sep 17 00:00:00 2001
From: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Date: Tue, 9 Jul 2024 08:01:43 +0000
Subject: [PATCH v17 3/3] Notify users to roll back prepared transactions

---
 doc/src/sgml/ref/alter_subscription.sgml | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index 475a42a2e3..5263fe7c68 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -233,8 +233,6 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>, and
       <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>.
       Only a superuser can set <literal>password_required = false</literal>.
-      The <literal>two_phase</literal> parameter can only be altered when the
-      subscription is disabled.
      </para>
 
      <para>
@@ -256,6 +254,19 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>
       option is enabled.
      </para>
+
+     <para>
+      The <literal>two_phase</literal> parameter can only be altered when the
+      subscription is disabled. When altering the parameter from <literal>true</literal>
+      to <literal>false</literal>, the backend process checks for any incomplete
+      prepared transactions done by the logical replication worker (from when
+      <literal>two_phase</literal> parameter was still <literal>true</literal>)
+      and, if any are found, this command is failed with an error. In this
+      case, you can resolve prepared transactions on the publisher node or
+      manually roll back them on the subscriber. Alter the altering from
+      <literal>true</literal> to <literal>false</literal>, the publisher will
+      replicate transactions again when they are committed.
+     </para>
     </listitem>
    </varlistentry>
 
-- 
2.43.0

From 0006608c5b65941f43c5ce622f64144f2030adff Mon Sep 17 00:00:00 2001
From: Ajin Cherian <ajinc@fast.au.fujitsu.com>
Date: Fri, 5 Apr 2024 06:47:18 -0400
Subject: [PATCH v17 1/3] Allow altering of two_phase option of a SUBSCRIPTION

This patch allows the user to alter the 'two_phase' option of a subscriber provided no
uncommitted prepared transactions are pending on that subscription.

Author: Cherian Ajin, Hayato Kuroda
---
 doc/src/sgml/ref/alter_subscription.sgml      |  12 +-
 src/backend/access/transam/twophase.c         |  62 ++++++++
 src/backend/commands/subscriptioncmds.c       | 135 +++++++++++++-----
 .../libpqwalreceiver/libpqwalreceiver.c       |   9 +-
 src/backend/replication/logical/launcher.c    |  12 +-
 src/backend/replication/logical/worker.c      |  25 +---
 src/backend/replication/slot.c                |  18 ++-
 src/backend/replication/walsender.c           |  18 ++-
 src/bin/psql/tab-complete.c                   |   2 +-
 src/include/access/twophase.h                 |   5 +
 src/include/replication/slot.h                |   3 +-
 src/include/replication/walreceiver.h         |  11 +-
 src/include/replication/worker_internal.h     |   3 +-
 src/test/regress/expected/subscription.out    |   5 +-
 src/test/regress/sql/subscription.sql         |   5 +-
 src/test/subscription/t/021_twophase.pl       |  77 +++++++++-
 16 files changed, 308 insertions(+), 94 deletions(-)

diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index 476f195622..0b23df1b77 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -68,8 +68,9 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
   <para>
    Commands <command>ALTER SUBSCRIPTION ... REFRESH PUBLICATION</command>,
    <command>ALTER SUBSCRIPTION ... {SET|ADD|DROP} PUBLICATION ...</command>
-   with <literal>refresh</literal> option as <literal>true</literal> and
-   <command>ALTER SUBSCRIPTION ... SET (failover = true|false)</command>
+   with <literal>refresh</literal> option as <literal>true</literal>,
+   <command>ALTER SUBSCRIPTION ... SET (failover = true|false)</command> and
+   <command>ALTER SUBSCRIPTION ... SET (two_phase = true|false)</command>
    cannot be executed inside a transaction block.
 
    These commands also cannot be executed when the subscription has
@@ -228,9 +229,12 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-disable-on-error"><literal>disable_on_error</literal></link>,
       <link linkend="sql-createsubscription-params-with-password-required"><literal>password_required</literal></link>,
       <link linkend="sql-createsubscription-params-with-run-as-owner"><literal>run_as_owner</literal></link>,
-      <link linkend="sql-createsubscription-params-with-origin"><literal>origin</literal></link>, and
-      <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>.
+      <link linkend="sql-createsubscription-params-with-origin"><literal>origin</literal></link>,
+      <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>, and
+      <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>.
       Only a superuser can set <literal>password_required = false</literal>.
+      The <literal>two_phase</literal> parameter can only be altered when the
+      subscription is disabled.
      </para>
 
      <para>
diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index 9a8257fcaf..35bce6809d 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -2681,3 +2681,65 @@ LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 	LWLockRelease(TwoPhaseStateLock);
 	return found;
 }
+
+/*
+ * TwoPhaseTransactionGid
+ *		Form the prepared transaction GID for two_phase transactions.
+ *
+ * Return the GID in the supplied buffer.
+ */
+void
+TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid, int szgid)
+{
+	Assert(subid != InvalidRepOriginId);
+
+	if (!TransactionIdIsValid(xid))
+		ereport(ERROR,
+				(errcode(ERRCODE_PROTOCOL_VIOLATION),
+				 errmsg_internal("invalid two-phase transaction ID")));
+
+	snprintf(gid, szgid, "pg_gid_%u_%u", subid, xid);
+}
+
+/*
+ * IsTwoPhaseTransactionGidForSubid
+ *		Check whether the given GID (as formed by TwoPhaseTransactionGid) is
+ *		for the specified 'subid'.
+ */
+static bool
+IsTwoPhaseTransactionGidForSubid(Oid subid, char *gid)
+{
+	int			ret;
+	Oid			subid_written;
+	TransactionId xid;
+
+	ret = sscanf(gid, "pg_gid_%u_%u", &subid_written, &xid);
+
+	return (ret == 2 && subid == subid_written);
+}
+
+/*
+ * LookupGXactBySubid
+ *		Check if the prepared transaction done by apply worker exists.
+ */
+bool
+LookupGXactBySubid(Oid subid)
+{
+	bool		found = false;
+
+	LWLockAcquire(TwoPhaseStateLock, LW_SHARED);
+	for (int i = 0; i < TwoPhaseState->numPrepXacts; i++)
+	{
+		GlobalTransaction gxact = TwoPhaseState->prepXacts[i];
+
+		/* Ignore not-yet-valid GIDs. */
+		if (gxact->valid &&
+			IsTwoPhaseTransactionGidForSubid(subid, gxact->gid))
+		{
+			found = true;
+			break;
+		}
+	}
+	LWLockRelease(TwoPhaseStateLock);
+	return found;
+}
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index e407428dbc..255628c396 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -16,6 +16,7 @@
 
 #include "access/htup_details.h"
 #include "access/table.h"
+#include "access/twophase.h"
 #include "access/xact.h"
 #include "catalog/catalog.h"
 #include "catalog/dependency.h"
@@ -109,6 +110,9 @@ static void check_publications_origin(WalReceiverConn *wrconn,
 static void check_duplicates_in_publist(List *publist, Datum *datums);
 static List *merge_publications(List *oldpublist, List *newpublist, bool addpub, const char *subname);
 static void ReportSlotConnectionError(List *rstates, Oid subid, char *slotname, char *err);
+static void CommonChecksForFailoverAndTwophase(Subscription *sub,
+											   const char *option,
+											   bool isTopLevel);
 
 
 /*
@@ -259,21 +263,9 @@ parse_subscription_options(ParseState *pstate, List *stmt_options,
 			opts->specified_opts |= SUBOPT_STREAMING;
 			opts->streaming = defGetStreamingMode(defel);
 		}
-		else if (strcmp(defel->defname, "two_phase") == 0)
+		else if (IsSet(supported_opts, SUBOPT_TWOPHASE_COMMIT) &&
+				 strcmp(defel->defname, "two_phase") == 0)
 		{
-			/*
-			 * Do not allow toggling of two_phase option. Doing so could cause
-			 * missing of transactions and lead to an inconsistent replica.
-			 * See comments atop worker.c
-			 *
-			 * Note: Unsupported twophase indicates that this call originated
-			 * from AlterSubscription.
-			 */
-			if (!IsSet(supported_opts, SUBOPT_TWOPHASE_COMMIT))
-				ereport(ERROR,
-						(errcode(ERRCODE_SYNTAX_ERROR),
-						 errmsg("unrecognized subscription parameter: \"%s\"", defel->defname)));
-
 			if (IsSet(opts->specified_opts, SUBOPT_TWOPHASE_COMMIT))
 				errorConflictingDefElem(defel, pstate);
 
@@ -1077,6 +1069,45 @@ AlterSubscription_refresh(Subscription *sub, bool copy_data,
 		table_close(rel, NoLock);
 }
 
+/*
+ * Common checks for altering failover and two_phase option
+ */
+static void
+CommonChecksForFailoverAndTwophase(Subscription *sub, const char *option,
+								   bool isTopLevel)
+{
+	StringInfoData cmd;
+
+	if (!sub->slotname)
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("cannot set %s for a subscription that does not have a slot name",
+						option)));
+
+	/*
+	 * Do not allow changing the option if the subscription is enabled. This
+	 * is because both failover and two_phase options of the slot on the
+	 * publisher cannot be modified if the slot is currently acquired by the
+	 * apply worker.
+	 */
+	if (sub->enabled)
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("cannot set %s for enabled subscription",
+						option)));
+
+	initStringInfo(&cmd);
+	appendStringInfo(&cmd, "ALTER SUBSCRIPTION ... SET (%s)", option);
+
+	/*
+	 * The changed option of the slot can't be rolled back: prevent we are in
+	 * the transaction state.
+	 */
+	PreventInTransactionBlock(isTopLevel, cmd.data);
+
+	pfree(cmd.data);
+}
+
 /*
  * Alter the existing subscription.
  */
@@ -1143,7 +1174,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 			{
 				supported_opts = (SUBOPT_SLOT_NAME |
 								  SUBOPT_SYNCHRONOUS_COMMIT | SUBOPT_BINARY |
-								  SUBOPT_STREAMING | SUBOPT_DISABLE_ON_ERR |
+								  SUBOPT_STREAMING | SUBOPT_TWOPHASE_COMMIT |
+								  SUBOPT_DISABLE_ON_ERR |
 								  SUBOPT_PASSWORD_REQUIRED |
 								  SUBOPT_RUN_AS_OWNER | SUBOPT_FAILOVER |
 								  SUBOPT_ORIGIN);
@@ -1227,33 +1259,61 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 
 				if (IsSet(opts.specified_opts, SUBOPT_FAILOVER))
 				{
-					if (!sub->slotname)
+					CommonChecksForFailoverAndTwophase(sub, "failover",
+													   isTopLevel);
+
+					values[Anum_pg_subscription_subfailover - 1] =
+						BoolGetDatum(opts.failover);
+					replaces[Anum_pg_subscription_subfailover - 1] = true;
+				}
+
+				if (IsSet(opts.specified_opts, SUBOPT_TWOPHASE_COMMIT))
+				{
+					CommonChecksForFailoverAndTwophase(sub, "two_phase",
+													   isTopLevel);
+
+					/*
+					 * slot_name and two_phase cannot be altered
+					 * simultaneously. The latter part refers to the pre-set
+					 * slot name and tries to modify the slot option, so
+					 * changing both does not make sense.
+					 */
+					if (IsSet(opts.specified_opts, SUBOPT_SLOT_NAME))
 						ereport(ERROR,
-								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-								 errmsg("cannot set %s for a subscription that does not have a slot name",
-										"failover")));
+								(errcode(ERRCODE_SYNTAX_ERROR),
+						 		 errmsg("slot_name and two_phase cannot be altered at the same time")));
 
 					/*
-					 * Do not allow changing the failover state if the
-					 * subscription is enabled. This is because the failover
-					 * state of the slot on the publisher cannot be modified
-					 * if the slot is currently acquired by the apply worker.
+					 * Workers may still survive even if the subscription has
+					 * been disabled. They may read the pg_subscription
+					 * catalog and detect that the twophase parameter is
+					 * updated, which causes the assertion failure. Ensure
+					 * workers have already been exited to avoid it.
 					 */
-					if (sub->enabled)
+					if (logicalrep_workers_find(subid, true, true))
 						ereport(ERROR,
 								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-								 errmsg("cannot set %s for enabled subscription",
-										"failover")));
+								 errmsg("cannot alter two_phase when logical replication worker is still running"),
+								 errhint("Wait certain time and try again.")));
 
 					/*
-					 * The changed failover option of the slot can't be rolled
-					 * back.
+					 * two_phase cannot be disabled if there are any
+					 * uncommitted prepared transactions present.
 					 */
-					PreventInTransactionBlock(isTopLevel, "ALTER SUBSCRIPTION ... SET (failover)");
-
-					values[Anum_pg_subscription_subfailover - 1] =
-						BoolGetDatum(opts.failover);
-					replaces[Anum_pg_subscription_subfailover - 1] = true;
+					if (!opts.twophase &&
+						sub->twophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
+						LookupGXactBySubid(subid))
+						ereport(ERROR,
+								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+								 errmsg("cannot disable two_phase when uncommitted prepared transactions present"),
+								 errhint("Resolve these transactions and try again")));
+
+					/* Change system catalog acoordingly */
+					values[Anum_pg_subscription_subtwophasestate - 1] =
+						CharGetDatum(opts.twophase ?
+									 LOGICALREP_TWOPHASE_STATE_PENDING :
+									 LOGICALREP_TWOPHASE_STATE_DISABLED);
+					replaces[Anum_pg_subscription_subtwophasestate - 1] = true;
 				}
 
 				if (IsSet(opts.specified_opts, SUBOPT_ORIGIN))
@@ -1505,7 +1565,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 	 * doing the database operations we won't be able to rollback altered
 	 * slot.
 	 */
-	if (replaces[Anum_pg_subscription_subfailover - 1])
+	if (replaces[Anum_pg_subscription_subfailover - 1] ||
+		replaces[Anum_pg_subscription_subtwophasestate - 1])
 	{
 		bool		must_use_password;
 		char	   *err;
@@ -1525,7 +1586,7 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 
 		PG_TRY();
 		{
-			walrcv_alter_slot(wrconn, sub->slotname, opts.failover);
+			walrcv_alter_slot(wrconn, sub->slotname, opts.failover, opts.twophase);
 		}
 		PG_FINALLY();
 		{
@@ -1672,9 +1733,7 @@ DropSubscription(DropSubscriptionStmt *stmt, bool isTopLevel)
 	 * New workers won't be started because we hold an exclusive lock on the
 	 * subscription till the end of the transaction.
 	 */
-	LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
-	subworkers = logicalrep_workers_find(subid, false);
-	LWLockRelease(LogicalRepWorkerLock);
+	subworkers = logicalrep_workers_find(subid, false, true);
 	foreach(lc, subworkers)
 	{
 		LogicalRepWorker *w = (LogicalRepWorker *) lfirst(lc);
diff --git a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
index 02f12f2921..2f035a0c3c 100644
--- a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
+++ b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
@@ -80,7 +80,7 @@ static char *libpqrcv_create_slot(WalReceiverConn *conn,
 								  CRSSnapshotAction snapshot_action,
 								  XLogRecPtr *lsn);
 static void libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-								bool failover);
+								bool failover, bool two_phase);
 static pid_t libpqrcv_get_backend_pid(WalReceiverConn *conn);
 static WalRcvExecResult *libpqrcv_exec(WalReceiverConn *conn,
 									   const char *query,
@@ -1121,15 +1121,16 @@ libpqrcv_create_slot(WalReceiverConn *conn, const char *slotname,
  */
 static void
 libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-					bool failover)
+					bool failover, bool two_phase)
 {
 	StringInfoData cmd;
 	PGresult   *res;
 
 	initStringInfo(&cmd);
-	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( FAILOVER %s )",
+	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( FAILOVER %s, TWO_PHASE %s )",
 					 quote_identifier(slotname),
-					 failover ? "true" : "false");
+					 failover ? "true" : "false",
+					 two_phase ? "true" : "false");
 
 	res = libpqrcv_PQexec(conn->streamConn, cmd.data);
 	pfree(cmd.data);
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 27c3a91fb7..45744b771f 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -272,12 +272,15 @@ logicalrep_worker_find(Oid subid, Oid relid, bool only_running)
  * the subscription, instead of just one.
  */
 List *
-logicalrep_workers_find(Oid subid, bool only_running)
+logicalrep_workers_find(Oid subid, bool only_running, bool require_lock)
 {
 	int			i;
 	List	   *res = NIL;
 
-	Assert(LWLockHeldByMe(LogicalRepWorkerLock));
+	if (require_lock)
+		LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
+	else
+		Assert(LWLockHeldByMe(LogicalRepWorkerLock));
 
 	/* Search for attached worker for a given subscription id. */
 	for (i = 0; i < max_logical_replication_workers; i++)
@@ -288,6 +291,9 @@ logicalrep_workers_find(Oid subid, bool only_running)
 			res = lappend(res, w);
 	}
 
+	if (require_lock)
+		LWLockRelease(LogicalRepWorkerLock);
+
 	return res;
 }
 
@@ -759,7 +765,7 @@ logicalrep_worker_detach(void)
 
 		LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
 
-		workers = logicalrep_workers_find(MyLogicalRepWorker->subid, true);
+		workers = logicalrep_workers_find(MyLogicalRepWorker->subid, true, false);
 		foreach(lc, workers)
 		{
 			LogicalRepWorker *w = (LogicalRepWorker *) lfirst(lc);
diff --git a/src/backend/replication/logical/worker.c b/src/backend/replication/logical/worker.c
index 3b285894db..33bfeb1fb2 100644
--- a/src/backend/replication/logical/worker.c
+++ b/src/backend/replication/logical/worker.c
@@ -401,9 +401,6 @@ static void apply_handle_tuple_routing(ApplyExecutionData *edata,
 									   LogicalRepTupleData *newtup,
 									   CmdType operation);
 
-/* Compute GID for two_phase transactions */
-static void TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid, int szgid);
-
 /* Functions for skipping changes */
 static void maybe_start_skipping_changes(XLogRecPtr finish_lsn);
 static void stop_skipping_changes(void);
@@ -3911,7 +3908,7 @@ maybe_reread_subscription(void)
 	/* !slotname should never happen when enabled is true. */
 	Assert(newsub->slotname);
 
-	/* two-phase should not be altered */
+	/* two-phase cannot be altered while the worker exists */
 	Assert(newsub->twophasestate == MySubscription->twophasestate);
 
 	/*
@@ -4396,24 +4393,6 @@ cleanup_subxact_info()
 	subxact_data.nsubxacts_max = 0;
 }
 
-/*
- * Form the prepared transaction GID for two_phase transactions.
- *
- * Return the GID in the supplied buffer.
- */
-static void
-TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid, int szgid)
-{
-	Assert(subid != InvalidRepOriginId);
-
-	if (!TransactionIdIsValid(xid))
-		ereport(ERROR,
-				(errcode(ERRCODE_PROTOCOL_VIOLATION),
-				 errmsg_internal("invalid two-phase transaction ID")));
-
-	snprintf(gid, szgid, "pg_gid_%u_%u", subid, xid);
-}
-
 /*
  * Common function to run the apply loop with error handling. Disable the
  * subscription, if necessary.
@@ -5013,7 +4992,7 @@ AtEOXact_LogicalRepWorkers(bool isCommit)
 			List	   *workers;
 			ListCell   *lc2;
 
-			workers = logicalrep_workers_find(subid, true);
+			workers = logicalrep_workers_find(subid, true, false);
 			foreach(lc2, workers)
 			{
 				LogicalRepWorker *worker = (LogicalRepWorker *) lfirst(lc2);
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index baf9b89dc4..2ad6dca993 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -804,8 +804,10 @@ ReplicationSlotDrop(const char *name, bool nowait)
  * Change the definition of the slot identified by the specified name.
  */
 void
-ReplicationSlotAlter(const char *name, bool failover)
+ReplicationSlotAlter(const char *name, bool failover, bool two_phase)
 {
+	bool		update_slot = false;
+
 	Assert(MyReplicationSlot == NULL);
 
 	ReplicationSlotAcquire(name, false);
@@ -854,6 +856,20 @@ ReplicationSlotAlter(const char *name, bool failover)
 		MyReplicationSlot->data.failover = failover;
 		SpinLockRelease(&MyReplicationSlot->mutex);
 
+		update_slot = true;
+	}
+
+	if (MyReplicationSlot->data.two_phase != two_phase)
+	{
+		SpinLockAcquire(&MyReplicationSlot->mutex);
+		MyReplicationSlot->data.two_phase = two_phase;
+		SpinLockRelease(&MyReplicationSlot->mutex);
+
+		update_slot = true;
+	}
+
+	if (update_slot)
+	{
 		ReplicationSlotMarkDirty();
 		ReplicationSlotSave();
 	}
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 754f505c13..af776fccb8 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1409,9 +1409,11 @@ DropReplicationSlot(DropReplicationSlotCmd *cmd)
  * Process extra options given to ALTER_REPLICATION_SLOT.
  */
 static void
-ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd, bool *failover)
+ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd,
+						  bool *failover, bool *two_phase)
 {
 	bool		failover_given = false;
+	bool		two_phase_given = false;
 
 	/* Parse options */
 	foreach_ptr(DefElem, defel, cmd->options)
@@ -1425,6 +1427,15 @@ ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd, bool *failover)
 			failover_given = true;
 			*failover = defGetBoolean(defel);
 		}
+		else if (strcmp(defel->defname, "two_phase") == 0)
+		{
+			if (two_phase_given)
+				ereport(ERROR,
+						(errcode(ERRCODE_SYNTAX_ERROR),
+						 errmsg("conflicting or redundant options")));
+			two_phase_given = true;
+			*two_phase = defGetBoolean(defel);
+		}
 		else
 			elog(ERROR, "unrecognized option: %s", defel->defname);
 	}
@@ -1437,9 +1448,10 @@ static void
 AlterReplicationSlot(AlterReplicationSlotCmd *cmd)
 {
 	bool		failover = false;
+	bool		two_phase = false;
 
-	ParseAlterReplSlotOptions(cmd, &failover);
-	ReplicationSlotAlter(cmd->slotname, failover);
+	ParseAlterReplSlotOptions(cmd, &failover, &two_phase);
+	ReplicationSlotAlter(cmd->slotname, failover, two_phase);
 }
 
 /*
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
index d453e224d9..891face1b6 100644
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -1948,7 +1948,7 @@ psql_completion(const char *text, int start, int end)
 	else if (HeadMatches("ALTER", "SUBSCRIPTION", MatchAny) && TailMatches("SET", "("))
 		COMPLETE_WITH("binary", "disable_on_error", "failover", "origin",
 					  "password_required", "run_as_owner", "slot_name",
-					  "streaming", "synchronous_commit");
+					  "streaming", "synchronous_commit", "two_phase");
 	/* ALTER SUBSCRIPTION <name> SKIP ( */
 	else if (HeadMatches("ALTER", "SUBSCRIPTION", MatchAny) && TailMatches("SKIP", "("))
 		COMPLETE_WITH("lsn");
diff --git a/src/include/access/twophase.h b/src/include/access/twophase.h
index 56248c0006..d37e06fdee 100644
--- a/src/include/access/twophase.h
+++ b/src/include/access/twophase.h
@@ -62,4 +62,9 @@ extern void PrepareRedoRemove(TransactionId xid, bool giveWarning);
 extern void restoreTwoPhaseData(void);
 extern bool LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 						TimestampTz origin_prepare_timestamp);
+
+extern void TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid,
+								   int szgid);
+extern bool LookupGXactBySubid(Oid subid);
+
 #endif							/* TWOPHASE_H */
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index c9675ee87c..163a4a911a 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -243,7 +243,8 @@ extern void ReplicationSlotCreate(const char *name, bool db_specific,
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
 extern void ReplicationSlotDropAcquired(void);
-extern void ReplicationSlotAlter(const char *name, bool failover);
+extern void ReplicationSlotAlter(const char *name, bool failover,
+								 bool two_phase);
 
 extern void ReplicationSlotAcquire(const char *name, bool nowait);
 extern void ReplicationSlotRelease(void);
diff --git a/src/include/replication/walreceiver.h b/src/include/replication/walreceiver.h
index 12f71fa99b..31fa1257ec 100644
--- a/src/include/replication/walreceiver.h
+++ b/src/include/replication/walreceiver.h
@@ -372,12 +372,13 @@ typedef char *(*walrcv_create_slot_fn) (WalReceiverConn *conn,
 /*
  * walrcv_alter_slot_fn
  *
- * Change the definition of a replication slot. Currently, it only supports
- * changing the failover property of the slot.
+ * Change the definition of a replication slot. Currently, it supports
+ * changing the failover and the two_phase property of the slot.
  */
 typedef void (*walrcv_alter_slot_fn) (WalReceiverConn *conn,
 									  const char *slotname,
-									  bool failover);
+									  bool failover,
+									  bool two_phase);
 
 /*
  * walrcv_get_backend_pid_fn
@@ -455,8 +456,8 @@ extern PGDLLIMPORT WalReceiverFunctionsType *WalReceiverFunctions;
 	WalReceiverFunctions->walrcv_send(conn, buffer, nbytes)
 #define walrcv_create_slot(conn, slotname, temporary, two_phase, failover, snapshot_action, lsn) \
 	WalReceiverFunctions->walrcv_create_slot(conn, slotname, temporary, two_phase, failover, snapshot_action, lsn)
-#define walrcv_alter_slot(conn, slotname, failover) \
-	WalReceiverFunctions->walrcv_alter_slot(conn, slotname, failover)
+#define walrcv_alter_slot(conn, slotname, failover, two_phase) \
+	WalReceiverFunctions->walrcv_alter_slot(conn, slotname, failover, two_phase)
 #define walrcv_get_backend_pid(conn) \
 	WalReceiverFunctions->walrcv_get_backend_pid(conn)
 #define walrcv_exec(conn, exec, nRetTypes, retTypes) \
diff --git a/src/include/replication/worker_internal.h b/src/include/replication/worker_internal.h
index 515aefd519..990f5242f9 100644
--- a/src/include/replication/worker_internal.h
+++ b/src/include/replication/worker_internal.h
@@ -240,7 +240,8 @@ extern PGDLLIMPORT bool InitializingApplyWorker;
 extern void logicalrep_worker_attach(int slot);
 extern LogicalRepWorker *logicalrep_worker_find(Oid subid, Oid relid,
 												bool only_running);
-extern List *logicalrep_workers_find(Oid subid, bool only_running);
+extern List *logicalrep_workers_find(Oid subid, bool only_running,
+									 bool require_lock);
 extern bool logicalrep_worker_launch(LogicalRepWorkerType wtype,
 									 Oid dbid, Oid subid, const char *subname,
 									 Oid userid, Oid relid,
diff --git a/src/test/regress/expected/subscription.out b/src/test/regress/expected/subscription.out
index 0f2a25cdc1..51fa4b9690 100644
--- a/src/test/regress/expected/subscription.out
+++ b/src/test/regress/expected/subscription.out
@@ -377,10 +377,7 @@ HINT:  To initiate replication, you must manually create the replication slot, e
  regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | p                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
---fail - alter of two_phase option not supported.
-ALTER SUBSCRIPTION regress_testsub SET (two_phase = false);
-ERROR:  unrecognized subscription parameter: "two_phase"
--- but can alter streaming when two_phase enabled
+-- We can alter streaming when two_phase enabled
 ALTER SUBSCRIPTION regress_testsub SET (streaming = true);
 \dRs+
                                                                                                                 List of subscriptions
diff --git a/src/test/regress/sql/subscription.sql b/src/test/regress/sql/subscription.sql
index 3e5ba4cb8c..a3886d79ca 100644
--- a/src/test/regress/sql/subscription.sql
+++ b/src/test/regress/sql/subscription.sql
@@ -256,10 +256,7 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUBLICATION testpub WITH (connect = false, two_phase = true);
 
 \dRs+
---fail - alter of two_phase option not supported.
-ALTER SUBSCRIPTION regress_testsub SET (two_phase = false);
-
--- but can alter streaming when two_phase enabled
+-- We can alter streaming when two_phase enabled
 ALTER SUBSCRIPTION regress_testsub SET (streaming = true);
 
 \dRs+
diff --git a/src/test/subscription/t/021_twophase.pl b/src/test/subscription/t/021_twophase.pl
index 9437cd4c3b..4e8f627f7b 100644
--- a/src/test/subscription/t/021_twophase.pl
+++ b/src/test/subscription/t/021_twophase.pl
@@ -367,6 +367,81 @@ $result =
   $node_subscriber->safe_psql('postgres', "SELECT count(*) FROM tab_copy;");
 is($result, qq(2), 'replicated data in subscriber table');
 
+# Clean up
+$node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub");
+
+###############################
+# Disable the subscription and alter it to two_phase = false,
+# then verify that the altered subscription reflects the two_phase option.
+###############################
+
+# Alter subscription two_phase to false
+$node_subscriber->safe_psql('postgres',
+    "ALTER SUBSCRIPTION tap_sub_copy DISABLE;");
+$node_subscriber->poll_query_until('postgres',
+    "SELECT count(*) = 0 FROM pg_stat_activity WHERE backend_type = 'logical replication worker'"
+);
+$node_subscriber->safe_psql(
+	'postgres', "
+    ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = false);
+    ALTER SUBSCRIPTION tap_sub_copy ENABLE;");
+
+# Wait for subscription startup
+$node_subscriber->wait_for_subscription_sync($node_publisher, $appname_copy);
+
+# Make sure that the two-phase is disabled on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT subtwophasestate FROM pg_subscription WHERE subname = 'tap_sub_copy';"
+);
+is($result, qq(d), 'two-phase should be disabled');
+
+# Now do a prepare on the publisher and make sure that it is not replicated.
+$node_publisher->safe_psql(
+	'postgres', qq{
+    BEGIN;
+    INSERT INTO tab_copy VALUES (100);
+    PREPARE TRANSACTION 'newgid';
+	});
+
+# Wait for the subscriber to catchup
+$node_publisher->wait_for_catchup($appname_copy);
+
+# Make sure there are no prepared transactions on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT count(*) FROM pg_prepared_xacts;");
+is($result, qq(0), 'should be no prepared transactions on subscriber');
+
+# Now commit the insert and verify that it is replicated
+$node_publisher->safe_psql('postgres', "COMMIT PREPARED 'newgid';");
+
+# Wait for the subscriber to catchup
+$node_publisher->wait_for_catchup($appname_copy);
+
+# Make sure that the committed transaction is replicated.
+$result =
+  $node_subscriber->safe_psql('postgres', "SELECT count(*) FROM tab_copy;");
+is($result, qq(3), 'replicated data in subscriber table');
+
+# Alter subscription two_phase to true
+$node_subscriber->safe_psql('postgres',
+    "ALTER SUBSCRIPTION tap_sub_copy DISABLE;");
+$node_subscriber->poll_query_until('postgres',
+    "SELECT count(*) = 0 FROM pg_stat_activity WHERE backend_type = 'logical replication worker'"
+);
+$node_subscriber->safe_psql(
+	'postgres', "
+    ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = true);
+    ALTER SUBSCRIPTION tap_sub_copy ENABLE;");
+
+# Wait for subscription startup
+$node_subscriber->wait_for_subscription_sync($node_publisher, $appname_copy);
+
+# Make sure that the two-phase is enabled on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT subtwophasestate FROM pg_subscription WHERE subname = 'tap_sub_copy';"
+);
+is($result, qq(e), 'two-phase should be enabled');
+
 $node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub_copy;");
 $node_publisher->safe_psql('postgres', "DROP PUBLICATION tap_pub_copy;");
 
@@ -374,8 +449,6 @@ $node_publisher->safe_psql('postgres', "DROP PUBLICATION tap_pub_copy;");
 # check all the cleanup
 ###############################
 
-$node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub");
-
 $result = $node_subscriber->safe_psql('postgres',
 	"SELECT count(*) FROM pg_subscription");
 is($result, qq(0), 'check subscription was dropped on subscriber');
-- 
2.43.0

From e4fe6cde1f4a123668b0a2c1396526bee816c536 Mon Sep 17 00:00:00 2001
From: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Date: Wed, 17 Apr 2024 06:18:23 +0000
Subject: [PATCH v17 2/3] Alter slot option two_phase only when altering "true"
 to "false"

Since the two_phase option is controlled by both the publisher (as a slot option)
and the subscriber (as a subscription option), the slot option must also be
modified.

Regarding the false->true case, the backend process alters the subtwophase to
LOGICALREP_TWOPHASE_STATE_PENDING once. After the subscription is enabled, a new
logical replication worker requests to change the two_phase option of its slot
from pending to true after the initial data synchronization is done. The code
path is the same as the case in which two_phase is initially set to true, so
there is no need to do something remarkable. However, for the true->false case,
the backend must connect to the publisher and expressly change the parameter
because the apply worker does not alter the option to false. Because this
operation cannot be rolled back, altering the two_phase parameter from "true"
to "false" within a transaction is prohibited.
---
 doc/src/sgml/ref/alter_subscription.sgml      |  2 +-
 src/backend/commands/subscriptioncmds.c       | 76 ++++++++++++++-----
 .../libpqwalreceiver/libpqwalreceiver.c       | 23 ++++--
 src/include/replication/walreceiver.h         |  5 +-
 src/test/subscription/t/021_twophase.pl       | 41 ++++++----
 5 files changed, 102 insertions(+), 45 deletions(-)

diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index 0b23df1b77..475a42a2e3 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -70,7 +70,7 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
    <command>ALTER SUBSCRIPTION ... {SET|ADD|DROP} PUBLICATION ...</command>
    with <literal>refresh</literal> option as <literal>true</literal>,
    <command>ALTER SUBSCRIPTION ... SET (failover = true|false)</command> and
-   <command>ALTER SUBSCRIPTION ... SET (two_phase = true|false)</command>
+   <command>ALTER SUBSCRIPTION ... SET (two_phase = off)</command>
    cannot be executed inside a transaction block.
 
    These commands also cannot be executed when the subscription has
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index 255628c396..d109fb2e84 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -112,6 +112,7 @@ static List *merge_publications(List *oldpublist, List *newpublist, bool addpub,
 static void ReportSlotConnectionError(List *rstates, Oid subid, char *slotname, char *err);
 static void CommonChecksForFailoverAndTwophase(Subscription *sub,
 											   const char *option,
+											   bool needs_update,
 											   bool isTopLevel);
 
 
@@ -1074,11 +1075,9 @@ AlterSubscription_refresh(Subscription *sub, bool copy_data,
  */
 static void
 CommonChecksForFailoverAndTwophase(Subscription *sub, const char *option,
-								   bool isTopLevel)
+								   bool needs_update, bool isTopLevel)
 {
-	StringInfoData cmd;
-
-	if (!sub->slotname)
+	if (needs_update && !sub->slotname)
 		ereport(ERROR,
 				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
 				 errmsg("cannot set %s for a subscription that does not have a slot name",
@@ -1096,16 +1095,20 @@ CommonChecksForFailoverAndTwophase(Subscription *sub, const char *option,
 				 errmsg("cannot set %s for enabled subscription",
 						option)));
 
-	initStringInfo(&cmd);
-	appendStringInfo(&cmd, "ALTER SUBSCRIPTION ... SET (%s)", option);
-
 	/*
 	 * The changed option of the slot can't be rolled back: prevent we are in
 	 * the transaction state.
 	 */
-	PreventInTransactionBlock(isTopLevel, cmd.data);
+	if (needs_update)
+	{
+		StringInfoData cmd;
 
-	pfree(cmd.data);
+		initStringInfo(&cmd);
+		appendStringInfo(&cmd, "ALTER SUBSCRIPTION ... SET (%s)", option);
+
+		PreventInTransactionBlock(isTopLevel, cmd.data);
+		pfree(cmd.data);
+	}
 }
 
 /*
@@ -1127,6 +1130,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 	Form_pg_subscription form;
 	bits32		supported_opts;
 	SubOpts		opts = {0};
+	bool		update_failover = false;
+	bool		update_two_phase = false;
 
 	rel = table_open(SubscriptionRelationId, RowExclusiveLock);
 
@@ -1259,8 +1264,16 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 
 				if (IsSet(opts.specified_opts, SUBOPT_FAILOVER))
 				{
+					/*
+					 * First mark the needs to alter the replication slot.
+					 * Failover option is controlled by both the publisher (as
+					 * a slot option) and the subscriber (as a subscription
+					 * option).
+					 */
+					update_failover = true;
+
 					CommonChecksForFailoverAndTwophase(sub, "failover",
-													   isTopLevel);
+													   update_failover, isTopLevel);
 
 					values[Anum_pg_subscription_subfailover - 1] =
 						BoolGetDatum(opts.failover);
@@ -1269,16 +1282,36 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 
 				if (IsSet(opts.specified_opts, SUBOPT_TWOPHASE_COMMIT))
 				{
+					/*
+					 * First check the need to alter the replication slot.
+					 * Two_phase option is controlled by both the publisher
+					 * (as a slot option) and the subscriber (as a
+					 * subscription option). The slot option must be altered
+					 * only when changing "true" to "false".
+					 *
+					 * There is no need to do something remarkable regarding
+					 * the "false" to "true" case; the backend process alters
+					 * subtwophase to LOGICALREP_TWOPHASE_STATE_PENDING once.
+					 * After the subscription is enabled, a new logical
+					 * replication worker requests to change the two_phase
+					 * option of its slot from pending to true when the
+					 * initial data synchronization is done. The code path is
+					 * the same as the case in which two_phase is initially
+					 * set to true.
+					 */
+					update_two_phase = !opts.twophase;
+
 					CommonChecksForFailoverAndTwophase(sub, "two_phase",
-													   isTopLevel);
+													   update_two_phase, isTopLevel);
 
 					/*
-					 * slot_name and two_phase cannot be altered
-					 * simultaneously. The latter part refers to the pre-set
-					 * slot name and tries to modify the slot option, so
-					 * changing both does not make sense.
+					 * If the wo_phase slot option must be altered, this cannot
+					 * be altered with slot_name simultaneously. The latter
+					 * part refers to the pre-set slot name and tries to modify
+					 * the slot option, so changing both does not make sense.
 					 */
-					if (IsSet(opts.specified_opts, SUBOPT_SLOT_NAME))
+					if (update_two_phase &&
+						IsSet(opts.specified_opts, SUBOPT_SLOT_NAME))
 						ereport(ERROR,
 								(errcode(ERRCODE_SYNTAX_ERROR),
 						 		 errmsg("slot_name and two_phase cannot be altered at the same time")));
@@ -1300,7 +1333,7 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 					 * two_phase cannot be disabled if there are any
 					 * uncommitted prepared transactions present.
 					 */
-					if (!opts.twophase &&
+					if (update_two_phase &&
 						sub->twophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
 						LookupGXactBySubid(subid))
 						ereport(ERROR,
@@ -1559,14 +1592,13 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 	}
 
 	/*
-	 * Try to acquire the connection necessary for altering slot.
+	 * Try to acquire the connection necessary for altering slot, if needed.
 	 *
 	 * This has to be at the end because otherwise if there is an error while
 	 * doing the database operations we won't be able to rollback altered
 	 * slot.
 	 */
-	if (replaces[Anum_pg_subscription_subfailover - 1] ||
-		replaces[Anum_pg_subscription_subtwophasestate - 1])
+	if (update_failover || update_two_phase)
 	{
 		bool		must_use_password;
 		char	   *err;
@@ -1586,7 +1618,9 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 
 		PG_TRY();
 		{
-			walrcv_alter_slot(wrconn, sub->slotname, opts.failover, opts.twophase);
+			walrcv_alter_slot(wrconn, sub->slotname,
+							  update_failover ? &opts.failover : NULL,
+							  update_two_phase ? &opts.twophase : NULL);
 		}
 		PG_FINALLY();
 		{
diff --git a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
index 2f035a0c3c..07dfec947d 100644
--- a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
+++ b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
@@ -80,7 +80,7 @@ static char *libpqrcv_create_slot(WalReceiverConn *conn,
 								  CRSSnapshotAction snapshot_action,
 								  XLogRecPtr *lsn);
 static void libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-								bool failover, bool two_phase);
+								const bool *failover, const bool *two_phase);
 static pid_t libpqrcv_get_backend_pid(WalReceiverConn *conn);
 static WalRcvExecResult *libpqrcv_exec(WalReceiverConn *conn,
 									   const char *query,
@@ -1121,16 +1121,27 @@ libpqrcv_create_slot(WalReceiverConn *conn, const char *slotname,
  */
 static void
 libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-					bool failover, bool two_phase)
+					const bool *failover, const bool *two_phase)
 {
 	StringInfoData cmd;
 	PGresult   *res;
 
 	initStringInfo(&cmd);
-	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( FAILOVER %s, TWO_PHASE %s )",
-					 quote_identifier(slotname),
-					 failover ? "true" : "false",
-					 two_phase ? "true" : "false");
+	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( ",
+					 quote_identifier(slotname));
+
+	if (failover)
+		appendStringInfo(&cmd, "FAILOVER %s",
+						 *failover ? "true" : "false");
+
+	if (failover && two_phase)
+		appendStringInfo(&cmd, ", ");
+
+	if (two_phase)
+		appendStringInfo(&cmd, "TWO_PHASE %s",
+						 *two_phase ? "true" : "false");
+
+	appendStringInfoString(&cmd, " );");
 
 	res = libpqrcv_PQexec(conn->streamConn, cmd.data);
 	pfree(cmd.data);
diff --git a/src/include/replication/walreceiver.h b/src/include/replication/walreceiver.h
index 31fa1257ec..7ffa5a58b3 100644
--- a/src/include/replication/walreceiver.h
+++ b/src/include/replication/walreceiver.h
@@ -377,8 +377,9 @@ typedef char *(*walrcv_create_slot_fn) (WalReceiverConn *conn,
  */
 typedef void (*walrcv_alter_slot_fn) (WalReceiverConn *conn,
 									  const char *slotname,
-									  bool failover,
-									  bool two_phase);
+									  const bool *failover,
+									  const bool *two_phase);
+
 
 /*
  * walrcv_get_backend_pid_fn
diff --git a/src/test/subscription/t/021_twophase.pl b/src/test/subscription/t/021_twophase.pl
index 4e8f627f7b..f56dff4b12 100644
--- a/src/test/subscription/t/021_twophase.pl
+++ b/src/test/subscription/t/021_twophase.pl
@@ -375,6 +375,12 @@ $node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub");
 # then verify that the altered subscription reflects the two_phase option.
 ###############################
 
+# Confirm two-phase slot option is enabled before altering
+$result = $node_publisher->safe_psql('postgres',
+	"SELECT two_phase FROM pg_replication_slots WHERE slot_name = 'tap_sub_copy';"
+);
+is($result, qq(t), 'two-phase is enabled');
+
 # Alter subscription two_phase to false
 $node_subscriber->safe_psql('postgres',
     "ALTER SUBSCRIPTION tap_sub_copy DISABLE;");
@@ -393,7 +399,13 @@ $node_subscriber->wait_for_subscription_sync($node_publisher, $appname_copy);
 $result = $node_subscriber->safe_psql('postgres',
 	"SELECT subtwophasestate FROM pg_subscription WHERE subname = 'tap_sub_copy';"
 );
-is($result, qq(d), 'two-phase should be disabled');
+is($result, qq(d), 'two-phase subscription option should be disabled');
+
+# Make sure that the two-phase slot option is also disabled
+$result = $node_publisher->safe_psql('postgres',
+	"SELECT two_phase FROM pg_replication_slots WHERE slot_name = 'tap_sub_copy';"
+);
+is($result, qq(f), 'two-phase slot option should be disabled');
 
 # Now do a prepare on the publisher and make sure that it is not replicated.
 $node_publisher->safe_psql(
@@ -411,6 +423,19 @@ $result = $node_subscriber->safe_psql('postgres',
 	"SELECT count(*) FROM pg_prepared_xacts;");
 is($result, qq(0), 'should be no prepared transactions on subscriber');
 
+# Toggle the two_phase to "true" *before* the COMMIT PREPARED. Since we are the
+# special path for the case where both two_phase and failover are altered, it
+# is also set to "true".
+$node_subscriber->safe_psql('postgres',
+    "ALTER SUBSCRIPTION tap_sub_copy DISABLE;");
+$node_subscriber->poll_query_until('postgres',
+    "SELECT count(*) = 0 FROM pg_stat_activity WHERE backend_type = 'logical replication worker'"
+);
+$node_subscriber->safe_psql(
+	'postgres', "
+    ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = true, failover = true);
+    ALTER SUBSCRIPTION tap_sub_copy ENABLE;");
+
 # Now commit the insert and verify that it is replicated
 $node_publisher->safe_psql('postgres', "COMMIT PREPARED 'newgid';");
 
@@ -422,20 +447,6 @@ $result =
   $node_subscriber->safe_psql('postgres', "SELECT count(*) FROM tab_copy;");
 is($result, qq(3), 'replicated data in subscriber table');
 
-# Alter subscription two_phase to true
-$node_subscriber->safe_psql('postgres',
-    "ALTER SUBSCRIPTION tap_sub_copy DISABLE;");
-$node_subscriber->poll_query_until('postgres',
-    "SELECT count(*) = 0 FROM pg_stat_activity WHERE backend_type = 'logical replication worker'"
-);
-$node_subscriber->safe_psql(
-	'postgres', "
-    ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = true);
-    ALTER SUBSCRIPTION tap_sub_copy ENABLE;");
-
-# Wait for subscription startup
-$node_subscriber->wait_for_subscription_sync($node_publisher, $appname_copy);
-
 # Make sure that the two-phase is enabled on the subscriber
 $result = $node_subscriber->safe_psql('postgres',
 	"SELECT subtwophasestate FROM pg_subscription WHERE subname = 'tap_sub_copy';"
-- 
2.43.0

From a2a93925c9e05ea82739cb16dc7bd06582099f11 Mon Sep 17 00:00:00 2001
From: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Date: Tue, 9 Jul 2024 08:01:43 +0000
Subject: [PATCH v17 3/3] Notify users to roll back prepared transactions

---
 doc/src/sgml/ref/alter_subscription.sgml | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index 475a42a2e3..5263fe7c68 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -233,8 +233,6 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>, and
       <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>.
       Only a superuser can set <literal>password_required = false</literal>.
-      The <literal>two_phase</literal> parameter can only be altered when the
-      subscription is disabled.
      </para>
 
      <para>
@@ -256,6 +254,19 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>
       option is enabled.
      </para>
+
+     <para>
+      The <literal>two_phase</literal> parameter can only be altered when the
+      subscription is disabled. When altering the parameter from <literal>true</literal>
+      to <literal>false</literal>, the backend process checks for any incomplete
+      prepared transactions done by the logical replication worker (from when
+      <literal>two_phase</literal> parameter was still <literal>true</literal>)
+      and, if any are found, this command is failed with an error. In this
+      case, you can resolve prepared transactions on the publisher node or
+      manually roll back them on the subscriber. Alter the altering from
+      <literal>true</literal> to <literal>false</literal>, the publisher will
+      replicate transactions again when they are committed.
+     </para>
     </listitem>
    </varlistentry>
 
-- 
2.43.0

From 3bbaaba53a0cb3db43cc893acbd3ffbedd61bff1 Mon Sep 17 00:00:00 2001
From: Hou Zhijie <houzj.fnst@cn.fujitsu.com>
Date: Sat, 13 Jul 2024 18:31:28 +0800
Subject: [PATCH] fix alter replication slot

---
 doc/src/sgml/protocol.sgml              | 16 ++++++++++++++
 src/backend/commands/subscriptioncmds.c |  2 +-
 src/backend/replication/slot.c          | 16 ++++++++------
 src/backend/replication/walsender.c     | 29 +++++++++++++++----------
 src/include/replication/slot.h          |  4 ++--
 5 files changed, 46 insertions(+), 21 deletions(-)

diff --git a/doc/src/sgml/protocol.sgml b/doc/src/sgml/protocol.sgml
index 1b27d0a547..3ac4a4be28 100644
--- a/doc/src/sgml/protocol.sgml
+++ b/doc/src/sgml/protocol.sgml
@@ -2206,6 +2206,22 @@ psql "dbname=postgres replication=database" -c "IDENTIFY_SYSTEM;"
        </varlistentry>
       </variablelist>
 
+      <variablelist>
+       <varlistentry>
+        <term><literal>TWO_PHASE [ <replaceable class="parameter">boolean</replaceable> ]</literal></term>
+        <listitem>
+         <para>
+          If true, this logical replication slot supports decoding of two-phase
+          commit. With this option, commands related to two-phase commit such as
+          <literal>PREPARE TRANSACTION</literal>, <literal>COMMIT PREPARED</literal>
+          and <literal>ROLLBACK PREPARED</literal> are decoded and transmitted.
+          The transaction will be decoded and transmitted at
+          <literal>PREPARE TRANSACTION</literal> time.
+         </para>
+        </listitem>
+       </varlistentry>
+      </variablelist>
+
      </listitem>
     </varlistentry>
 
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index 7604e228e8..c48b6d0549 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -1308,7 +1308,7 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 						ereport(ERROR,
 								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
 								 errmsg("cannot disable two_phase when uncommitted prepared transactions present"),
-								 errhint("Resolve these transactions and try again")));
+								 errhint("Resolve these transactions and try again.")));
 
 					/* Change system catalog acoordingly */
 					values[Anum_pg_subscription_subtwophasestate - 1] =
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 2ad6dca993..2f167a2adc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -804,11 +804,12 @@ ReplicationSlotDrop(const char *name, bool nowait)
  * Change the definition of the slot identified by the specified name.
  */
 void
-ReplicationSlotAlter(const char *name, bool failover, bool two_phase)
+ReplicationSlotAlter(const char *name, bool *failover, bool *two_phase)
 {
 	bool		update_slot = false;
 
 	Assert(MyReplicationSlot == NULL);
+	Assert(failover || two_phase);
 
 	ReplicationSlotAcquire(name, false);
 
@@ -834,7 +835,7 @@ ReplicationSlotAlter(const char *name, bool failover, bool two_phase)
 		 * Do not allow users to enable failover on the standby as we do not
 		 * support sync to the cascading standby.
 		 */
-		if (failover)
+		if (failover && *failover)
 			ereport(ERROR,
 					errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 					errmsg("cannot enable failover for a replication slot"
@@ -845,24 +846,25 @@ ReplicationSlotAlter(const char *name, bool failover, bool two_phase)
 	 * Do not allow users to enable failover for temporary slots as we do not
 	 * support syncing temporary slots to the standby.
 	 */
-	if (failover && MyReplicationSlot->data.persistency == RS_TEMPORARY)
+	if (failover && *failover &&
+		MyReplicationSlot->data.persistency == RS_TEMPORARY)
 		ereport(ERROR,
 				errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 				errmsg("cannot enable failover for a temporary replication slot"));
 
-	if (MyReplicationSlot->data.failover != failover)
+	if (failover && MyReplicationSlot->data.failover != *failover)
 	{
 		SpinLockAcquire(&MyReplicationSlot->mutex);
-		MyReplicationSlot->data.failover = failover;
+		MyReplicationSlot->data.failover = *failover;
 		SpinLockRelease(&MyReplicationSlot->mutex);
 
 		update_slot = true;
 	}
 
-	if (MyReplicationSlot->data.two_phase != two_phase)
+	if (two_phase && MyReplicationSlot->data.two_phase != *two_phase)
 	{
 		SpinLockAcquire(&MyReplicationSlot->mutex);
-		MyReplicationSlot->data.two_phase = two_phase;
+		MyReplicationSlot->data.two_phase = *two_phase;
 		SpinLockRelease(&MyReplicationSlot->mutex);
 
 		update_slot = true;
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 5224ea6c2c..f3b5068d95 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1411,30 +1411,31 @@ DropReplicationSlot(DropReplicationSlotCmd *cmd)
  */
 static void
 ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd,
-						  bool *failover, bool *two_phase)
+						  bool *failover_given, bool *failover,
+						  bool *two_phase_given, bool *two_phase)
 {
-	bool		failover_given = false;
-	bool		two_phase_given = false;
+	*failover_given = false;
+	*two_phase_given = false;
 
 	/* Parse options */
 	foreach_ptr(DefElem, defel, cmd->options)
 	{
 		if (strcmp(defel->defname, "failover") == 0)
 		{
-			if (failover_given)
+			if (*failover_given)
 				ereport(ERROR,
 						(errcode(ERRCODE_SYNTAX_ERROR),
 						 errmsg("conflicting or redundant options")));
-			failover_given = true;
+			*failover_given = true;
 			*failover = defGetBoolean(defel);
 		}
 		else if (strcmp(defel->defname, "two_phase") == 0)
 		{
-			if (two_phase_given)
+			if (*two_phase_given)
 				ereport(ERROR,
 						(errcode(ERRCODE_SYNTAX_ERROR),
 						 errmsg("conflicting or redundant options")));
-			two_phase_given = true;
+			*two_phase_given = true;
 			*two_phase = defGetBoolean(defel);
 		}
 		else
@@ -1448,11 +1449,17 @@ ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd,
 static void
 AlterReplicationSlot(AlterReplicationSlotCmd *cmd)
 {
-	bool		failover = false;
-	bool		two_phase = false;
+	bool		failover_given;
+	bool		two_phase_given;
+	bool		failover;
+	bool		two_phase;
+
+	ParseAlterReplSlotOptions(cmd, &failover_given, &failover,
+							  &two_phase_given, &two_phase);
 
-	ParseAlterReplSlotOptions(cmd, &failover, &two_phase);
-	ReplicationSlotAlter(cmd->slotname, failover, two_phase);
+	ReplicationSlotAlter(cmd->slotname,
+						 failover_given ? &failover : NULL,
+						 two_phase_given ? &two_phase : NULL);
 }
 
 /*
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 163a4a911a..cde164472a 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -243,8 +243,8 @@ extern void ReplicationSlotCreate(const char *name, bool db_specific,
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
 extern void ReplicationSlotDropAcquired(void);
-extern void ReplicationSlotAlter(const char *name, bool failover,
-								 bool two_phase);
+extern void ReplicationSlotAlter(const char *name, bool *failover,
+								 bool *two_phase);
 
 extern void ReplicationSlotAcquire(const char *name, bool nowait);
 extern void ReplicationSlotRelease(void);
-- 
2.30.0.windows.2

From e7a2051d90b236989707d33236f0ab840c982283 Mon Sep 17 00:00:00 2001
From: Ajin Cherian <ajinc@fast.au.fujitsu.com>
Date: Fri, 5 Apr 2024 06:47:18 -0400
Subject: [PATCH v18 1/3] Allow altering of two_phase option of a SUBSCRIPTION

This patch allows the user to alter the 'two_phase' option of a subscriber provided no
uncommitted prepared transactions are pending on that subscription.

Author: Cherian Ajin, Hayato Kuroda
---
 doc/src/sgml/protocol.sgml                    |  16 +++
 doc/src/sgml/ref/alter_subscription.sgml      |  12 +-
 src/backend/access/transam/twophase.c         |  62 +++++++++
 src/backend/commands/subscriptioncmds.c       | 131 +++++++++++++-----
 .../libpqwalreceiver/libpqwalreceiver.c       |   9 +-
 src/backend/replication/logical/launcher.c    |  12 +-
 src/backend/replication/logical/worker.c      |  25 +---
 src/backend/replication/slot.c                |  28 +++-
 src/backend/replication/walsender.c           |  33 ++++-
 src/bin/psql/tab-complete.c                   |   2 +-
 src/include/access/twophase.h                 |   5 +
 src/include/replication/slot.h                |   3 +-
 src/include/replication/walreceiver.h         |  11 +-
 src/include/replication/worker_internal.h     |   3 +-
 src/test/regress/expected/subscription.out    |   5 +-
 src/test/regress/sql/subscription.sql         |   5 +-
 src/test/subscription/t/021_twophase.pl       |  77 +++++++++-
 17 files changed, 337 insertions(+), 102 deletions(-)

diff --git a/doc/src/sgml/protocol.sgml b/doc/src/sgml/protocol.sgml
index 1b27d0a547..3ac4a4be28 100644
--- a/doc/src/sgml/protocol.sgml
+++ b/doc/src/sgml/protocol.sgml
@@ -2206,6 +2206,22 @@ psql "dbname=postgres replication=database" -c "IDENTIFY_SYSTEM;"
        </varlistentry>
       </variablelist>
 
+      <variablelist>
+       <varlistentry>
+        <term><literal>TWO_PHASE [ <replaceable class="parameter">boolean</replaceable> ]</literal></term>
+        <listitem>
+         <para>
+          If true, this logical replication slot supports decoding of two-phase
+          commit. With this option, commands related to two-phase commit such as
+          <literal>PREPARE TRANSACTION</literal>, <literal>COMMIT PREPARED</literal>
+          and <literal>ROLLBACK PREPARED</literal> are decoded and transmitted.
+          The transaction will be decoded and transmitted at
+          <literal>PREPARE TRANSACTION</literal> time.
+         </para>
+        </listitem>
+       </varlistentry>
+      </variablelist>
+
      </listitem>
     </varlistentry>
 
diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index 476f195622..0b23df1b77 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -68,8 +68,9 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
   <para>
    Commands <command>ALTER SUBSCRIPTION ... REFRESH PUBLICATION</command>,
    <command>ALTER SUBSCRIPTION ... {SET|ADD|DROP} PUBLICATION ...</command>
-   with <literal>refresh</literal> option as <literal>true</literal> and
-   <command>ALTER SUBSCRIPTION ... SET (failover = true|false)</command>
+   with <literal>refresh</literal> option as <literal>true</literal>,
+   <command>ALTER SUBSCRIPTION ... SET (failover = true|false)</command> and
+   <command>ALTER SUBSCRIPTION ... SET (two_phase = true|false)</command>
    cannot be executed inside a transaction block.
 
    These commands also cannot be executed when the subscription has
@@ -228,9 +229,12 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-disable-on-error"><literal>disable_on_error</literal></link>,
       <link linkend="sql-createsubscription-params-with-password-required"><literal>password_required</literal></link>,
       <link linkend="sql-createsubscription-params-with-run-as-owner"><literal>run_as_owner</literal></link>,
-      <link linkend="sql-createsubscription-params-with-origin"><literal>origin</literal></link>, and
-      <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>.
+      <link linkend="sql-createsubscription-params-with-origin"><literal>origin</literal></link>,
+      <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>, and
+      <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>.
       Only a superuser can set <literal>password_required = false</literal>.
+      The <literal>two_phase</literal> parameter can only be altered when the
+      subscription is disabled.
      </para>
 
      <para>
diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index 9a8257fcaf..35bce6809d 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -2681,3 +2681,65 @@ LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 	LWLockRelease(TwoPhaseStateLock);
 	return found;
 }
+
+/*
+ * TwoPhaseTransactionGid
+ *		Form the prepared transaction GID for two_phase transactions.
+ *
+ * Return the GID in the supplied buffer.
+ */
+void
+TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid, int szgid)
+{
+	Assert(subid != InvalidRepOriginId);
+
+	if (!TransactionIdIsValid(xid))
+		ereport(ERROR,
+				(errcode(ERRCODE_PROTOCOL_VIOLATION),
+				 errmsg_internal("invalid two-phase transaction ID")));
+
+	snprintf(gid, szgid, "pg_gid_%u_%u", subid, xid);
+}
+
+/*
+ * IsTwoPhaseTransactionGidForSubid
+ *		Check whether the given GID (as formed by TwoPhaseTransactionGid) is
+ *		for the specified 'subid'.
+ */
+static bool
+IsTwoPhaseTransactionGidForSubid(Oid subid, char *gid)
+{
+	int			ret;
+	Oid			subid_written;
+	TransactionId xid;
+
+	ret = sscanf(gid, "pg_gid_%u_%u", &subid_written, &xid);
+
+	return (ret == 2 && subid == subid_written);
+}
+
+/*
+ * LookupGXactBySubid
+ *		Check if the prepared transaction done by apply worker exists.
+ */
+bool
+LookupGXactBySubid(Oid subid)
+{
+	bool		found = false;
+
+	LWLockAcquire(TwoPhaseStateLock, LW_SHARED);
+	for (int i = 0; i < TwoPhaseState->numPrepXacts; i++)
+	{
+		GlobalTransaction gxact = TwoPhaseState->prepXacts[i];
+
+		/* Ignore not-yet-valid GIDs. */
+		if (gxact->valid &&
+			IsTwoPhaseTransactionGidForSubid(subid, gxact->gid))
+		{
+			found = true;
+			break;
+		}
+	}
+	LWLockRelease(TwoPhaseStateLock);
+	return found;
+}
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index 16d83b3253..d7e2b141b3 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -16,6 +16,7 @@
 
 #include "access/htup_details.h"
 #include "access/table.h"
+#include "access/twophase.h"
 #include "access/xact.h"
 #include "catalog/catalog.h"
 #include "catalog/dependency.h"
@@ -109,6 +110,8 @@ static void check_publications_origin(WalReceiverConn *wrconn,
 static void check_duplicates_in_publist(List *publist, Datum *datums);
 static List *merge_publications(List *oldpublist, List *newpublist, bool addpub, const char *subname);
 static void ReportSlotConnectionError(List *rstates, Oid subid, char *slotname, char *err);
+static void CheckAlterSubOption(Subscription *sub, const char *option,
+								bool isTopLevel);
 
 
 /*
@@ -259,21 +262,9 @@ parse_subscription_options(ParseState *pstate, List *stmt_options,
 			opts->specified_opts |= SUBOPT_STREAMING;
 			opts->streaming = defGetStreamingMode(defel);
 		}
-		else if (strcmp(defel->defname, "two_phase") == 0)
+		else if (IsSet(supported_opts, SUBOPT_TWOPHASE_COMMIT) &&
+				 strcmp(defel->defname, "two_phase") == 0)
 		{
-			/*
-			 * Do not allow toggling of two_phase option. Doing so could cause
-			 * missing of transactions and lead to an inconsistent replica.
-			 * See comments atop worker.c
-			 *
-			 * Note: Unsupported twophase indicates that this call originated
-			 * from AlterSubscription.
-			 */
-			if (!IsSet(supported_opts, SUBOPT_TWOPHASE_COMMIT))
-				ereport(ERROR,
-						(errcode(ERRCODE_SYNTAX_ERROR),
-						 errmsg("unrecognized subscription parameter: \"%s\"", defel->defname)));
-
 			if (IsSet(opts->specified_opts, SUBOPT_TWOPHASE_COMMIT))
 				errorConflictingDefElem(defel, pstate);
 
@@ -1079,6 +1070,44 @@ AlterSubscription_refresh(Subscription *sub, bool copy_data,
 		table_close(rel, NoLock);
 }
 
+/*
+ * Common checks for altering failover and two_phase option
+ */
+static void
+CheckAlterSubOption(Subscription *sub, const char *option, bool isTopLevel)
+{
+	StringInfoData cmd;
+
+	if (!sub->slotname)
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("cannot set %s for a subscription that does not have a slot name",
+						option)));
+
+	/*
+	 * Do not allow changing the option if the subscription is enabled. This
+	 * is because both failover and two_phase options of the slot on the
+	 * publisher cannot be modified if the slot is currently acquired by the
+	 * apply worker.
+	 */
+	if (sub->enabled)
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("cannot set %s for enabled subscription",
+						option)));
+
+	initStringInfo(&cmd);
+	appendStringInfo(&cmd, "ALTER SUBSCRIPTION ... SET (%s)", option);
+
+	/*
+	 * The changed option of the slot can't be rolled back: prevent we are in
+	 * the transaction state.
+	 */
+	PreventInTransactionBlock(isTopLevel, cmd.data);
+
+	pfree(cmd.data);
+}
+
 /*
  * Alter the existing subscription.
  */
@@ -1145,7 +1174,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 			{
 				supported_opts = (SUBOPT_SLOT_NAME |
 								  SUBOPT_SYNCHRONOUS_COMMIT | SUBOPT_BINARY |
-								  SUBOPT_STREAMING | SUBOPT_DISABLE_ON_ERR |
+								  SUBOPT_STREAMING | SUBOPT_TWOPHASE_COMMIT |
+								  SUBOPT_DISABLE_ON_ERR |
 								  SUBOPT_PASSWORD_REQUIRED |
 								  SUBOPT_RUN_AS_OWNER | SUBOPT_FAILOVER |
 								  SUBOPT_ORIGIN);
@@ -1229,33 +1259,59 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 
 				if (IsSet(opts.specified_opts, SUBOPT_FAILOVER))
 				{
-					if (!sub->slotname)
+					CheckAlterSubOption(sub, "failover", isTopLevel);
+
+					values[Anum_pg_subscription_subfailover - 1] =
+						BoolGetDatum(opts.failover);
+					replaces[Anum_pg_subscription_subfailover - 1] = true;
+				}
+
+				if (IsSet(opts.specified_opts, SUBOPT_TWOPHASE_COMMIT))
+				{
+					CheckAlterSubOption(sub, "two_phase", isTopLevel);
+
+					/*
+					 * slot_name and two_phase cannot be altered
+					 * simultaneously. The latter part refers to the pre-set
+					 * slot name and tries to modify the slot option, so
+					 * changing both does not make sense.
+					 */
+					if (IsSet(opts.specified_opts, SUBOPT_SLOT_NAME))
 						ereport(ERROR,
-								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-								 errmsg("cannot set %s for a subscription that does not have a slot name",
-										"failover")));
+								(errcode(ERRCODE_SYNTAX_ERROR),
+								 errmsg("slot_name and two_phase cannot be altered at the same time")));
 
 					/*
-					 * Do not allow changing the failover state if the
-					 * subscription is enabled. This is because the failover
-					 * state of the slot on the publisher cannot be modified
-					 * if the slot is currently acquired by the apply worker.
+					 * Workers may still survive even if the subscription has
+					 * been disabled. They may read the pg_subscription
+					 * catalog and detect that the twophase parameter is
+					 * updated, which causes the assertion failure. Ensure
+					 * workers have already been exited to avoid it.
 					 */
-					if (sub->enabled)
+					if (logicalrep_workers_find(subid, true, true))
 						ereport(ERROR,
 								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-								 errmsg("cannot set %s for enabled subscription",
-										"failover")));
+								 errmsg("cannot alter two_phase when logical replication worker is still running"),
+								 errhint("Wait certain time and try again.")));
 
 					/*
-					 * The changed failover option of the slot can't be rolled
-					 * back.
+					 * two_phase cannot be disabled if there are any
+					 * uncommitted prepared transactions present.
 					 */
-					PreventInTransactionBlock(isTopLevel, "ALTER SUBSCRIPTION ... SET (failover)");
-
-					values[Anum_pg_subscription_subfailover - 1] =
-						BoolGetDatum(opts.failover);
-					replaces[Anum_pg_subscription_subfailover - 1] = true;
+					if (!opts.twophase &&
+						sub->twophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
+						LookupGXactBySubid(subid))
+						ereport(ERROR,
+								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+								 errmsg("cannot disable two_phase when prepared transactions are present"),
+								 errhint("Resolve these transactions and try again.")));
+
+					/* Change system catalog acoordingly */
+					values[Anum_pg_subscription_subtwophasestate - 1] =
+						CharGetDatum(opts.twophase ?
+									 LOGICALREP_TWOPHASE_STATE_PENDING :
+									 LOGICALREP_TWOPHASE_STATE_DISABLED);
+					replaces[Anum_pg_subscription_subtwophasestate - 1] = true;
 				}
 
 				if (IsSet(opts.specified_opts, SUBOPT_ORIGIN))
@@ -1507,7 +1563,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 	 * doing the database operations we won't be able to rollback altered
 	 * slot.
 	 */
-	if (replaces[Anum_pg_subscription_subfailover - 1])
+	if (replaces[Anum_pg_subscription_subfailover - 1] ||
+		replaces[Anum_pg_subscription_subtwophasestate - 1])
 	{
 		bool		must_use_password;
 		char	   *err;
@@ -1528,7 +1585,7 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 
 		PG_TRY();
 		{
-			walrcv_alter_slot(wrconn, sub->slotname, opts.failover);
+			walrcv_alter_slot(wrconn, sub->slotname, opts.failover, opts.twophase);
 		}
 		PG_FINALLY();
 		{
@@ -1675,9 +1732,7 @@ DropSubscription(DropSubscriptionStmt *stmt, bool isTopLevel)
 	 * New workers won't be started because we hold an exclusive lock on the
 	 * subscription till the end of the transaction.
 	 */
-	LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
-	subworkers = logicalrep_workers_find(subid, false);
-	LWLockRelease(LogicalRepWorkerLock);
+	subworkers = logicalrep_workers_find(subid, false, true);
 	foreach(lc, subworkers)
 	{
 		LogicalRepWorker *w = (LogicalRepWorker *) lfirst(lc);
diff --git a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
index 6c42c209d2..1cb601a148 100644
--- a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
+++ b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
@@ -80,7 +80,7 @@ static char *libpqrcv_create_slot(WalReceiverConn *conn,
 								  CRSSnapshotAction snapshot_action,
 								  XLogRecPtr *lsn);
 static void libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-								bool failover);
+								bool failover, bool two_phase);
 static pid_t libpqrcv_get_backend_pid(WalReceiverConn *conn);
 static WalRcvExecResult *libpqrcv_exec(WalReceiverConn *conn,
 									   const char *query,
@@ -1121,15 +1121,16 @@ libpqrcv_create_slot(WalReceiverConn *conn, const char *slotname,
  */
 static void
 libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-					bool failover)
+					bool failover, bool two_phase)
 {
 	StringInfoData cmd;
 	PGresult   *res;
 
 	initStringInfo(&cmd);
-	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( FAILOVER %s )",
+	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( FAILOVER %s, TWO_PHASE %s )",
 					 quote_identifier(slotname),
-					 failover ? "true" : "false");
+					 failover ? "true" : "false",
+					 two_phase ? "true" : "false");
 
 	res = libpqrcv_PQexec(conn->streamConn, cmd.data);
 	pfree(cmd.data);
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 27c3a91fb7..45744b771f 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -272,12 +272,15 @@ logicalrep_worker_find(Oid subid, Oid relid, bool only_running)
  * the subscription, instead of just one.
  */
 List *
-logicalrep_workers_find(Oid subid, bool only_running)
+logicalrep_workers_find(Oid subid, bool only_running, bool require_lock)
 {
 	int			i;
 	List	   *res = NIL;
 
-	Assert(LWLockHeldByMe(LogicalRepWorkerLock));
+	if (require_lock)
+		LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
+	else
+		Assert(LWLockHeldByMe(LogicalRepWorkerLock));
 
 	/* Search for attached worker for a given subscription id. */
 	for (i = 0; i < max_logical_replication_workers; i++)
@@ -288,6 +291,9 @@ logicalrep_workers_find(Oid subid, bool only_running)
 			res = lappend(res, w);
 	}
 
+	if (require_lock)
+		LWLockRelease(LogicalRepWorkerLock);
+
 	return res;
 }
 
@@ -759,7 +765,7 @@ logicalrep_worker_detach(void)
 
 		LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
 
-		workers = logicalrep_workers_find(MyLogicalRepWorker->subid, true);
+		workers = logicalrep_workers_find(MyLogicalRepWorker->subid, true, false);
 		foreach(lc, workers)
 		{
 			LogicalRepWorker *w = (LogicalRepWorker *) lfirst(lc);
diff --git a/src/backend/replication/logical/worker.c b/src/backend/replication/logical/worker.c
index c0bda6269b..6c798cd5b4 100644
--- a/src/backend/replication/logical/worker.c
+++ b/src/backend/replication/logical/worker.c
@@ -401,9 +401,6 @@ static void apply_handle_tuple_routing(ApplyExecutionData *edata,
 									   LogicalRepTupleData *newtup,
 									   CmdType operation);
 
-/* Compute GID for two_phase transactions */
-static void TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid, int szgid);
-
 /* Functions for skipping changes */
 static void maybe_start_skipping_changes(XLogRecPtr finish_lsn);
 static void stop_skipping_changes(void);
@@ -3911,7 +3908,7 @@ maybe_reread_subscription(void)
 	/* !slotname should never happen when enabled is true. */
 	Assert(newsub->slotname);
 
-	/* two-phase should not be altered */
+	/* two-phase cannot be altered while the worker exists */
 	Assert(newsub->twophasestate == MySubscription->twophasestate);
 
 	/*
@@ -4396,24 +4393,6 @@ cleanup_subxact_info()
 	subxact_data.nsubxacts_max = 0;
 }
 
-/*
- * Form the prepared transaction GID for two_phase transactions.
- *
- * Return the GID in the supplied buffer.
- */
-static void
-TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid, int szgid)
-{
-	Assert(subid != InvalidRepOriginId);
-
-	if (!TransactionIdIsValid(xid))
-		ereport(ERROR,
-				(errcode(ERRCODE_PROTOCOL_VIOLATION),
-				 errmsg_internal("invalid two-phase transaction ID")));
-
-	snprintf(gid, szgid, "pg_gid_%u_%u", subid, xid);
-}
-
 /*
  * Common function to run the apply loop with error handling. Disable the
  * subscription, if necessary.
@@ -5014,7 +4993,7 @@ AtEOXact_LogicalRepWorkers(bool isCommit)
 			List	   *workers;
 			ListCell   *lc2;
 
-			workers = logicalrep_workers_find(subid, true);
+			workers = logicalrep_workers_find(subid, true, false);
 			foreach(lc2, workers)
 			{
 				LogicalRepWorker *worker = (LogicalRepWorker *) lfirst(lc2);
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index baf9b89dc4..2f167a2adc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -804,9 +804,12 @@ ReplicationSlotDrop(const char *name, bool nowait)
  * Change the definition of the slot identified by the specified name.
  */
 void
-ReplicationSlotAlter(const char *name, bool failover)
+ReplicationSlotAlter(const char *name, bool *failover, bool *two_phase)
 {
+	bool		update_slot = false;
+
 	Assert(MyReplicationSlot == NULL);
+	Assert(failover || two_phase);
 
 	ReplicationSlotAcquire(name, false);
 
@@ -832,7 +835,7 @@ ReplicationSlotAlter(const char *name, bool failover)
 		 * Do not allow users to enable failover on the standby as we do not
 		 * support sync to the cascading standby.
 		 */
-		if (failover)
+		if (failover && *failover)
 			ereport(ERROR,
 					errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 					errmsg("cannot enable failover for a replication slot"
@@ -843,17 +846,32 @@ ReplicationSlotAlter(const char *name, bool failover)
 	 * Do not allow users to enable failover for temporary slots as we do not
 	 * support syncing temporary slots to the standby.
 	 */
-	if (failover && MyReplicationSlot->data.persistency == RS_TEMPORARY)
+	if (failover && *failover &&
+		MyReplicationSlot->data.persistency == RS_TEMPORARY)
 		ereport(ERROR,
 				errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 				errmsg("cannot enable failover for a temporary replication slot"));
 
-	if (MyReplicationSlot->data.failover != failover)
+	if (failover && MyReplicationSlot->data.failover != *failover)
+	{
+		SpinLockAcquire(&MyReplicationSlot->mutex);
+		MyReplicationSlot->data.failover = *failover;
+		SpinLockRelease(&MyReplicationSlot->mutex);
+
+		update_slot = true;
+	}
+
+	if (two_phase && MyReplicationSlot->data.two_phase != *two_phase)
 	{
 		SpinLockAcquire(&MyReplicationSlot->mutex);
-		MyReplicationSlot->data.failover = failover;
+		MyReplicationSlot->data.two_phase = *two_phase;
 		SpinLockRelease(&MyReplicationSlot->mutex);
 
+		update_slot = true;
+	}
+
+	if (update_slot)
+	{
 		ReplicationSlotMarkDirty();
 		ReplicationSlotSave();
 	}
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 2d1a9ec900..f3b5068d95 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1410,22 +1410,34 @@ DropReplicationSlot(DropReplicationSlotCmd *cmd)
  * Process extra options given to ALTER_REPLICATION_SLOT.
  */
 static void
-ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd, bool *failover)
+ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd,
+						  bool *failover_given, bool *failover,
+						  bool *two_phase_given, bool *two_phase)
 {
-	bool		failover_given = false;
+	*failover_given = false;
+	*two_phase_given = false;
 
 	/* Parse options */
 	foreach_ptr(DefElem, defel, cmd->options)
 	{
 		if (strcmp(defel->defname, "failover") == 0)
 		{
-			if (failover_given)
+			if (*failover_given)
 				ereport(ERROR,
 						(errcode(ERRCODE_SYNTAX_ERROR),
 						 errmsg("conflicting or redundant options")));
-			failover_given = true;
+			*failover_given = true;
 			*failover = defGetBoolean(defel);
 		}
+		else if (strcmp(defel->defname, "two_phase") == 0)
+		{
+			if (*two_phase_given)
+				ereport(ERROR,
+						(errcode(ERRCODE_SYNTAX_ERROR),
+						 errmsg("conflicting or redundant options")));
+			*two_phase_given = true;
+			*two_phase = defGetBoolean(defel);
+		}
 		else
 			elog(ERROR, "unrecognized option: %s", defel->defname);
 	}
@@ -1437,10 +1449,17 @@ ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd, bool *failover)
 static void
 AlterReplicationSlot(AlterReplicationSlotCmd *cmd)
 {
-	bool		failover = false;
+	bool		failover_given;
+	bool		two_phase_given;
+	bool		failover;
+	bool		two_phase;
+
+	ParseAlterReplSlotOptions(cmd, &failover_given, &failover,
+							  &two_phase_given, &two_phase);
 
-	ParseAlterReplSlotOptions(cmd, &failover);
-	ReplicationSlotAlter(cmd->slotname, failover);
+	ReplicationSlotAlter(cmd->slotname,
+						 failover_given ? &failover : NULL,
+						 two_phase_given ? &two_phase : NULL);
 }
 
 /*
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
index d453e224d9..891face1b6 100644
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -1948,7 +1948,7 @@ psql_completion(const char *text, int start, int end)
 	else if (HeadMatches("ALTER", "SUBSCRIPTION", MatchAny) && TailMatches("SET", "("))
 		COMPLETE_WITH("binary", "disable_on_error", "failover", "origin",
 					  "password_required", "run_as_owner", "slot_name",
-					  "streaming", "synchronous_commit");
+					  "streaming", "synchronous_commit", "two_phase");
 	/* ALTER SUBSCRIPTION <name> SKIP ( */
 	else if (HeadMatches("ALTER", "SUBSCRIPTION", MatchAny) && TailMatches("SKIP", "("))
 		COMPLETE_WITH("lsn");
diff --git a/src/include/access/twophase.h b/src/include/access/twophase.h
index 56248c0006..d37e06fdee 100644
--- a/src/include/access/twophase.h
+++ b/src/include/access/twophase.h
@@ -62,4 +62,9 @@ extern void PrepareRedoRemove(TransactionId xid, bool giveWarning);
 extern void restoreTwoPhaseData(void);
 extern bool LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 						TimestampTz origin_prepare_timestamp);
+
+extern void TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid,
+								   int szgid);
+extern bool LookupGXactBySubid(Oid subid);
+
 #endif							/* TWOPHASE_H */
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index c9675ee87c..cde164472a 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -243,7 +243,8 @@ extern void ReplicationSlotCreate(const char *name, bool db_specific,
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
 extern void ReplicationSlotDropAcquired(void);
-extern void ReplicationSlotAlter(const char *name, bool failover);
+extern void ReplicationSlotAlter(const char *name, bool *failover,
+								 bool *two_phase);
 
 extern void ReplicationSlotAcquire(const char *name, bool nowait);
 extern void ReplicationSlotRelease(void);
diff --git a/src/include/replication/walreceiver.h b/src/include/replication/walreceiver.h
index 12f71fa99b..31fa1257ec 100644
--- a/src/include/replication/walreceiver.h
+++ b/src/include/replication/walreceiver.h
@@ -372,12 +372,13 @@ typedef char *(*walrcv_create_slot_fn) (WalReceiverConn *conn,
 /*
  * walrcv_alter_slot_fn
  *
- * Change the definition of a replication slot. Currently, it only supports
- * changing the failover property of the slot.
+ * Change the definition of a replication slot. Currently, it supports
+ * changing the failover and the two_phase property of the slot.
  */
 typedef void (*walrcv_alter_slot_fn) (WalReceiverConn *conn,
 									  const char *slotname,
-									  bool failover);
+									  bool failover,
+									  bool two_phase);
 
 /*
  * walrcv_get_backend_pid_fn
@@ -455,8 +456,8 @@ extern PGDLLIMPORT WalReceiverFunctionsType *WalReceiverFunctions;
 	WalReceiverFunctions->walrcv_send(conn, buffer, nbytes)
 #define walrcv_create_slot(conn, slotname, temporary, two_phase, failover, snapshot_action, lsn) \
 	WalReceiverFunctions->walrcv_create_slot(conn, slotname, temporary, two_phase, failover, snapshot_action, lsn)
-#define walrcv_alter_slot(conn, slotname, failover) \
-	WalReceiverFunctions->walrcv_alter_slot(conn, slotname, failover)
+#define walrcv_alter_slot(conn, slotname, failover, two_phase) \
+	WalReceiverFunctions->walrcv_alter_slot(conn, slotname, failover, two_phase)
 #define walrcv_get_backend_pid(conn) \
 	WalReceiverFunctions->walrcv_get_backend_pid(conn)
 #define walrcv_exec(conn, exec, nRetTypes, retTypes) \
diff --git a/src/include/replication/worker_internal.h b/src/include/replication/worker_internal.h
index 515aefd519..990f5242f9 100644
--- a/src/include/replication/worker_internal.h
+++ b/src/include/replication/worker_internal.h
@@ -240,7 +240,8 @@ extern PGDLLIMPORT bool InitializingApplyWorker;
 extern void logicalrep_worker_attach(int slot);
 extern LogicalRepWorker *logicalrep_worker_find(Oid subid, Oid relid,
 												bool only_running);
-extern List *logicalrep_workers_find(Oid subid, bool only_running);
+extern List *logicalrep_workers_find(Oid subid, bool only_running,
+									 bool require_lock);
 extern bool logicalrep_worker_launch(LogicalRepWorkerType wtype,
 									 Oid dbid, Oid subid, const char *subname,
 									 Oid userid, Oid relid,
diff --git a/src/test/regress/expected/subscription.out b/src/test/regress/expected/subscription.out
index 5c2f1ee517..52ccb160fa 100644
--- a/src/test/regress/expected/subscription.out
+++ b/src/test/regress/expected/subscription.out
@@ -377,10 +377,7 @@ HINT:  To initiate replication, you must manually create the replication slot, e
  regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | p                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
---fail - alter of two_phase option not supported.
-ALTER SUBSCRIPTION regress_testsub SET (two_phase = false);
-ERROR:  unrecognized subscription parameter: "two_phase"
--- but can alter streaming when two_phase enabled
+-- We can alter streaming when two_phase enabled
 ALTER SUBSCRIPTION regress_testsub SET (streaming = true);
 \dRs+
                                                                                                                 List of subscriptions
diff --git a/src/test/regress/sql/subscription.sql b/src/test/regress/sql/subscription.sql
index 3e5ba4cb8c..a3886d79ca 100644
--- a/src/test/regress/sql/subscription.sql
+++ b/src/test/regress/sql/subscription.sql
@@ -256,10 +256,7 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUBLICATION testpub WITH (connect = false, two_phase = true);
 
 \dRs+
---fail - alter of two_phase option not supported.
-ALTER SUBSCRIPTION regress_testsub SET (two_phase = false);
-
--- but can alter streaming when two_phase enabled
+-- We can alter streaming when two_phase enabled
 ALTER SUBSCRIPTION regress_testsub SET (streaming = true);
 
 \dRs+
diff --git a/src/test/subscription/t/021_twophase.pl b/src/test/subscription/t/021_twophase.pl
index 9437cd4c3b..4e8f627f7b 100644
--- a/src/test/subscription/t/021_twophase.pl
+++ b/src/test/subscription/t/021_twophase.pl
@@ -367,6 +367,81 @@ $result =
   $node_subscriber->safe_psql('postgres', "SELECT count(*) FROM tab_copy;");
 is($result, qq(2), 'replicated data in subscriber table');
 
+# Clean up
+$node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub");
+
+###############################
+# Disable the subscription and alter it to two_phase = false,
+# then verify that the altered subscription reflects the two_phase option.
+###############################
+
+# Alter subscription two_phase to false
+$node_subscriber->safe_psql('postgres',
+    "ALTER SUBSCRIPTION tap_sub_copy DISABLE;");
+$node_subscriber->poll_query_until('postgres',
+    "SELECT count(*) = 0 FROM pg_stat_activity WHERE backend_type = 'logical replication worker'"
+);
+$node_subscriber->safe_psql(
+	'postgres', "
+    ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = false);
+    ALTER SUBSCRIPTION tap_sub_copy ENABLE;");
+
+# Wait for subscription startup
+$node_subscriber->wait_for_subscription_sync($node_publisher, $appname_copy);
+
+# Make sure that the two-phase is disabled on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT subtwophasestate FROM pg_subscription WHERE subname = 'tap_sub_copy';"
+);
+is($result, qq(d), 'two-phase should be disabled');
+
+# Now do a prepare on the publisher and make sure that it is not replicated.
+$node_publisher->safe_psql(
+	'postgres', qq{
+    BEGIN;
+    INSERT INTO tab_copy VALUES (100);
+    PREPARE TRANSACTION 'newgid';
+	});
+
+# Wait for the subscriber to catchup
+$node_publisher->wait_for_catchup($appname_copy);
+
+# Make sure there are no prepared transactions on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT count(*) FROM pg_prepared_xacts;");
+is($result, qq(0), 'should be no prepared transactions on subscriber');
+
+# Now commit the insert and verify that it is replicated
+$node_publisher->safe_psql('postgres', "COMMIT PREPARED 'newgid';");
+
+# Wait for the subscriber to catchup
+$node_publisher->wait_for_catchup($appname_copy);
+
+# Make sure that the committed transaction is replicated.
+$result =
+  $node_subscriber->safe_psql('postgres', "SELECT count(*) FROM tab_copy;");
+is($result, qq(3), 'replicated data in subscriber table');
+
+# Alter subscription two_phase to true
+$node_subscriber->safe_psql('postgres',
+    "ALTER SUBSCRIPTION tap_sub_copy DISABLE;");
+$node_subscriber->poll_query_until('postgres',
+    "SELECT count(*) = 0 FROM pg_stat_activity WHERE backend_type = 'logical replication worker'"
+);
+$node_subscriber->safe_psql(
+	'postgres', "
+    ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = true);
+    ALTER SUBSCRIPTION tap_sub_copy ENABLE;");
+
+# Wait for subscription startup
+$node_subscriber->wait_for_subscription_sync($node_publisher, $appname_copy);
+
+# Make sure that the two-phase is enabled on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT subtwophasestate FROM pg_subscription WHERE subname = 'tap_sub_copy';"
+);
+is($result, qq(e), 'two-phase should be enabled');
+
 $node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub_copy;");
 $node_publisher->safe_psql('postgres', "DROP PUBLICATION tap_pub_copy;");
 
@@ -374,8 +449,6 @@ $node_publisher->safe_psql('postgres', "DROP PUBLICATION tap_pub_copy;");
 # check all the cleanup
 ###############################
 
-$node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub");
-
 $result = $node_subscriber->safe_psql('postgres',
 	"SELECT count(*) FROM pg_subscription");
 is($result, qq(0), 'check subscription was dropped on subscriber');
-- 
2.43.0

From e63c14572a34efa4639e038a3c50e930f710d06c Mon Sep 17 00:00:00 2001
From: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Date: Wed, 17 Apr 2024 06:18:23 +0000
Subject: [PATCH v18 2/3] Alter slot option two_phase only when altering "true"
 to "false"

Since the two_phase option is controlled by both the publisher (as a slot option)
and the subscriber (as a subscription option), the slot option must also be
modified.

Regarding the false->true case, the backend process alters the subtwophase to
LOGICALREP_TWOPHASE_STATE_PENDING once. After the subscription is enabled, a new
logical replication worker requests to change the two_phase option of its slot
from pending to true after the initial data synchronization is done. The code
path is the same as the case in which two_phase is initially set to true, so
there is no need to do something remarkable. However, for the true->false case,
the backend must connect to the publisher and expressly change the parameter
because the apply worker does not alter the option to false. Because this
operation cannot be rolled back, altering the two_phase parameter from "true"
to "false" within a transaction is prohibited.
---
 doc/src/sgml/ref/alter_subscription.sgml      |  2 +-
 src/backend/commands/subscriptioncmds.c       | 80 ++++++++++++++-----
 .../libpqwalreceiver/libpqwalreceiver.c       | 23 ++++--
 src/include/replication/walreceiver.h         |  5 +-
 src/test/subscription/t/021_twophase.pl       | 41 ++++++----
 5 files changed, 105 insertions(+), 46 deletions(-)

diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index 0b23df1b77..df44415661 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -70,7 +70,7 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
    <command>ALTER SUBSCRIPTION ... {SET|ADD|DROP} PUBLICATION ...</command>
    with <literal>refresh</literal> option as <literal>true</literal>,
    <command>ALTER SUBSCRIPTION ... SET (failover = true|false)</command> and
-   <command>ALTER SUBSCRIPTION ... SET (two_phase = true|false)</command>
+   <command>ALTER SUBSCRIPTION ... SET (two_phase = false)</command>
    cannot be executed inside a transaction block.
 
    These commands also cannot be executed when the subscription has
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index d7e2b141b3..f09a6bb290 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -111,7 +111,7 @@ static void check_duplicates_in_publist(List *publist, Datum *datums);
 static List *merge_publications(List *oldpublist, List *newpublist, bool addpub, const char *subname);
 static void ReportSlotConnectionError(List *rstates, Oid subid, char *slotname, char *err);
 static void CheckAlterSubOption(Subscription *sub, const char *option,
-								bool isTopLevel);
+								bool needs_update, bool isTopLevel);
 
 
 /*
@@ -1074,11 +1074,9 @@ AlterSubscription_refresh(Subscription *sub, bool copy_data,
  * Common checks for altering failover and two_phase option
  */
 static void
-CheckAlterSubOption(Subscription *sub, const char *option, bool isTopLevel)
+CheckAlterSubOption(Subscription *sub, const char *option, bool needs_update, bool isTopLevel)
 {
-	StringInfoData cmd;
-
-	if (!sub->slotname)
+	if (needs_update && !sub->slotname)
 		ereport(ERROR,
 				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
 				 errmsg("cannot set %s for a subscription that does not have a slot name",
@@ -1096,16 +1094,20 @@ CheckAlterSubOption(Subscription *sub, const char *option, bool isTopLevel)
 				 errmsg("cannot set %s for enabled subscription",
 						option)));
 
-	initStringInfo(&cmd);
-	appendStringInfo(&cmd, "ALTER SUBSCRIPTION ... SET (%s)", option);
-
 	/*
 	 * The changed option of the slot can't be rolled back: prevent we are in
 	 * the transaction state.
 	 */
-	PreventInTransactionBlock(isTopLevel, cmd.data);
+	if (needs_update)
+	{
+		StringInfoData cmd;
 
-	pfree(cmd.data);
+		initStringInfo(&cmd);
+		appendStringInfo(&cmd, "ALTER SUBSCRIPTION ... SET (%s)", option);
+
+		PreventInTransactionBlock(isTopLevel, cmd.data);
+		pfree(cmd.data);
+	}
 }
 
 /*
@@ -1127,6 +1129,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 	Form_pg_subscription form;
 	bits32		supported_opts;
 	SubOpts		opts = {0};
+	bool		update_failover = false;
+	bool		update_two_phase = false;
 
 	rel = table_open(SubscriptionRelationId, RowExclusiveLock);
 
@@ -1259,7 +1263,16 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 
 				if (IsSet(opts.specified_opts, SUBOPT_FAILOVER))
 				{
-					CheckAlterSubOption(sub, "failover", isTopLevel);
+					/*
+					 * First mark the needs to alter the replication slot.
+					 * Failover option is controlled by both the publisher (as
+					 * a slot option) and the subscriber (as a subscription
+					 * option).
+					 */
+					update_failover = true;
+
+					CheckAlterSubOption(sub, "failover", update_failover,
+										isTopLevel);
 
 					values[Anum_pg_subscription_subfailover - 1] =
 						BoolGetDatum(opts.failover);
@@ -1268,15 +1281,37 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 
 				if (IsSet(opts.specified_opts, SUBOPT_TWOPHASE_COMMIT))
 				{
-					CheckAlterSubOption(sub, "two_phase", isTopLevel);
+					/*
+					 * First check the need to alter the replication slot.
+					 * Two_phase option is controlled by both the publisher
+					 * (as a slot option) and the subscriber (as a
+					 * subscription option). The slot option must be altered
+					 * only when changing "true" to "false".
+					 *
+					 * There is no need to do something remarkable regarding
+					 * the "false" to "true" case; the backend process alters
+					 * subtwophase to LOGICALREP_TWOPHASE_STATE_PENDING once.
+					 * After the subscription is enabled, a new logical
+					 * replication worker requests to change the two_phase
+					 * option of its slot from pending to true when the
+					 * initial data synchronization is done. The code path is
+					 * the same as the case in which two_phase is initially
+					 * set to true.
+					 */
+					update_two_phase = !opts.twophase;
+
+					CheckAlterSubOption(sub, "two_phase", update_two_phase,
+										isTopLevel);
 
 					/*
-					 * slot_name and two_phase cannot be altered
-					 * simultaneously. The latter part refers to the pre-set
-					 * slot name and tries to modify the slot option, so
-					 * changing both does not make sense.
+					 * If the wo_phase slot option must be altered, this
+					 * cannot be altered with slot_name simultaneously. The
+					 * latter part refers to the pre-set slot name and tries
+					 * to modify the slot option, so changing both does not
+					 * make sense.
 					 */
-					if (IsSet(opts.specified_opts, SUBOPT_SLOT_NAME))
+					if (update_two_phase &&
+						IsSet(opts.specified_opts, SUBOPT_SLOT_NAME))
 						ereport(ERROR,
 								(errcode(ERRCODE_SYNTAX_ERROR),
 								 errmsg("slot_name and two_phase cannot be altered at the same time")));
@@ -1298,7 +1333,7 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 					 * two_phase cannot be disabled if there are any
 					 * uncommitted prepared transactions present.
 					 */
-					if (!opts.twophase &&
+					if (update_two_phase &&
 						sub->twophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
 						LookupGXactBySubid(subid))
 						ereport(ERROR,
@@ -1557,14 +1592,13 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 	}
 
 	/*
-	 * Try to acquire the connection necessary for altering slot.
+	 * Try to acquire the connection necessary for altering slot, if needed.
 	 *
 	 * This has to be at the end because otherwise if there is an error while
 	 * doing the database operations we won't be able to rollback altered
 	 * slot.
 	 */
-	if (replaces[Anum_pg_subscription_subfailover - 1] ||
-		replaces[Anum_pg_subscription_subtwophasestate - 1])
+	if (update_failover || update_two_phase)
 	{
 		bool		must_use_password;
 		char	   *err;
@@ -1585,7 +1619,9 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 
 		PG_TRY();
 		{
-			walrcv_alter_slot(wrconn, sub->slotname, opts.failover, opts.twophase);
+			walrcv_alter_slot(wrconn, sub->slotname,
+							  update_failover ? &opts.failover : NULL,
+							  update_two_phase ? &opts.twophase : NULL);
 		}
 		PG_FINALLY();
 		{
diff --git a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
index 1cb601a148..97f957cd87 100644
--- a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
+++ b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
@@ -80,7 +80,7 @@ static char *libpqrcv_create_slot(WalReceiverConn *conn,
 								  CRSSnapshotAction snapshot_action,
 								  XLogRecPtr *lsn);
 static void libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-								bool failover, bool two_phase);
+								const bool *failover, const bool *two_phase);
 static pid_t libpqrcv_get_backend_pid(WalReceiverConn *conn);
 static WalRcvExecResult *libpqrcv_exec(WalReceiverConn *conn,
 									   const char *query,
@@ -1121,16 +1121,27 @@ libpqrcv_create_slot(WalReceiverConn *conn, const char *slotname,
  */
 static void
 libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-					bool failover, bool two_phase)
+					const bool *failover, const bool *two_phase)
 {
 	StringInfoData cmd;
 	PGresult   *res;
 
 	initStringInfo(&cmd);
-	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( FAILOVER %s, TWO_PHASE %s )",
-					 quote_identifier(slotname),
-					 failover ? "true" : "false",
-					 two_phase ? "true" : "false");
+	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( ",
+					 quote_identifier(slotname));
+
+	if (failover)
+		appendStringInfo(&cmd, "FAILOVER %s",
+						 *failover ? "true" : "false");
+
+	if (failover && two_phase)
+		appendStringInfo(&cmd, ", ");
+
+	if (two_phase)
+		appendStringInfo(&cmd, "TWO_PHASE %s",
+						 *two_phase ? "true" : "false");
+
+	appendStringInfoString(&cmd, " );");
 
 	res = libpqrcv_PQexec(conn->streamConn, cmd.data);
 	pfree(cmd.data);
diff --git a/src/include/replication/walreceiver.h b/src/include/replication/walreceiver.h
index 31fa1257ec..7ffa5a58b3 100644
--- a/src/include/replication/walreceiver.h
+++ b/src/include/replication/walreceiver.h
@@ -377,8 +377,9 @@ typedef char *(*walrcv_create_slot_fn) (WalReceiverConn *conn,
  */
 typedef void (*walrcv_alter_slot_fn) (WalReceiverConn *conn,
 									  const char *slotname,
-									  bool failover,
-									  bool two_phase);
+									  const bool *failover,
+									  const bool *two_phase);
+
 
 /*
  * walrcv_get_backend_pid_fn
diff --git a/src/test/subscription/t/021_twophase.pl b/src/test/subscription/t/021_twophase.pl
index 4e8f627f7b..f56dff4b12 100644
--- a/src/test/subscription/t/021_twophase.pl
+++ b/src/test/subscription/t/021_twophase.pl
@@ -375,6 +375,12 @@ $node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub");
 # then verify that the altered subscription reflects the two_phase option.
 ###############################
 
+# Confirm two-phase slot option is enabled before altering
+$result = $node_publisher->safe_psql('postgres',
+	"SELECT two_phase FROM pg_replication_slots WHERE slot_name = 'tap_sub_copy';"
+);
+is($result, qq(t), 'two-phase is enabled');
+
 # Alter subscription two_phase to false
 $node_subscriber->safe_psql('postgres',
     "ALTER SUBSCRIPTION tap_sub_copy DISABLE;");
@@ -393,7 +399,13 @@ $node_subscriber->wait_for_subscription_sync($node_publisher, $appname_copy);
 $result = $node_subscriber->safe_psql('postgres',
 	"SELECT subtwophasestate FROM pg_subscription WHERE subname = 'tap_sub_copy';"
 );
-is($result, qq(d), 'two-phase should be disabled');
+is($result, qq(d), 'two-phase subscription option should be disabled');
+
+# Make sure that the two-phase slot option is also disabled
+$result = $node_publisher->safe_psql('postgres',
+	"SELECT two_phase FROM pg_replication_slots WHERE slot_name = 'tap_sub_copy';"
+);
+is($result, qq(f), 'two-phase slot option should be disabled');
 
 # Now do a prepare on the publisher and make sure that it is not replicated.
 $node_publisher->safe_psql(
@@ -411,6 +423,19 @@ $result = $node_subscriber->safe_psql('postgres',
 	"SELECT count(*) FROM pg_prepared_xacts;");
 is($result, qq(0), 'should be no prepared transactions on subscriber');
 
+# Toggle the two_phase to "true" *before* the COMMIT PREPARED. Since we are the
+# special path for the case where both two_phase and failover are altered, it
+# is also set to "true".
+$node_subscriber->safe_psql('postgres',
+    "ALTER SUBSCRIPTION tap_sub_copy DISABLE;");
+$node_subscriber->poll_query_until('postgres',
+    "SELECT count(*) = 0 FROM pg_stat_activity WHERE backend_type = 'logical replication worker'"
+);
+$node_subscriber->safe_psql(
+	'postgres', "
+    ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = true, failover = true);
+    ALTER SUBSCRIPTION tap_sub_copy ENABLE;");
+
 # Now commit the insert and verify that it is replicated
 $node_publisher->safe_psql('postgres', "COMMIT PREPARED 'newgid';");
 
@@ -422,20 +447,6 @@ $result =
   $node_subscriber->safe_psql('postgres', "SELECT count(*) FROM tab_copy;");
 is($result, qq(3), 'replicated data in subscriber table');
 
-# Alter subscription two_phase to true
-$node_subscriber->safe_psql('postgres',
-    "ALTER SUBSCRIPTION tap_sub_copy DISABLE;");
-$node_subscriber->poll_query_until('postgres',
-    "SELECT count(*) = 0 FROM pg_stat_activity WHERE backend_type = 'logical replication worker'"
-);
-$node_subscriber->safe_psql(
-	'postgres', "
-    ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = true);
-    ALTER SUBSCRIPTION tap_sub_copy ENABLE;");
-
-# Wait for subscription startup
-$node_subscriber->wait_for_subscription_sync($node_publisher, $appname_copy);
-
 # Make sure that the two-phase is enabled on the subscriber
 $result = $node_subscriber->safe_psql('postgres',
 	"SELECT subtwophasestate FROM pg_subscription WHERE subname = 'tap_sub_copy';"
-- 
2.43.0

From 17eba2b13eb220f4885e4dcdadefc4edd6409844 Mon Sep 17 00:00:00 2001
From: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Date: Tue, 9 Jul 2024 08:01:43 +0000
Subject: [PATCH v18 3/3] Notify users to roll back prepared transactions

---
 doc/src/sgml/ref/alter_subscription.sgml | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index df44415661..e021f8729b 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -233,8 +233,6 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>, and
       <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>.
       Only a superuser can set <literal>password_required = false</literal>.
-      The <literal>two_phase</literal> parameter can only be altered when the
-      subscription is disabled.
      </para>
 
      <para>
@@ -256,6 +254,19 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>
       option is enabled.
      </para>
+
+     <para>
+      The <literal>two_phase</literal> parameter can only be altered when the
+      subscription is disabled. When altering the parameter from <literal>true</literal>
+      to <literal>false</literal>, the backend process checks for any incomplete
+      prepared transactions done by the logical replication worker (from when
+      <literal>two_phase</literal> parameter was still <literal>true</literal>)
+      and, if any are found, this command is failed with an error. In this
+      case, you can resolve prepared transactions on the publisher node or
+      manually roll back them on the subscriber. After the altering from
+      <literal>true</literal> to <literal>false</literal>, the publisher will
+      replicate transactions again when they are committed.
+     </para>
     </listitem>
    </varlistentry>
 
-- 
2.43.0

diff --git a/doc/src/sgml/protocol.sgml b/doc/src/sgml/protocol.sgml
index 3ac4a4b..cba6661 100644
--- a/doc/src/sgml/protocol.sgml
+++ b/doc/src/sgml/protocol.sgml
@@ -2050,21 +2050,6 @@ psql "dbname=postgres replication=database" -c "IDENTIFY_SYSTEM;"
 
       <variablelist>
        <varlistentry>
-        <term><literal>TWO_PHASE [ <replaceable class="parameter">boolean</replaceable> ]</literal></term>
-        <listitem>
-         <para>
-          If true, this logical replication slot supports decoding of two-phase
-          commit. With this option, commands related to two-phase commit such as
-          <literal>PREPARE TRANSACTION</literal>, <literal>COMMIT PREPARED</literal>
-          and <literal>ROLLBACK PREPARED</literal> are decoded and transmitted.
-          The transaction will be decoded and transmitted at
-          <literal>PREPARE TRANSACTION</literal> time.
-          The default is false.
-         </para>
-        </listitem>
-       </varlistentry>
-
-       <varlistentry>
         <term><literal>RESERVE_WAL [ <replaceable class="parameter">boolean</replaceable> ]</literal></term>
         <listitem>
          <para>
@@ -2104,6 +2089,21 @@ psql "dbname=postgres replication=database" -c "IDENTIFY_SYSTEM;"
          </para>
         </listitem>
        </varlistentry>
+
+       <varlistentry>
+        <term><literal>TWO_PHASE [ <replaceable class="parameter">boolean</replaceable> ]</literal></term>
+        <listitem>
+         <para>
+          If true, this logical replication slot supports decoding of two-phase
+          commit. With this option, commands related to two-phase commit such as
+          <literal>PREPARE TRANSACTION</literal>, <literal>COMMIT PREPARED</literal>
+          and <literal>ROLLBACK PREPARED</literal> are decoded and transmitted.
+          The transaction will be decoded and transmitted at
+          <literal>PREPARE TRANSACTION</literal> time.
+          The default is false.
+         </para>
+        </listitem>
+       </varlistentry>
       </variablelist>
 
       <para>
diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index 35bce68..f3c6e1f 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -2741,5 +2741,6 @@ LookupGXactBySubid(Oid subid)
 		}
 	}
 	LWLockRelease(TwoPhaseStateLock);
+
 	return found;
 }
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index 6995a62..3703cf6 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -1076,6 +1076,8 @@ CheckAlterSubOption(Subscription *sub, const char *option, bool isTopLevel)
 {
 	StringInfoData cmd;
 
+	Assert(strstr("two_phase,failover", option));
+
 	if (!sub->slotname)
 		ereport(ERROR,
 				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
@@ -1098,8 +1100,8 @@ CheckAlterSubOption(Subscription *sub, const char *option, bool isTopLevel)
 	appendStringInfo(&cmd, "ALTER SUBSCRIPTION ... SET (%s)", option);
 
 	/*
-	 * The changed option of the slot can't be rolled back: prevent we are in
-	 * the transaction state.
+	 * The changed option of the slot can't be rolled back, so disallow if we
+	 * are in a transaction block.
 	 */
 	PreventInTransactionBlock(isTopLevel, cmd.data);
 
@@ -1282,7 +1284,7 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 					/*
 					 * Workers may still survive even if the subscription has
 					 * been disabled. They may read the pg_subscription
-					 * catalog and detect that the twophase parameter is
+					 * catalog and detect that the two_phase parameter is
 					 * updated, which causes the assertion failure. Ensure
 					 * workers have already been exited to avoid it.
 					 */
@@ -1304,7 +1306,7 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 								 errmsg("cannot disable two_phase when prepared transactions are present"),
 								 errhint("Resolve these transactions and try again.")));
 
-					/* Change system catalog acoordingly */
+					/* Change system catalog accordingly */
 					values[Anum_pg_subscription_subtwophasestate - 1] =
 						CharGetDatum(opts.twophase ?
 									 LOGICALREP_TWOPHASE_STATE_PENDING :
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 45744b7..c566d50 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -272,15 +272,15 @@ logicalrep_worker_find(Oid subid, Oid relid, bool only_running)
  * the subscription, instead of just one.
  */
 List *
-logicalrep_workers_find(Oid subid, bool only_running, bool require_lock)
+logicalrep_workers_find(Oid subid, bool only_running, bool acquire_lock)
 {
 	int			i;
 	List	   *res = NIL;
 
-	if (require_lock)
+	if (acquire_lock)
 		LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
-	else
-		Assert(LWLockHeldByMe(LogicalRepWorkerLock));
+
+	Assert(LWLockHeldByMe(LogicalRepWorkerLock));
 
 	/* Search for attached worker for a given subscription id. */
 	for (i = 0; i < max_logical_replication_workers; i++)
@@ -291,7 +291,7 @@ logicalrep_workers_find(Oid subid, bool only_running, bool require_lock)
 			res = lappend(res, w);
 	}
 
-	if (require_lock)
+	if (acquire_lock)
 		LWLockRelease(LogicalRepWorkerLock);
 
 	return res;
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 2f167a2..e75f24b 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -842,23 +842,25 @@ ReplicationSlotAlter(const char *name, bool *failover, bool *two_phase)
 						   " on the standby"));
 	}
 
-	/*
-	 * Do not allow users to enable failover for temporary slots as we do not
-	 * support syncing temporary slots to the standby.
-	 */
-	if (failover && *failover &&
-		MyReplicationSlot->data.persistency == RS_TEMPORARY)
+	if (failover)
+	{
+		/*
+		 * Do not allow users to enable failover for temporary slots as we do not
+		 * support syncing temporary slots to the standby.
+		 */
+		if (*failover && MyReplicationSlot->data.persistency == RS_TEMPORARY)
 		ereport(ERROR,
 				errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 				errmsg("cannot enable failover for a temporary replication slot"));
 
-	if (failover && MyReplicationSlot->data.failover != *failover)
-	{
-		SpinLockAcquire(&MyReplicationSlot->mutex);
-		MyReplicationSlot->data.failover = *failover;
-		SpinLockRelease(&MyReplicationSlot->mutex);
+		if (MyReplicationSlot->data.failover != *failover)
+		{
+			SpinLockAcquire(&MyReplicationSlot->mutex);
+			MyReplicationSlot->data.failover = *failover;
+			SpinLockRelease(&MyReplicationSlot->mutex);
 
-		update_slot = true;
+			update_slot = true;
+		}
 	}
 
 	if (two_phase && MyReplicationSlot->data.two_phase != *two_phase)
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 04f65e0..af8e958 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1405,56 +1405,42 @@ DropReplicationSlot(DropReplicationSlotCmd *cmd)
 	ReplicationSlotDrop(cmd->slotname, !cmd->wait);
 }
 
+
 /*
- * Process extra options given to ALTER_REPLICATION_SLOT.
+ * Change the definition of a replication slot.
  */
 static void
-ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd,
-						  bool *failover_given, bool *failover,
-						  bool *two_phase_given, bool *two_phase)
+AlterReplicationSlot(AlterReplicationSlotCmd *cmd)
 {
-	*failover_given = false;
-	*two_phase_given = false;
+	bool		failover_given = false;
+	bool		two_phase_given = false;
+	bool		failover;
+	bool		two_phase;
 
 	/* Parse options */
 	foreach_ptr(DefElem, defel, cmd->options)
 	{
 		if (strcmp(defel->defname, "failover") == 0)
 		{
-			if (*failover_given)
+			if (failover_given)
 				ereport(ERROR,
 						(errcode(ERRCODE_SYNTAX_ERROR),
 						 errmsg("conflicting or redundant options")));
-			*failover_given = true;
-			*failover = defGetBoolean(defel);
+			failover_given = true;
+			failover = defGetBoolean(defel);
 		}
 		else if (strcmp(defel->defname, "two_phase") == 0)
 		{
-			if (*two_phase_given)
+			if (two_phase_given)
 				ereport(ERROR,
 						(errcode(ERRCODE_SYNTAX_ERROR),
 						 errmsg("conflicting or redundant options")));
-			*two_phase_given = true;
-			*two_phase = defGetBoolean(defel);
+			two_phase_given = true;
+			two_phase = defGetBoolean(defel);
 		}
 		else
 			elog(ERROR, "unrecognized option: %s", defel->defname);
 	}
-}
-
-/*
- * Change the definition of a replication slot.
- */
-static void
-AlterReplicationSlot(AlterReplicationSlotCmd *cmd)
-{
-	bool		failover_given;
-	bool		two_phase_given;
-	bool		failover;
-	bool		two_phase;
-
-	ParseAlterReplSlotOptions(cmd, &failover_given, &failover,
-							  &two_phase_given, &two_phase);
 
 	ReplicationSlotAlter(cmd->slotname,
 						 failover_given ? &failover : NULL,
diff --git a/src/include/replication/worker_internal.h b/src/include/replication/worker_internal.h
index 990f524..9646261 100644
--- a/src/include/replication/worker_internal.h
+++ b/src/include/replication/worker_internal.h
@@ -241,7 +241,7 @@ extern void logicalrep_worker_attach(int slot);
 extern LogicalRepWorker *logicalrep_worker_find(Oid subid, Oid relid,
 												bool only_running);
 extern List *logicalrep_workers_find(Oid subid, bool only_running,
-									 bool require_lock);
+									 bool acquire_lock);
 extern bool logicalrep_worker_launch(LogicalRepWorkerType wtype,
 									 Oid dbid, Oid subid, const char *subname,
 									 Oid userid, Oid relid,
diff --git a/src/test/regress/expected/subscription.out b/src/test/regress/expected/subscription.out
index 51fa4b9..40e1a07 100644
--- a/src/test/regress/expected/subscription.out
+++ b/src/test/regress/expected/subscription.out
@@ -377,7 +377,7 @@ HINT:  To initiate replication, you must manually create the replication slot, e
  regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | p                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
--- We can alter streaming when two_phase enabled
+-- we can alter streaming when two_phase is enabled
 ALTER SUBSCRIPTION regress_testsub SET (streaming = true);
 \dRs+
                                                                                                                 List of subscriptions
diff --git a/src/test/regress/sql/subscription.sql b/src/test/regress/sql/subscription.sql
index a3886d7..b64f419 100644
--- a/src/test/regress/sql/subscription.sql
+++ b/src/test/regress/sql/subscription.sql
@@ -256,7 +256,7 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUBLICATION testpub WITH (connect = false, two_phase = true);
 
 \dRs+
--- We can alter streaming when two_phase enabled
+-- we can alter streaming when two_phase is enabled
 ALTER SUBSCRIPTION regress_testsub SET (streaming = true);
 
 \dRs+
diff --git a/src/test/subscription/t/021_twophase.pl b/src/test/subscription/t/021_twophase.pl
index 4e8f627..66265c7 100644
--- a/src/test/subscription/t/021_twophase.pl
+++ b/src/test/subscription/t/021_twophase.pl
@@ -371,8 +371,8 @@ is($result, qq(2), 'replicated data in subscriber table');
 $node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub");
 
 ###############################
-# Disable the subscription and alter it to two_phase = false,
-# then verify that the altered subscription reflects the two_phase option.
+# Alter the subscription to two_phase = false.
+# Verify that the altered subscription reflects the two_phase option.
 ###############################
 
 # Alter subscription two_phase to false
@@ -395,7 +395,10 @@ $result = $node_subscriber->safe_psql('postgres',
 );
 is($result, qq(d), 'two-phase should be disabled');
 
-# Now do a prepare on the publisher and make sure that it is not replicated.
+###############################
+# Now do a prepare on the publisher.
+# Verify that it is not replicated.
+###############################
 $node_publisher->safe_psql(
 	'postgres', qq{
     BEGIN;
@@ -411,7 +414,10 @@ $result = $node_subscriber->safe_psql('postgres',
 	"SELECT count(*) FROM pg_prepared_xacts;");
 is($result, qq(0), 'should be no prepared transactions on subscriber');
 
-# Now commit the insert and verify that it is replicated
+###############################
+# Now commit the insert.
+# Verify that it is replicated.
+###############################
 $node_publisher->safe_psql('postgres', "COMMIT PREPARED 'newgid';");
 
 # Wait for the subscriber to catchup
@@ -422,7 +428,10 @@ $result =
   $node_subscriber->safe_psql('postgres', "SELECT count(*) FROM tab_copy;");
 is($result, qq(3), 'replicated data in subscriber table');
 
-# Alter subscription two_phase to true
+###############################
+# Alter the subscription to two_phase = true.
+# Verify that the altered subscription reflects the two_phase option.
+###############################
 $node_subscriber->safe_psql('postgres',
     "ALTER SUBSCRIPTION tap_sub_copy DISABLE;");
 $node_subscriber->poll_query_until('postgres',

diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index d80d60c..5c6f0a5 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -1262,7 +1262,7 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 				if (IsSet(opts.specified_opts, SUBOPT_FAILOVER))
 				{
 					/*
-					 * First mark the needs to alter the replication slot.
+					 * First, mark the need to alter the replication slot.
 					 * Failover option is controlled by both the publisher (as
 					 * a slot option) and the subscriber (as a subscription
 					 * option).
@@ -1280,7 +1280,7 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 				if (IsSet(opts.specified_opts, SUBOPT_TWOPHASE_COMMIT))
 				{
 					/*
-					 * First check the need to alter the replication slot.
+					 * First, check the need to alter the replication slot.
 					 * Two_phase option is controlled by both the publisher
 					 * (as a slot option) and the subscriber (as a
 					 * subscription option). The slot option must be altered
@@ -1302,11 +1302,9 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 										isTopLevel);
 
 					/*
-					 * If the wo_phase slot option must be altered, this
-					 * cannot be altered with slot_name simultaneously. The
-					 * latter part refers to the pre-set slot name and tries
-					 * to modify the slot option, so changing both does not
-					 * make sense.
+					 * Modifying the two_phase slot option requires a slot
+					 * lookup by slot name, so changing the slot name
+					 * at the same time is not allowed.
 					 */
 					if (update_two_phase &&
 						IsSet(opts.specified_opts, SUBOPT_SLOT_NAME))
diff --git a/src/test/subscription/t/021_twophase.pl b/src/test/subscription/t/021_twophase.pl
index f56dff4..26b9e2c 100644
--- a/src/test/subscription/t/021_twophase.pl
+++ b/src/test/subscription/t/021_twophase.pl
@@ -423,9 +423,12 @@ $result = $node_subscriber->safe_psql('postgres',
 	"SELECT count(*) FROM pg_prepared_xacts;");
 is($result, qq(0), 'should be no prepared transactions on subscriber');
 
-# Toggle the two_phase to "true" *before* the COMMIT PREPARED. Since we are the
-# special path for the case where both two_phase and failover are altered, it
-# is also set to "true".
+###############################
+# Toggle the two_phase to "true" before the COMMIT PREPARED.
+#
+# Since we are the special path for the case where both two_phase
+# and failover are altered, it is also set to "true".
+###############################
 $node_subscriber->safe_psql('postgres',
     "ALTER SUBSCRIPTION tap_sub_copy DISABLE;");
 $node_subscriber->poll_query_until('postgres',

diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index e021f87..58db97f 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -256,14 +256,15 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
      </para>
 
      <para>
-      The <literal>two_phase</literal> parameter can only be altered when the
-      subscription is disabled. When altering the parameter from <literal>true</literal>
+      The <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>
+      parameter can only be altered when the subscription is disabled.
+      When altering the parameter from <literal>true</literal>
       to <literal>false</literal>, the backend process checks for any incomplete
       prepared transactions done by the logical replication worker (from when
       <literal>two_phase</literal> parameter was still <literal>true</literal>)
-      and, if any are found, this command is failed with an error. In this
-      case, you can resolve prepared transactions on the publisher node or
-      manually roll back them on the subscriber. After the altering from
+      and, if any are found, an error is reported. If this happens, you can
+      resolve prepared transactions on the publisher node or
+      manually roll back them on the subscriber, then try again. After the altering from
       <literal>true</literal> to <literal>false</literal>, the publisher will
       replicate transactions again when they are committed.
      </para>

From 3bb372f1f02554f36738abc75e650cde79649c69 Mon Sep 17 00:00:00 2001
From: Ajin Cherian <ajinc@fast.au.fujitsu.com>
Date: Fri, 5 Apr 2024 06:47:18 -0400
Subject: [PATCH v19 1/3] Allow altering of two_phase option of a SUBSCRIPTION

This patch allows the user to alter the 'two_phase' option of a subscriber provided no
uncommitted prepared transactions are pending on that subscription.

Author: Cherian Ajin, Hayato Kuroda
---
 doc/src/sgml/protocol.sgml                    |  46 ++++--
 doc/src/sgml/ref/alter_subscription.sgml      |  12 +-
 src/backend/access/transam/twophase.c         |  72 ++++++++++
 src/backend/commands/subscriptioncmds.c       | 136 +++++++++++++-----
 .../libpqwalreceiver/libpqwalreceiver.c       |   9 +-
 src/backend/replication/logical/launcher.c    |  10 +-
 src/backend/replication/logical/worker.c      |  25 +---
 src/backend/replication/slot.c                |  44 ++++--
 src/backend/replication/walsender.c           |  32 +++--
 src/bin/psql/tab-complete.c                   |   2 +-
 src/include/access/twophase.h                 |   5 +
 src/include/replication/slot.h                |   3 +-
 src/include/replication/walreceiver.h         |  11 +-
 src/include/replication/worker_internal.h     |   3 +-
 src/test/regress/expected/subscription.out    |   5 +-
 src/test/regress/sql/subscription.sql         |   5 +-
 src/test/subscription/t/021_twophase.pl       |  86 ++++++++++-
 17 files changed, 376 insertions(+), 130 deletions(-)

diff --git a/doc/src/sgml/protocol.sgml b/doc/src/sgml/protocol.sgml
index 1b27d0a547..cba6661cf0 100644
--- a/doc/src/sgml/protocol.sgml
+++ b/doc/src/sgml/protocol.sgml
@@ -2049,21 +2049,6 @@ psql "dbname=postgres replication=database" -c "IDENTIFY_SYSTEM;"
       <para>The following options are supported:</para>
 
       <variablelist>
-       <varlistentry>
-        <term><literal>TWO_PHASE [ <replaceable class="parameter">boolean</replaceable> ]</literal></term>
-        <listitem>
-         <para>
-          If true, this logical replication slot supports decoding of two-phase
-          commit. With this option, commands related to two-phase commit such as
-          <literal>PREPARE TRANSACTION</literal>, <literal>COMMIT PREPARED</literal>
-          and <literal>ROLLBACK PREPARED</literal> are decoded and transmitted.
-          The transaction will be decoded and transmitted at
-          <literal>PREPARE TRANSACTION</literal> time.
-          The default is false.
-         </para>
-        </listitem>
-       </varlistentry>
-
        <varlistentry>
         <term><literal>RESERVE_WAL [ <replaceable class="parameter">boolean</replaceable> ]</literal></term>
         <listitem>
@@ -2104,6 +2089,21 @@ psql "dbname=postgres replication=database" -c "IDENTIFY_SYSTEM;"
          </para>
         </listitem>
        </varlistentry>
+
+       <varlistentry>
+        <term><literal>TWO_PHASE [ <replaceable class="parameter">boolean</replaceable> ]</literal></term>
+        <listitem>
+         <para>
+          If true, this logical replication slot supports decoding of two-phase
+          commit. With this option, commands related to two-phase commit such as
+          <literal>PREPARE TRANSACTION</literal>, <literal>COMMIT PREPARED</literal>
+          and <literal>ROLLBACK PREPARED</literal> are decoded and transmitted.
+          The transaction will be decoded and transmitted at
+          <literal>PREPARE TRANSACTION</literal> time.
+          The default is false.
+         </para>
+        </listitem>
+       </varlistentry>
       </variablelist>
 
       <para>
@@ -2206,6 +2206,22 @@ psql "dbname=postgres replication=database" -c "IDENTIFY_SYSTEM;"
        </varlistentry>
       </variablelist>
 
+      <variablelist>
+       <varlistentry>
+        <term><literal>TWO_PHASE [ <replaceable class="parameter">boolean</replaceable> ]</literal></term>
+        <listitem>
+         <para>
+          If true, this logical replication slot supports decoding of two-phase
+          commit. With this option, commands related to two-phase commit such as
+          <literal>PREPARE TRANSACTION</literal>, <literal>COMMIT PREPARED</literal>
+          and <literal>ROLLBACK PREPARED</literal> are decoded and transmitted.
+          The transaction will be decoded and transmitted at
+          <literal>PREPARE TRANSACTION</literal> time.
+         </para>
+        </listitem>
+       </varlistentry>
+      </variablelist>
+
      </listitem>
     </varlistentry>
 
diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index 476f195622..0b23df1b77 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -68,8 +68,9 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
   <para>
    Commands <command>ALTER SUBSCRIPTION ... REFRESH PUBLICATION</command>,
    <command>ALTER SUBSCRIPTION ... {SET|ADD|DROP} PUBLICATION ...</command>
-   with <literal>refresh</literal> option as <literal>true</literal> and
-   <command>ALTER SUBSCRIPTION ... SET (failover = true|false)</command>
+   with <literal>refresh</literal> option as <literal>true</literal>,
+   <command>ALTER SUBSCRIPTION ... SET (failover = true|false)</command> and
+   <command>ALTER SUBSCRIPTION ... SET (two_phase = true|false)</command>
    cannot be executed inside a transaction block.
 
    These commands also cannot be executed when the subscription has
@@ -228,9 +229,12 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-disable-on-error"><literal>disable_on_error</literal></link>,
       <link linkend="sql-createsubscription-params-with-password-required"><literal>password_required</literal></link>,
       <link linkend="sql-createsubscription-params-with-run-as-owner"><literal>run_as_owner</literal></link>,
-      <link linkend="sql-createsubscription-params-with-origin"><literal>origin</literal></link>, and
-      <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>.
+      <link linkend="sql-createsubscription-params-with-origin"><literal>origin</literal></link>,
+      <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>, and
+      <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>.
       Only a superuser can set <literal>password_required = false</literal>.
+      The <literal>two_phase</literal> parameter can only be altered when the
+      subscription is disabled.
      </para>
 
      <para>
diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index 9a8257fcaf..f7100306f7 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -2681,3 +2681,75 @@ LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 	LWLockRelease(TwoPhaseStateLock);
 	return found;
 }
+
+/*
+ * TwoPhaseTransactionGid
+ *		Form the prepared transaction GID for two_phase transactions.
+ *
+ * Return the GID in the supplied buffer.
+ */
+void
+TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid, int szgid)
+{
+	Assert(subid != InvalidRepOriginId);
+
+	if (!TransactionIdIsValid(xid))
+		ereport(ERROR,
+				(errcode(ERRCODE_PROTOCOL_VIOLATION),
+				 errmsg_internal("invalid two-phase transaction ID")));
+
+	snprintf(gid, szgid, "pg_gid_%u_%u", subid, xid);
+}
+
+/*
+ * IsTwoPhaseTransactionGidForSubid
+ *		Check whether the given GID (as formed by TwoPhaseTransactionGid) is
+ *		for the specified 'subid'.
+ */
+static bool
+IsTwoPhaseTransactionGidForSubid(Oid subid, char *gid)
+{
+	int			ret;
+	Oid			subid_written;
+	TransactionId xid;
+	char		gid_generated[GIDSIZE];
+
+	ret = sscanf(gid, "pg_gid_%u_%u", &subid_written, &xid);
+
+	/* Return false if the given GID has different format */
+	if (ret != 2 || subid != subid_written)
+		return false;
+
+	/* Construct the format GID based on the got xid */
+	TwoPhaseTransactionGid(subid, xid, gid_generated, sizeof(gid));
+
+	/* ...And check whether the given GID is exact same as the format GID */
+	return strcmp(gid, gid_generated) == 0;
+}
+
+/*
+ * LookupGXactBySubid
+ *		Check if the prepared transaction done by apply worker exists.
+ */
+bool
+LookupGXactBySubid(Oid subid)
+{
+	bool		found = false;
+
+	LWLockAcquire(TwoPhaseStateLock, LW_SHARED);
+	for (int i = 0; i < TwoPhaseState->numPrepXacts; i++)
+	{
+		GlobalTransaction gxact = TwoPhaseState->prepXacts[i];
+
+		/* Ignore not-yet-valid GIDs. */
+		if (gxact->valid &&
+			IsTwoPhaseTransactionGidForSubid(subid, gxact->gid))
+		{
+			found = true;
+			break;
+		}
+	}
+	LWLockRelease(TwoPhaseStateLock);
+
+	return found;
+}
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index 16d83b3253..a8e4faacbe 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -16,6 +16,7 @@
 
 #include "access/htup_details.h"
 #include "access/table.h"
+#include "access/twophase.h"
 #include "access/xact.h"
 #include "catalog/catalog.h"
 #include "catalog/dependency.h"
@@ -109,6 +110,8 @@ static void check_publications_origin(WalReceiverConn *wrconn,
 static void check_duplicates_in_publist(List *publist, Datum *datums);
 static List *merge_publications(List *oldpublist, List *newpublist, bool addpub, const char *subname);
 static void ReportSlotConnectionError(List *rstates, Oid subid, char *slotname, char *err);
+static void CheckAlterSubOption(Subscription *sub, const char *option,
+								bool isTopLevel);
 
 
 /*
@@ -259,21 +262,9 @@ parse_subscription_options(ParseState *pstate, List *stmt_options,
 			opts->specified_opts |= SUBOPT_STREAMING;
 			opts->streaming = defGetStreamingMode(defel);
 		}
-		else if (strcmp(defel->defname, "two_phase") == 0)
+		else if (IsSet(supported_opts, SUBOPT_TWOPHASE_COMMIT) &&
+				 strcmp(defel->defname, "two_phase") == 0)
 		{
-			/*
-			 * Do not allow toggling of two_phase option. Doing so could cause
-			 * missing of transactions and lead to an inconsistent replica.
-			 * See comments atop worker.c
-			 *
-			 * Note: Unsupported twophase indicates that this call originated
-			 * from AlterSubscription.
-			 */
-			if (!IsSet(supported_opts, SUBOPT_TWOPHASE_COMMIT))
-				ereport(ERROR,
-						(errcode(ERRCODE_SYNTAX_ERROR),
-						 errmsg("unrecognized subscription parameter: \"%s\"", defel->defname)));
-
 			if (IsSet(opts->specified_opts, SUBOPT_TWOPHASE_COMMIT))
 				errorConflictingDefElem(defel, pstate);
 
@@ -1079,6 +1070,47 @@ AlterSubscription_refresh(Subscription *sub, bool copy_data,
 		table_close(rel, NoLock);
 }
 
+/*
+ * Common checks for altering failover and two_phase option
+ */
+static void
+CheckAlterSubOption(Subscription *sub, const char *option, bool isTopLevel)
+{
+	StringInfoData cmd;
+
+	Assert(strcmp(option, "failover") == 0 ||
+		   strcmp(option, "two_phase") == 0);
+
+	if (!sub->slotname)
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("cannot set %s for a subscription that does not have a slot name",
+						option)));
+
+	/*
+	 * Do not allow changing the option if the subscription is enabled. This
+	 * is because both failover and two_phase options of the slot on the
+	 * publisher cannot be modified if the slot is currently acquired by the
+	 * apply worker.
+	 */
+	if (sub->enabled)
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("cannot set %s for enabled subscription",
+						option)));
+
+	initStringInfo(&cmd);
+	appendStringInfo(&cmd, "ALTER SUBSCRIPTION ... SET (%s)", option);
+
+	/*
+	 * The changed option of the slot can't be rolled back, so disallow if we
+	 * are in a transaction block.
+	 */
+	PreventInTransactionBlock(isTopLevel, cmd.data);
+
+	pfree(cmd.data);
+}
+
 /*
  * Alter the existing subscription.
  */
@@ -1145,7 +1177,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 			{
 				supported_opts = (SUBOPT_SLOT_NAME |
 								  SUBOPT_SYNCHRONOUS_COMMIT | SUBOPT_BINARY |
-								  SUBOPT_STREAMING | SUBOPT_DISABLE_ON_ERR |
+								  SUBOPT_STREAMING | SUBOPT_TWOPHASE_COMMIT |
+								  SUBOPT_DISABLE_ON_ERR |
 								  SUBOPT_PASSWORD_REQUIRED |
 								  SUBOPT_RUN_AS_OWNER | SUBOPT_FAILOVER |
 								  SUBOPT_ORIGIN);
@@ -1229,33 +1262,61 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 
 				if (IsSet(opts.specified_opts, SUBOPT_FAILOVER))
 				{
-					if (!sub->slotname)
+					CheckAlterSubOption(sub, "failover", isTopLevel);
+
+					values[Anum_pg_subscription_subfailover - 1] =
+						BoolGetDatum(opts.failover);
+					replaces[Anum_pg_subscription_subfailover - 1] = true;
+				}
+
+				if (IsSet(opts.specified_opts, SUBOPT_TWOPHASE_COMMIT))
+				{
+					CheckAlterSubOption(sub, "two_phase", isTopLevel);
+
+					/*
+					 * slot_name and two_phase cannot be altered
+					 * simultaneously. The latter part refers to the pre-set
+					 * slot name and tries to modify the slot option, so
+					 * changing both does not make sense.
+					 */
+					if (IsSet(opts.specified_opts, SUBOPT_SLOT_NAME))
 						ereport(ERROR,
-								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-								 errmsg("cannot set %s for a subscription that does not have a slot name",
-										"failover")));
+								(errcode(ERRCODE_SYNTAX_ERROR),
+								 errmsg("slot_name and two_phase cannot be altered at the same time")));
 
 					/*
-					 * Do not allow changing the failover state if the
-					 * subscription is enabled. This is because the failover
-					 * state of the slot on the publisher cannot be modified
-					 * if the slot is currently acquired by the apply worker.
+					 * Workers may still survive even if the subscription has
+					 * been disabled. They may read the pg_subscription
+					 * catalog and detect that the two_phase parameter is
+					 * updated, which causes an assertion failure that
+					 * two_phase should not be updated while the worker
+					 * exists. Ensure workers have already been exited to
+					 * avoid it.
 					 */
-					if (sub->enabled)
+					if (logicalrep_workers_find(subid, true, true))
 						ereport(ERROR,
 								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-								 errmsg("cannot set %s for enabled subscription",
-										"failover")));
+								 errmsg("cannot alter two_phase when logical replication worker is still running"),
+								 errhint("Wait certain time and try again.")));
 
 					/*
-					 * The changed failover option of the slot can't be rolled
-					 * back.
+					 * two_phase cannot be disabled if there are any
+					 * uncommitted prepared transactions present.
 					 */
-					PreventInTransactionBlock(isTopLevel, "ALTER SUBSCRIPTION ... SET (failover)");
-
-					values[Anum_pg_subscription_subfailover - 1] =
-						BoolGetDatum(opts.failover);
-					replaces[Anum_pg_subscription_subfailover - 1] = true;
+					if (!opts.twophase &&
+						sub->twophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
+						LookupGXactBySubid(subid))
+						ereport(ERROR,
+								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+								 errmsg("cannot disable two_phase when prepared transactions are present"),
+								 errhint("Resolve these transactions and try again.")));
+
+					/* Change system catalog accordingly */
+					values[Anum_pg_subscription_subtwophasestate - 1] =
+						CharGetDatum(opts.twophase ?
+									 LOGICALREP_TWOPHASE_STATE_PENDING :
+									 LOGICALREP_TWOPHASE_STATE_DISABLED);
+					replaces[Anum_pg_subscription_subtwophasestate - 1] = true;
 				}
 
 				if (IsSet(opts.specified_opts, SUBOPT_ORIGIN))
@@ -1507,7 +1568,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 	 * doing the database operations we won't be able to rollback altered
 	 * slot.
 	 */
-	if (replaces[Anum_pg_subscription_subfailover - 1])
+	if (replaces[Anum_pg_subscription_subfailover - 1] ||
+		replaces[Anum_pg_subscription_subtwophasestate - 1])
 	{
 		bool		must_use_password;
 		char	   *err;
@@ -1528,7 +1590,7 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 
 		PG_TRY();
 		{
-			walrcv_alter_slot(wrconn, sub->slotname, opts.failover);
+			walrcv_alter_slot(wrconn, sub->slotname, opts.failover, opts.twophase);
 		}
 		PG_FINALLY();
 		{
@@ -1675,9 +1737,7 @@ DropSubscription(DropSubscriptionStmt *stmt, bool isTopLevel)
 	 * New workers won't be started because we hold an exclusive lock on the
 	 * subscription till the end of the transaction.
 	 */
-	LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
-	subworkers = logicalrep_workers_find(subid, false);
-	LWLockRelease(LogicalRepWorkerLock);
+	subworkers = logicalrep_workers_find(subid, false, true);
 	foreach(lc, subworkers)
 	{
 		LogicalRepWorker *w = (LogicalRepWorker *) lfirst(lc);
diff --git a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
index 6c42c209d2..1cb601a148 100644
--- a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
+++ b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
@@ -80,7 +80,7 @@ static char *libpqrcv_create_slot(WalReceiverConn *conn,
 								  CRSSnapshotAction snapshot_action,
 								  XLogRecPtr *lsn);
 static void libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-								bool failover);
+								bool failover, bool two_phase);
 static pid_t libpqrcv_get_backend_pid(WalReceiverConn *conn);
 static WalRcvExecResult *libpqrcv_exec(WalReceiverConn *conn,
 									   const char *query,
@@ -1121,15 +1121,16 @@ libpqrcv_create_slot(WalReceiverConn *conn, const char *slotname,
  */
 static void
 libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-					bool failover)
+					bool failover, bool two_phase)
 {
 	StringInfoData cmd;
 	PGresult   *res;
 
 	initStringInfo(&cmd);
-	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( FAILOVER %s )",
+	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( FAILOVER %s, TWO_PHASE %s )",
 					 quote_identifier(slotname),
-					 failover ? "true" : "false");
+					 failover ? "true" : "false",
+					 two_phase ? "true" : "false");
 
 	res = libpqrcv_PQexec(conn->streamConn, cmd.data);
 	pfree(cmd.data);
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 27c3a91fb7..c566d50a07 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -272,11 +272,14 @@ logicalrep_worker_find(Oid subid, Oid relid, bool only_running)
  * the subscription, instead of just one.
  */
 List *
-logicalrep_workers_find(Oid subid, bool only_running)
+logicalrep_workers_find(Oid subid, bool only_running, bool acquire_lock)
 {
 	int			i;
 	List	   *res = NIL;
 
+	if (acquire_lock)
+		LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
+
 	Assert(LWLockHeldByMe(LogicalRepWorkerLock));
 
 	/* Search for attached worker for a given subscription id. */
@@ -288,6 +291,9 @@ logicalrep_workers_find(Oid subid, bool only_running)
 			res = lappend(res, w);
 	}
 
+	if (acquire_lock)
+		LWLockRelease(LogicalRepWorkerLock);
+
 	return res;
 }
 
@@ -759,7 +765,7 @@ logicalrep_worker_detach(void)
 
 		LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
 
-		workers = logicalrep_workers_find(MyLogicalRepWorker->subid, true);
+		workers = logicalrep_workers_find(MyLogicalRepWorker->subid, true, false);
 		foreach(lc, workers)
 		{
 			LogicalRepWorker *w = (LogicalRepWorker *) lfirst(lc);
diff --git a/src/backend/replication/logical/worker.c b/src/backend/replication/logical/worker.c
index c0bda6269b..6c798cd5b4 100644
--- a/src/backend/replication/logical/worker.c
+++ b/src/backend/replication/logical/worker.c
@@ -401,9 +401,6 @@ static void apply_handle_tuple_routing(ApplyExecutionData *edata,
 									   LogicalRepTupleData *newtup,
 									   CmdType operation);
 
-/* Compute GID for two_phase transactions */
-static void TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid, int szgid);
-
 /* Functions for skipping changes */
 static void maybe_start_skipping_changes(XLogRecPtr finish_lsn);
 static void stop_skipping_changes(void);
@@ -3911,7 +3908,7 @@ maybe_reread_subscription(void)
 	/* !slotname should never happen when enabled is true. */
 	Assert(newsub->slotname);
 
-	/* two-phase should not be altered */
+	/* two-phase cannot be altered while the worker exists */
 	Assert(newsub->twophasestate == MySubscription->twophasestate);
 
 	/*
@@ -4396,24 +4393,6 @@ cleanup_subxact_info()
 	subxact_data.nsubxacts_max = 0;
 }
 
-/*
- * Form the prepared transaction GID for two_phase transactions.
- *
- * Return the GID in the supplied buffer.
- */
-static void
-TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid, int szgid)
-{
-	Assert(subid != InvalidRepOriginId);
-
-	if (!TransactionIdIsValid(xid))
-		ereport(ERROR,
-				(errcode(ERRCODE_PROTOCOL_VIOLATION),
-				 errmsg_internal("invalid two-phase transaction ID")));
-
-	snprintf(gid, szgid, "pg_gid_%u_%u", subid, xid);
-}
-
 /*
  * Common function to run the apply loop with error handling. Disable the
  * subscription, if necessary.
@@ -5014,7 +4993,7 @@ AtEOXact_LogicalRepWorkers(bool isCommit)
 			List	   *workers;
 			ListCell   *lc2;
 
-			workers = logicalrep_workers_find(subid, true);
+			workers = logicalrep_workers_find(subid, true, false);
 			foreach(lc2, workers)
 			{
 				LogicalRepWorker *worker = (LogicalRepWorker *) lfirst(lc2);
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index baf9b89dc4..90494cb858 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -804,9 +804,12 @@ ReplicationSlotDrop(const char *name, bool nowait)
  * Change the definition of the slot identified by the specified name.
  */
 void
-ReplicationSlotAlter(const char *name, bool failover)
+ReplicationSlotAlter(const char *name, bool *failover, bool *two_phase)
 {
+	bool		update_slot = false;
+
 	Assert(MyReplicationSlot == NULL);
+	Assert(failover || two_phase);
 
 	ReplicationSlotAcquire(name, false);
 
@@ -832,28 +835,45 @@ ReplicationSlotAlter(const char *name, bool failover)
 		 * Do not allow users to enable failover on the standby as we do not
 		 * support sync to the cascading standby.
 		 */
-		if (failover)
+		if (failover && *failover)
 			ereport(ERROR,
 					errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 					errmsg("cannot enable failover for a replication slot"
 						   " on the standby"));
 	}
 
-	/*
-	 * Do not allow users to enable failover for temporary slots as we do not
-	 * support syncing temporary slots to the standby.
-	 */
-	if (failover && MyReplicationSlot->data.persistency == RS_TEMPORARY)
-		ereport(ERROR,
-				errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-				errmsg("cannot enable failover for a temporary replication slot"));
+	if (failover)
+	{
+		/*
+		 * Do not allow users to enable failover for temporary slots as we do
+		 * not support syncing temporary slots to the standby.
+		 */
+		if (*failover && MyReplicationSlot->data.persistency == RS_TEMPORARY)
+			ereport(ERROR,
+					errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+					errmsg("cannot enable failover for a temporary replication slot"));
+
+		if (MyReplicationSlot->data.failover != *failover)
+		{
+			SpinLockAcquire(&MyReplicationSlot->mutex);
+			MyReplicationSlot->data.failover = *failover;
+			SpinLockRelease(&MyReplicationSlot->mutex);
+
+			update_slot = true;
+		}
+	}
 
-	if (MyReplicationSlot->data.failover != failover)
+	if (two_phase && MyReplicationSlot->data.two_phase != *two_phase)
 	{
 		SpinLockAcquire(&MyReplicationSlot->mutex);
-		MyReplicationSlot->data.failover = failover;
+		MyReplicationSlot->data.two_phase = *two_phase;
 		SpinLockRelease(&MyReplicationSlot->mutex);
 
+		update_slot = true;
+	}
+
+	if (update_slot)
+	{
 		ReplicationSlotMarkDirty();
 		ReplicationSlotSave();
 	}
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 2d1a9ec900..9b40b1cf7d 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1407,12 +1407,15 @@ DropReplicationSlot(DropReplicationSlotCmd *cmd)
 }
 
 /*
- * Process extra options given to ALTER_REPLICATION_SLOT.
+ * Change the definition of a replication slot.
  */
 static void
-ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd, bool *failover)
+AlterReplicationSlot(AlterReplicationSlotCmd *cmd)
 {
 	bool		failover_given = false;
+	bool		two_phase_given = false;
+	bool		failover;
+	bool		two_phase;
 
 	/* Parse options */
 	foreach_ptr(DefElem, defel, cmd->options)
@@ -1424,23 +1427,24 @@ ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd, bool *failover)
 						(errcode(ERRCODE_SYNTAX_ERROR),
 						 errmsg("conflicting or redundant options")));
 			failover_given = true;
-			*failover = defGetBoolean(defel);
+			failover = defGetBoolean(defel);
+		}
+		else if (strcmp(defel->defname, "two_phase") == 0)
+		{
+			if (two_phase_given)
+				ereport(ERROR,
+						(errcode(ERRCODE_SYNTAX_ERROR),
+						 errmsg("conflicting or redundant options")));
+			two_phase_given = true;
+			two_phase = defGetBoolean(defel);
 		}
 		else
 			elog(ERROR, "unrecognized option: %s", defel->defname);
 	}
-}
-
-/*
- * Change the definition of a replication slot.
- */
-static void
-AlterReplicationSlot(AlterReplicationSlotCmd *cmd)
-{
-	bool		failover = false;
 
-	ParseAlterReplSlotOptions(cmd, &failover);
-	ReplicationSlotAlter(cmd->slotname, failover);
+	ReplicationSlotAlter(cmd->slotname,
+						 failover_given ? &failover : NULL,
+						 two_phase_given ? &two_phase : NULL);
 }
 
 /*
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
index d453e224d9..891face1b6 100644
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -1948,7 +1948,7 @@ psql_completion(const char *text, int start, int end)
 	else if (HeadMatches("ALTER", "SUBSCRIPTION", MatchAny) && TailMatches("SET", "("))
 		COMPLETE_WITH("binary", "disable_on_error", "failover", "origin",
 					  "password_required", "run_as_owner", "slot_name",
-					  "streaming", "synchronous_commit");
+					  "streaming", "synchronous_commit", "two_phase");
 	/* ALTER SUBSCRIPTION <name> SKIP ( */
 	else if (HeadMatches("ALTER", "SUBSCRIPTION", MatchAny) && TailMatches("SKIP", "("))
 		COMPLETE_WITH("lsn");
diff --git a/src/include/access/twophase.h b/src/include/access/twophase.h
index 56248c0006..d37e06fdee 100644
--- a/src/include/access/twophase.h
+++ b/src/include/access/twophase.h
@@ -62,4 +62,9 @@ extern void PrepareRedoRemove(TransactionId xid, bool giveWarning);
 extern void restoreTwoPhaseData(void);
 extern bool LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 						TimestampTz origin_prepare_timestamp);
+
+extern void TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid,
+								   int szgid);
+extern bool LookupGXactBySubid(Oid subid);
+
 #endif							/* TWOPHASE_H */
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index c9675ee87c..cde164472a 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -243,7 +243,8 @@ extern void ReplicationSlotCreate(const char *name, bool db_specific,
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
 extern void ReplicationSlotDropAcquired(void);
-extern void ReplicationSlotAlter(const char *name, bool failover);
+extern void ReplicationSlotAlter(const char *name, bool *failover,
+								 bool *two_phase);
 
 extern void ReplicationSlotAcquire(const char *name, bool nowait);
 extern void ReplicationSlotRelease(void);
diff --git a/src/include/replication/walreceiver.h b/src/include/replication/walreceiver.h
index 12f71fa99b..31fa1257ec 100644
--- a/src/include/replication/walreceiver.h
+++ b/src/include/replication/walreceiver.h
@@ -372,12 +372,13 @@ typedef char *(*walrcv_create_slot_fn) (WalReceiverConn *conn,
 /*
  * walrcv_alter_slot_fn
  *
- * Change the definition of a replication slot. Currently, it only supports
- * changing the failover property of the slot.
+ * Change the definition of a replication slot. Currently, it supports
+ * changing the failover and the two_phase property of the slot.
  */
 typedef void (*walrcv_alter_slot_fn) (WalReceiverConn *conn,
 									  const char *slotname,
-									  bool failover);
+									  bool failover,
+									  bool two_phase);
 
 /*
  * walrcv_get_backend_pid_fn
@@ -455,8 +456,8 @@ extern PGDLLIMPORT WalReceiverFunctionsType *WalReceiverFunctions;
 	WalReceiverFunctions->walrcv_send(conn, buffer, nbytes)
 #define walrcv_create_slot(conn, slotname, temporary, two_phase, failover, snapshot_action, lsn) \
 	WalReceiverFunctions->walrcv_create_slot(conn, slotname, temporary, two_phase, failover, snapshot_action, lsn)
-#define walrcv_alter_slot(conn, slotname, failover) \
-	WalReceiverFunctions->walrcv_alter_slot(conn, slotname, failover)
+#define walrcv_alter_slot(conn, slotname, failover, two_phase) \
+	WalReceiverFunctions->walrcv_alter_slot(conn, slotname, failover, two_phase)
 #define walrcv_get_backend_pid(conn) \
 	WalReceiverFunctions->walrcv_get_backend_pid(conn)
 #define walrcv_exec(conn, exec, nRetTypes, retTypes) \
diff --git a/src/include/replication/worker_internal.h b/src/include/replication/worker_internal.h
index 515aefd519..9646261d7e 100644
--- a/src/include/replication/worker_internal.h
+++ b/src/include/replication/worker_internal.h
@@ -240,7 +240,8 @@ extern PGDLLIMPORT bool InitializingApplyWorker;
 extern void logicalrep_worker_attach(int slot);
 extern LogicalRepWorker *logicalrep_worker_find(Oid subid, Oid relid,
 												bool only_running);
-extern List *logicalrep_workers_find(Oid subid, bool only_running);
+extern List *logicalrep_workers_find(Oid subid, bool only_running,
+									 bool acquire_lock);
 extern bool logicalrep_worker_launch(LogicalRepWorkerType wtype,
 									 Oid dbid, Oid subid, const char *subname,
 									 Oid userid, Oid relid,
diff --git a/src/test/regress/expected/subscription.out b/src/test/regress/expected/subscription.out
index 5c2f1ee517..17d48b1685 100644
--- a/src/test/regress/expected/subscription.out
+++ b/src/test/regress/expected/subscription.out
@@ -377,10 +377,7 @@ HINT:  To initiate replication, you must manually create the replication slot, e
  regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | p                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
---fail - alter of two_phase option not supported.
-ALTER SUBSCRIPTION regress_testsub SET (two_phase = false);
-ERROR:  unrecognized subscription parameter: "two_phase"
--- but can alter streaming when two_phase enabled
+-- we can alter streaming when two_phase enabled
 ALTER SUBSCRIPTION regress_testsub SET (streaming = true);
 \dRs+
                                                                                                                 List of subscriptions
diff --git a/src/test/regress/sql/subscription.sql b/src/test/regress/sql/subscription.sql
index 3e5ba4cb8c..007c9e7037 100644
--- a/src/test/regress/sql/subscription.sql
+++ b/src/test/regress/sql/subscription.sql
@@ -256,10 +256,7 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUBLICATION testpub WITH (connect = false, two_phase = true);
 
 \dRs+
---fail - alter of two_phase option not supported.
-ALTER SUBSCRIPTION regress_testsub SET (two_phase = false);
-
--- but can alter streaming when two_phase enabled
+-- we can alter streaming when two_phase enabled
 ALTER SUBSCRIPTION regress_testsub SET (streaming = true);
 
 \dRs+
diff --git a/src/test/subscription/t/021_twophase.pl b/src/test/subscription/t/021_twophase.pl
index 9437cd4c3b..66265c729f 100644
--- a/src/test/subscription/t/021_twophase.pl
+++ b/src/test/subscription/t/021_twophase.pl
@@ -367,6 +367,90 @@ $result =
   $node_subscriber->safe_psql('postgres', "SELECT count(*) FROM tab_copy;");
 is($result, qq(2), 'replicated data in subscriber table');
 
+# Clean up
+$node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub");
+
+###############################
+# Alter the subscription to two_phase = false.
+# Verify that the altered subscription reflects the two_phase option.
+###############################
+
+# Alter subscription two_phase to false
+$node_subscriber->safe_psql('postgres',
+    "ALTER SUBSCRIPTION tap_sub_copy DISABLE;");
+$node_subscriber->poll_query_until('postgres',
+    "SELECT count(*) = 0 FROM pg_stat_activity WHERE backend_type = 'logical replication worker'"
+);
+$node_subscriber->safe_psql(
+	'postgres', "
+    ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = false);
+    ALTER SUBSCRIPTION tap_sub_copy ENABLE;");
+
+# Wait for subscription startup
+$node_subscriber->wait_for_subscription_sync($node_publisher, $appname_copy);
+
+# Make sure that the two-phase is disabled on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT subtwophasestate FROM pg_subscription WHERE subname = 'tap_sub_copy';"
+);
+is($result, qq(d), 'two-phase should be disabled');
+
+###############################
+# Now do a prepare on the publisher.
+# Verify that it is not replicated.
+###############################
+$node_publisher->safe_psql(
+	'postgres', qq{
+    BEGIN;
+    INSERT INTO tab_copy VALUES (100);
+    PREPARE TRANSACTION 'newgid';
+	});
+
+# Wait for the subscriber to catchup
+$node_publisher->wait_for_catchup($appname_copy);
+
+# Make sure there are no prepared transactions on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT count(*) FROM pg_prepared_xacts;");
+is($result, qq(0), 'should be no prepared transactions on subscriber');
+
+###############################
+# Now commit the insert.
+# Verify that it is replicated.
+###############################
+$node_publisher->safe_psql('postgres', "COMMIT PREPARED 'newgid';");
+
+# Wait for the subscriber to catchup
+$node_publisher->wait_for_catchup($appname_copy);
+
+# Make sure that the committed transaction is replicated.
+$result =
+  $node_subscriber->safe_psql('postgres', "SELECT count(*) FROM tab_copy;");
+is($result, qq(3), 'replicated data in subscriber table');
+
+###############################
+# Alter the subscription to two_phase = true.
+# Verify that the altered subscription reflects the two_phase option.
+###############################
+$node_subscriber->safe_psql('postgres',
+    "ALTER SUBSCRIPTION tap_sub_copy DISABLE;");
+$node_subscriber->poll_query_until('postgres',
+    "SELECT count(*) = 0 FROM pg_stat_activity WHERE backend_type = 'logical replication worker'"
+);
+$node_subscriber->safe_psql(
+	'postgres', "
+    ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = true);
+    ALTER SUBSCRIPTION tap_sub_copy ENABLE;");
+
+# Wait for subscription startup
+$node_subscriber->wait_for_subscription_sync($node_publisher, $appname_copy);
+
+# Make sure that the two-phase is enabled on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT subtwophasestate FROM pg_subscription WHERE subname = 'tap_sub_copy';"
+);
+is($result, qq(e), 'two-phase should be enabled');
+
 $node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub_copy;");
 $node_publisher->safe_psql('postgres', "DROP PUBLICATION tap_pub_copy;");
 
@@ -374,8 +458,6 @@ $node_publisher->safe_psql('postgres', "DROP PUBLICATION tap_pub_copy;");
 # check all the cleanup
 ###############################
 
-$node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub");
-
 $result = $node_subscriber->safe_psql('postgres',
 	"SELECT count(*) FROM pg_subscription");
 is($result, qq(0), 'check subscription was dropped on subscriber');
-- 
2.43.0

From 1fef6db98d4bc479c75f2ac5bebae4c659617a1c Mon Sep 17 00:00:00 2001
From: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Date: Wed, 17 Apr 2024 06:18:23 +0000
Subject: [PATCH v19 2/3] Alter slot option two_phase only when altering "true"
 to "false"

Since the two_phase option is controlled by both the publisher (as a slot option)
and the subscriber (as a subscription option), the slot option must also be
modified.

Regarding the false->true case, the backend process alters the subtwophase to
LOGICALREP_TWOPHASE_STATE_PENDING once. After the subscription is enabled, a new
logical replication worker requests to change the two_phase option of its slot
from pending to true after the initial data synchronization is done. The code
path is the same as the case in which two_phase is initially set to true, so
there is no need to do something remarkable. However, for the true->false case,
the backend must connect to the publisher and expressly change the parameter
because the apply worker does not alter the option to false. Because this
operation cannot be rolled back, altering the two_phase parameter from "true"
to "false" within a transaction is prohibited.
---
 doc/src/sgml/ref/alter_subscription.sgml      |  2 +-
 src/backend/commands/subscriptioncmds.c       | 84 ++++++++++++++-----
 .../libpqwalreceiver/libpqwalreceiver.c       | 23 +++--
 src/include/replication/walreceiver.h         |  5 +-
 src/test/subscription/t/021_twophase.pl       | 47 +++++++----
 5 files changed, 112 insertions(+), 49 deletions(-)

diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index 0b23df1b77..df44415661 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -70,7 +70,7 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
    <command>ALTER SUBSCRIPTION ... {SET|ADD|DROP} PUBLICATION ...</command>
    with <literal>refresh</literal> option as <literal>true</literal>,
    <command>ALTER SUBSCRIPTION ... SET (failover = true|false)</command> and
-   <command>ALTER SUBSCRIPTION ... SET (two_phase = true|false)</command>
+   <command>ALTER SUBSCRIPTION ... SET (two_phase = false)</command>
    cannot be executed inside a transaction block.
 
    These commands also cannot be executed when the subscription has
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index a8e4faacbe..9fed49f88c 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -111,7 +111,7 @@ static void check_duplicates_in_publist(List *publist, Datum *datums);
 static List *merge_publications(List *oldpublist, List *newpublist, bool addpub, const char *subname);
 static void ReportSlotConnectionError(List *rstates, Oid subid, char *slotname, char *err);
 static void CheckAlterSubOption(Subscription *sub, const char *option,
-								bool isTopLevel);
+								bool slot_needs_update, bool isTopLevel);
 
 
 /*
@@ -1074,14 +1074,18 @@ AlterSubscription_refresh(Subscription *sub, bool copy_data,
  * Common checks for altering failover and two_phase option
  */
 static void
-CheckAlterSubOption(Subscription *sub, const char *option, bool isTopLevel)
+CheckAlterSubOption(Subscription *sub, const char *option,
+					bool slot_needs_update, bool isTopLevel)
 {
-	StringInfoData cmd;
-
 	Assert(strcmp(option, "failover") == 0 ||
 		   strcmp(option, "two_phase") == 0);
 
-	if (!sub->slotname)
+	/*
+	 * If the slot needs to be updated, the backend must connect to the
+	 * publisher and request the alteration. slot_name must be required at that
+	 * time.
+	 */
+	if (slot_needs_update && !sub->slotname)
 		ereport(ERROR,
 				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
 				 errmsg("cannot set %s for a subscription that does not have a slot name",
@@ -1099,16 +1103,20 @@ CheckAlterSubOption(Subscription *sub, const char *option, bool isTopLevel)
 				 errmsg("cannot set %s for enabled subscription",
 						option)));
 
-	initStringInfo(&cmd);
-	appendStringInfo(&cmd, "ALTER SUBSCRIPTION ... SET (%s)", option);
-
 	/*
 	 * The changed option of the slot can't be rolled back, so disallow if we
 	 * are in a transaction block.
 	 */
-	PreventInTransactionBlock(isTopLevel, cmd.data);
+	if (slot_needs_update)
+	{
+		StringInfoData cmd;
 
-	pfree(cmd.data);
+		initStringInfo(&cmd);
+		appendStringInfo(&cmd, "ALTER SUBSCRIPTION ... SET (%s)", option);
+
+		PreventInTransactionBlock(isTopLevel, cmd.data);
+		pfree(cmd.data);
+	}
 }
 
 /*
@@ -1130,6 +1138,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 	Form_pg_subscription form;
 	bits32		supported_opts;
 	SubOpts		opts = {0};
+	bool		update_failover = false;
+	bool		update_two_phase = false;
 
 	rel = table_open(SubscriptionRelationId, RowExclusiveLock);
 
@@ -1262,7 +1272,16 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 
 				if (IsSet(opts.specified_opts, SUBOPT_FAILOVER))
 				{
-					CheckAlterSubOption(sub, "failover", isTopLevel);
+					/*
+					 * First, mark the needs to alter the replication slot.
+					 * Failover option is controlled by both the publisher (as
+					 * a slot option) and the subscriber (as a subscription
+					 * option).
+					 */
+					update_failover = true;
+
+					CheckAlterSubOption(sub, "failover", update_failover,
+										isTopLevel);
 
 					values[Anum_pg_subscription_subfailover - 1] =
 						BoolGetDatum(opts.failover);
@@ -1271,15 +1290,35 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 
 				if (IsSet(opts.specified_opts, SUBOPT_TWOPHASE_COMMIT))
 				{
-					CheckAlterSubOption(sub, "two_phase", isTopLevel);
+					/*
+					 * First, check the need to alter the replication slot.
+					 * Two_phase option is controlled by both the publisher
+					 * (as a slot option) and the subscriber (as a
+					 * subscription option). The slot option must be altered
+					 * only when changing "true" to "false".
+					 *
+					 * There is no need to do something remarkable regarding
+					 * the "false" to "true" case; the backend process alters
+					 * subtwophase to LOGICALREP_TWOPHASE_STATE_PENDING once.
+					 * After the subscription is enabled, a new logical
+					 * replication worker requests to change the two_phase
+					 * option of its slot from pending to true when the
+					 * initial data synchronization is done. The code path is
+					 * the same as the case in which two_phase is initially
+					 * set to true.
+					 */
+					update_two_phase = !opts.twophase;
+
+					CheckAlterSubOption(sub, "two_phase", update_two_phase,
+										isTopLevel);
 
 					/*
-					 * slot_name and two_phase cannot be altered
-					 * simultaneously. The latter part refers to the pre-set
-					 * slot name and tries to modify the slot option, so
-					 * changing both does not make sense.
+					 * Modifying the two_phase slot option requires a slot
+					 * lookup by slot name, so changing the slot name
+					 * at the same time is not allowed.
 					 */
-					if (IsSet(opts.specified_opts, SUBOPT_SLOT_NAME))
+					if (update_two_phase &&
+						IsSet(opts.specified_opts, SUBOPT_SLOT_NAME))
 						ereport(ERROR,
 								(errcode(ERRCODE_SYNTAX_ERROR),
 								 errmsg("slot_name and two_phase cannot be altered at the same time")));
@@ -1303,7 +1342,7 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 					 * two_phase cannot be disabled if there are any
 					 * uncommitted prepared transactions present.
 					 */
-					if (!opts.twophase &&
+					if (update_two_phase &&
 						sub->twophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
 						LookupGXactBySubid(subid))
 						ereport(ERROR,
@@ -1562,14 +1601,13 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 	}
 
 	/*
-	 * Try to acquire the connection necessary for altering slot.
+	 * Try to acquire the connection necessary for altering slot, if needed.
 	 *
 	 * This has to be at the end because otherwise if there is an error while
 	 * doing the database operations we won't be able to rollback altered
 	 * slot.
 	 */
-	if (replaces[Anum_pg_subscription_subfailover - 1] ||
-		replaces[Anum_pg_subscription_subtwophasestate - 1])
+	if (update_failover || update_two_phase)
 	{
 		bool		must_use_password;
 		char	   *err;
@@ -1590,7 +1628,9 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 
 		PG_TRY();
 		{
-			walrcv_alter_slot(wrconn, sub->slotname, opts.failover, opts.twophase);
+			walrcv_alter_slot(wrconn, sub->slotname,
+							  update_failover ? &opts.failover : NULL,
+							  update_two_phase ? &opts.twophase : NULL);
 		}
 		PG_FINALLY();
 		{
diff --git a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
index 1cb601a148..97f957cd87 100644
--- a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
+++ b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
@@ -80,7 +80,7 @@ static char *libpqrcv_create_slot(WalReceiverConn *conn,
 								  CRSSnapshotAction snapshot_action,
 								  XLogRecPtr *lsn);
 static void libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-								bool failover, bool two_phase);
+								const bool *failover, const bool *two_phase);
 static pid_t libpqrcv_get_backend_pid(WalReceiverConn *conn);
 static WalRcvExecResult *libpqrcv_exec(WalReceiverConn *conn,
 									   const char *query,
@@ -1121,16 +1121,27 @@ libpqrcv_create_slot(WalReceiverConn *conn, const char *slotname,
  */
 static void
 libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-					bool failover, bool two_phase)
+					const bool *failover, const bool *two_phase)
 {
 	StringInfoData cmd;
 	PGresult   *res;
 
 	initStringInfo(&cmd);
-	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( FAILOVER %s, TWO_PHASE %s )",
-					 quote_identifier(slotname),
-					 failover ? "true" : "false",
-					 two_phase ? "true" : "false");
+	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( ",
+					 quote_identifier(slotname));
+
+	if (failover)
+		appendStringInfo(&cmd, "FAILOVER %s",
+						 *failover ? "true" : "false");
+
+	if (failover && two_phase)
+		appendStringInfo(&cmd, ", ");
+
+	if (two_phase)
+		appendStringInfo(&cmd, "TWO_PHASE %s",
+						 *two_phase ? "true" : "false");
+
+	appendStringInfoString(&cmd, " );");
 
 	res = libpqrcv_PQexec(conn->streamConn, cmd.data);
 	pfree(cmd.data);
diff --git a/src/include/replication/walreceiver.h b/src/include/replication/walreceiver.h
index 31fa1257ec..7ffa5a58b3 100644
--- a/src/include/replication/walreceiver.h
+++ b/src/include/replication/walreceiver.h
@@ -377,8 +377,9 @@ typedef char *(*walrcv_create_slot_fn) (WalReceiverConn *conn,
  */
 typedef void (*walrcv_alter_slot_fn) (WalReceiverConn *conn,
 									  const char *slotname,
-									  bool failover,
-									  bool two_phase);
+									  const bool *failover,
+									  const bool *two_phase);
+
 
 /*
  * walrcv_get_backend_pid_fn
diff --git a/src/test/subscription/t/021_twophase.pl b/src/test/subscription/t/021_twophase.pl
index 66265c729f..c8fb3b7f17 100644
--- a/src/test/subscription/t/021_twophase.pl
+++ b/src/test/subscription/t/021_twophase.pl
@@ -375,6 +375,12 @@ $node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub");
 # Verify that the altered subscription reflects the two_phase option.
 ###############################
 
+# Confirm two-phase slot option is enabled before altering
+$result = $node_publisher->safe_psql('postgres',
+	"SELECT two_phase FROM pg_replication_slots WHERE slot_name = 'tap_sub_copy';"
+);
+is($result, qq(t), 'two-phase is enabled');
+
 # Alter subscription two_phase to false
 $node_subscriber->safe_psql('postgres',
     "ALTER SUBSCRIPTION tap_sub_copy DISABLE;");
@@ -393,7 +399,13 @@ $node_subscriber->wait_for_subscription_sync($node_publisher, $appname_copy);
 $result = $node_subscriber->safe_psql('postgres',
 	"SELECT subtwophasestate FROM pg_subscription WHERE subname = 'tap_sub_copy';"
 );
-is($result, qq(d), 'two-phase should be disabled');
+is($result, qq(d), 'two-phase subscription option should be disabled');
+
+# Make sure that the two-phase slot option is also disabled
+$result = $node_publisher->safe_psql('postgres',
+	"SELECT two_phase FROM pg_replication_slots WHERE slot_name = 'tap_sub_copy';"
+);
+is($result, qq(f), 'two-phase slot option should be disabled');
 
 ###############################
 # Now do a prepare on the publisher.
@@ -414,6 +426,22 @@ $result = $node_subscriber->safe_psql('postgres',
 	"SELECT count(*) FROM pg_prepared_xacts;");
 is($result, qq(0), 'should be no prepared transactions on subscriber');
 
+###############################
+# Toggle the two_phase to "true" before the COMMIT PREPARED.
+#
+# Since we are the special path for the case where both two_phase
+# and failover are altered, it is also set to "true".
+###############################
+$node_subscriber->safe_psql('postgres',
+    "ALTER SUBSCRIPTION tap_sub_copy DISABLE;");
+$node_subscriber->poll_query_until('postgres',
+    "SELECT count(*) = 0 FROM pg_stat_activity WHERE backend_type = 'logical replication worker'"
+);
+$node_subscriber->safe_psql(
+	'postgres', "
+    ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = true, failover = true);
+    ALTER SUBSCRIPTION tap_sub_copy ENABLE;");
+
 ###############################
 # Now commit the insert.
 # Verify that it is replicated.
@@ -428,23 +456,6 @@ $result =
   $node_subscriber->safe_psql('postgres', "SELECT count(*) FROM tab_copy;");
 is($result, qq(3), 'replicated data in subscriber table');
 
-###############################
-# Alter the subscription to two_phase = true.
-# Verify that the altered subscription reflects the two_phase option.
-###############################
-$node_subscriber->safe_psql('postgres',
-    "ALTER SUBSCRIPTION tap_sub_copy DISABLE;");
-$node_subscriber->poll_query_until('postgres',
-    "SELECT count(*) = 0 FROM pg_stat_activity WHERE backend_type = 'logical replication worker'"
-);
-$node_subscriber->safe_psql(
-	'postgres', "
-    ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = true);
-    ALTER SUBSCRIPTION tap_sub_copy ENABLE;");
-
-# Wait for subscription startup
-$node_subscriber->wait_for_subscription_sync($node_publisher, $appname_copy);
-
 # Make sure that the two-phase is enabled on the subscriber
 $result = $node_subscriber->safe_psql('postgres',
 	"SELECT subtwophasestate FROM pg_subscription WHERE subname = 'tap_sub_copy';"
-- 
2.43.0

From 34cd7afbeafb90da3c65a71cf12362c980019061 Mon Sep 17 00:00:00 2001
From: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Date: Tue, 9 Jul 2024 08:01:43 +0000
Subject: [PATCH v19 3/3] Notify users to roll back prepared transactions

---
 doc/src/sgml/ref/alter_subscription.sgml | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index df44415661..58db97f415 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -233,8 +233,6 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>, and
       <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>.
       Only a superuser can set <literal>password_required = false</literal>.
-      The <literal>two_phase</literal> parameter can only be altered when the
-      subscription is disabled.
      </para>
 
      <para>
@@ -256,6 +254,20 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>
       option is enabled.
      </para>
+
+     <para>
+      The <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>
+      parameter can only be altered when the subscription is disabled.
+      When altering the parameter from <literal>true</literal>
+      to <literal>false</literal>, the backend process checks for any incomplete
+      prepared transactions done by the logical replication worker (from when
+      <literal>two_phase</literal> parameter was still <literal>true</literal>)
+      and, if any are found, an error is reported. If this happens, you can
+      resolve prepared transactions on the publisher node or
+      manually roll back them on the subscriber, then try again. After the altering from
+      <literal>true</literal> to <literal>false</literal>, the publisher will
+      replicate transactions again when they are committed.
+     </para>
     </listitem>
    </varlistentry>
 
-- 
2.43.0

diff --git a/doc/src/sgml/protocol.sgml b/doc/src/sgml/protocol.sgml
index cba6661..24c57fb 100644
--- a/doc/src/sgml/protocol.sgml
+++ b/doc/src/sgml/protocol.sgml
@@ -2192,7 +2192,7 @@ psql "dbname=postgres replication=database" -c "IDENTIFY_SYSTEM;"
        </varlistentry>
       </variablelist>
 
-      <para>The following option is supported:</para>
+      <para>The following options are supported:</para>
 
       <variablelist>
        <varlistentry>
diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index f710030..b426f0b 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -2689,7 +2689,7 @@ LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
  * Return the GID in the supplied buffer.
  */
 void
-TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid, int szgid)
+TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid_res, int szgid)
 {
 	Assert(subid != InvalidRepOriginId);
 
@@ -2698,7 +2698,7 @@ TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid, int szgid)
 				(errcode(ERRCODE_PROTOCOL_VIOLATION),
 				 errmsg_internal("invalid two-phase transaction ID")));
 
-	snprintf(gid, szgid, "pg_gid_%u_%u", subid, xid);
+	snprintf(gid_res, szgid, "pg_gid_%u_%u", subid, xid);
 }
 
 /*
@@ -2710,20 +2710,26 @@ static bool
 IsTwoPhaseTransactionGidForSubid(Oid subid, char *gid)
 {
 	int			ret;
-	Oid			subid_written;
-	TransactionId xid;
+	Oid			subid_from_gid;
+	TransactionId xid_from_gid;
 	char		gid_generated[GIDSIZE];
 
-	ret = sscanf(gid, "pg_gid_%u_%u", &subid_written, &xid);
+	/* Extract the subid and xid from the given GID. */
+	ret = sscanf(gid, "pg_gid_%u_%u", &subid_from_gid, &xid_from_gid);
 
-	/* Return false if the given GID has different format */
-	if (ret != 2 || subid != subid_written)
+	/*
+	 * Check that the given GID has expected format, and at least the subid
+	 * matches.
+	 */
+	if (ret != 2 || subid != subid_from_gid)
 		return false;
 
-	/* Construct the format GID based on the got xid */
-	TwoPhaseTransactionGid(subid, xid, gid_generated, sizeof(gid));
-
-	/* ...And check whether the given GID is exact same as the format GID */
+	/*
+	 * Reconstruct a tmp GID based on the subid and xid extracted from
+	 * the given GID. Check that the tmp GID and the given GID match.
+	 */
+	TwoPhaseTransactionGid(subid_from_gid, xid_from_gid,
+						   gid_generated, sizeof(gid_generated));
 	return strcmp(gid, gid_generated) == 0;
 }
 

diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index f770e9c..a826be9 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -1079,17 +1079,6 @@ CheckAlterSubOption(Subscription *sub, const char *option,
 		   strcmp(option, "two_phase") == 0);
 
 	/*
-	 * If the slot needs to be updated, the backend must connect to the
-	 * publisher and request the alteration. slot_name must be required at that
-	 * time.
-	 */
-	if (slot_needs_update && !sub->slotname)
-		ereport(ERROR,
-				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-				 errmsg("cannot set %s for a subscription that does not have a slot name",
-						option)));
-
-	/*
 	 * Do not allow changing the option if the subscription is enabled. This
 	 * is because both failover and two_phase options of the slot on the
 	 * publisher cannot be modified if the slot is currently acquired by the
@@ -1101,17 +1090,27 @@ CheckAlterSubOption(Subscription *sub, const char *option,
 				 errmsg("cannot set %s for enabled subscription",
 						option)));
 
-	/*
-	 * The changed option of the slot can't be rolled back, so disallow if we
-	 * are in a transaction block.
-	 */
 	if (slot_needs_update)
 	{
 		StringInfoData cmd;
 
+		/*
+		 * If the slot needs to be updated, the backend must connect to the
+		 * publisher and request the alteration. A slot_name is required at
+		 * that time.
+		 */
+		if (!sub->slotname)
+			ereport(ERROR,
+					(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+					 errmsg("cannot set %s for a subscription that does not have a slot name",
+							option)));
+
+		/*
+		 * The changed option of the slot can't be rolled back, so disallow if we
+		 * are in a transaction block.
+		 */
 		initStringInfo(&cmd);
 		appendStringInfo(&cmd, "ALTER SUBSCRIPTION ... SET (%s)", option);
-
 		PreventInTransactionBlock(isTopLevel, cmd.data);
 		pfree(cmd.data);
 	}
@@ -1132,12 +1131,12 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 	HeapTuple	tup;
 	Oid			subid;
 	bool		update_tuple = false;
+	bool		update_failover = false;
+	bool		update_two_phase = false;
 	Subscription *sub;
 	Form_pg_subscription form;
 	bits32		supported_opts;
 	SubOpts		opts = {0};
-	bool		update_failover = false;
-	bool		update_two_phase = false;
 
 	rel = table_open(SubscriptionRelationId, RowExclusiveLock);
 
@@ -1271,7 +1270,7 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 				if (IsSet(opts.specified_opts, SUBOPT_FAILOVER))
 				{
 					/*
-					 * First, mark the needs to alter the replication slot.
+					 * First, mark the need to alter the replication slot.
 					 * Failover option is controlled by both the publisher (as
 					 * a slot option) and the subscriber (as a subscription
 					 * option).
@@ -1295,15 +1294,14 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 					 * subscription option). The slot option must be altered
 					 * only when changing "true" to "false".
 					 *
-					 * There is no need to do something remarkable regarding
+					 * There is no need to do anything remarkable for
 					 * the "false" to "true" case; the backend process alters
 					 * subtwophase to LOGICALREP_TWOPHASE_STATE_PENDING once.
 					 * After the subscription is enabled, a new logical
 					 * replication worker requests to change the two_phase
 					 * option of its slot from pending to true when the
-					 * initial data synchronization is done. The code path is
-					 * the same as the case in which two_phase is initially
-					 * set to true.
+					 * initial data synchronization is done. That code path is
+					 * the same as when two_phase is initially set to true.
 					 */
 					update_two_phase = !opts.twophase;
 
diff --git a/src/test/subscription/t/021_twophase.pl b/src/test/subscription/t/021_twophase.pl
index c8fb3b7..91e2e17 100644
--- a/src/test/subscription/t/021_twophase.pl
+++ b/src/test/subscription/t/021_twophase.pl
@@ -428,9 +428,8 @@ is($result, qq(0), 'should be no prepared transactions on subscriber');
 
 ###############################
 # Toggle the two_phase to "true" before the COMMIT PREPARED.
-#
-# Since we are the special path for the case where both two_phase
-# and failover are altered, it is also set to "true".
+# Also, set failover to "true" to test the code path where
+# both two_phase and failover are altered at the same time.
 ###############################
 $node_subscriber->safe_psql('postgres',
     "ALTER SUBSCRIPTION tap_sub_copy DISABLE;");

diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index 58db97f..e0ce83a 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -256,10 +256,15 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
      </para>
 
      <para>
-      The <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>
-      parameter can only be altered when the subscription is disabled.
-      When altering the parameter from <literal>true</literal>
-      to <literal>false</literal>, the backend process checks for any incomplete
+      The <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>
+      and <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>
+      parameters can only be altered when the subscription is disabled.
+     </para>
+
+     <para>
+      When altering <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>
+      from <literal>true</literal> to <literal>false</literal>,
+      the backend process checks for any incomplete
       prepared transactions done by the logical replication worker (from when
       <literal>two_phase</literal> parameter was still <literal>true</literal>)
       and, if any are found, an error is reported. If this happens, you can

From 316c24a6933b9e4b82d17e9b60c27fa442b13b31 Mon Sep 17 00:00:00 2001
From: Ajin Cherian <ajinc@fast.au.fujitsu.com>
Date: Fri, 5 Apr 2024 06:47:18 -0400
Subject: [PATCH v20 1/3] Allow altering of two_phase option of a SUBSCRIPTION

This patch allows the user to alter the 'two_phase' option of a subscriber provided no
uncommitted prepared transactions are pending on that subscription.

Author: Cherian Ajin, Hayato Kuroda
---
 doc/src/sgml/protocol.sgml                    |  48 ++++---
 doc/src/sgml/ref/alter_subscription.sgml      |  12 +-
 src/backend/access/transam/twophase.c         |  79 ++++++++++
 src/backend/commands/subscriptioncmds.c       | 135 +++++++++++++-----
 .../libpqwalreceiver/libpqwalreceiver.c       |   9 +-
 src/backend/replication/logical/launcher.c    |  10 +-
 src/backend/replication/logical/worker.c      |  25 +---
 src/backend/replication/slot.c                |  44 ++++--
 src/backend/replication/walsender.c           |  32 +++--
 src/bin/psql/tab-complete.c                   |   2 +-
 src/include/access/twophase.h                 |   5 +
 src/include/replication/slot.h                |   3 +-
 src/include/replication/walreceiver.h         |  11 +-
 src/include/replication/worker_internal.h     |   3 +-
 src/test/regress/expected/subscription.out    |   5 +-
 src/test/regress/sql/subscription.sql         |   5 +-
 src/test/subscription/t/021_twophase.pl       |  86 ++++++++++-
 17 files changed, 383 insertions(+), 131 deletions(-)

diff --git a/doc/src/sgml/protocol.sgml b/doc/src/sgml/protocol.sgml
index 1b27d0a547..24c57fbd89 100644
--- a/doc/src/sgml/protocol.sgml
+++ b/doc/src/sgml/protocol.sgml
@@ -2049,21 +2049,6 @@ psql "dbname=postgres replication=database" -c "IDENTIFY_SYSTEM;"
       <para>The following options are supported:</para>
 
       <variablelist>
-       <varlistentry>
-        <term><literal>TWO_PHASE [ <replaceable class="parameter">boolean</replaceable> ]</literal></term>
-        <listitem>
-         <para>
-          If true, this logical replication slot supports decoding of two-phase
-          commit. With this option, commands related to two-phase commit such as
-          <literal>PREPARE TRANSACTION</literal>, <literal>COMMIT PREPARED</literal>
-          and <literal>ROLLBACK PREPARED</literal> are decoded and transmitted.
-          The transaction will be decoded and transmitted at
-          <literal>PREPARE TRANSACTION</literal> time.
-          The default is false.
-         </para>
-        </listitem>
-       </varlistentry>
-
        <varlistentry>
         <term><literal>RESERVE_WAL [ <replaceable class="parameter">boolean</replaceable> ]</literal></term>
         <listitem>
@@ -2104,6 +2089,21 @@ psql "dbname=postgres replication=database" -c "IDENTIFY_SYSTEM;"
          </para>
         </listitem>
        </varlistentry>
+
+       <varlistentry>
+        <term><literal>TWO_PHASE [ <replaceable class="parameter">boolean</replaceable> ]</literal></term>
+        <listitem>
+         <para>
+          If true, this logical replication slot supports decoding of two-phase
+          commit. With this option, commands related to two-phase commit such as
+          <literal>PREPARE TRANSACTION</literal>, <literal>COMMIT PREPARED</literal>
+          and <literal>ROLLBACK PREPARED</literal> are decoded and transmitted.
+          The transaction will be decoded and transmitted at
+          <literal>PREPARE TRANSACTION</literal> time.
+          The default is false.
+         </para>
+        </listitem>
+       </varlistentry>
       </variablelist>
 
       <para>
@@ -2192,7 +2192,7 @@ psql "dbname=postgres replication=database" -c "IDENTIFY_SYSTEM;"
        </varlistentry>
       </variablelist>
 
-      <para>The following option is supported:</para>
+      <para>The following options are supported:</para>
 
       <variablelist>
        <varlistentry>
@@ -2206,6 +2206,22 @@ psql "dbname=postgres replication=database" -c "IDENTIFY_SYSTEM;"
        </varlistentry>
       </variablelist>
 
+      <variablelist>
+       <varlistentry>
+        <term><literal>TWO_PHASE [ <replaceable class="parameter">boolean</replaceable> ]</literal></term>
+        <listitem>
+         <para>
+          If true, this logical replication slot supports decoding of two-phase
+          commit. With this option, commands related to two-phase commit such as
+          <literal>PREPARE TRANSACTION</literal>, <literal>COMMIT PREPARED</literal>
+          and <literal>ROLLBACK PREPARED</literal> are decoded and transmitted.
+          The transaction will be decoded and transmitted at
+          <literal>PREPARE TRANSACTION</literal> time.
+         </para>
+        </listitem>
+       </varlistentry>
+      </variablelist>
+
      </listitem>
     </varlistentry>
 
diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index 476f195622..0b23df1b77 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -68,8 +68,9 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
   <para>
    Commands <command>ALTER SUBSCRIPTION ... REFRESH PUBLICATION</command>,
    <command>ALTER SUBSCRIPTION ... {SET|ADD|DROP} PUBLICATION ...</command>
-   with <literal>refresh</literal> option as <literal>true</literal> and
-   <command>ALTER SUBSCRIPTION ... SET (failover = true|false)</command>
+   with <literal>refresh</literal> option as <literal>true</literal>,
+   <command>ALTER SUBSCRIPTION ... SET (failover = true|false)</command> and
+   <command>ALTER SUBSCRIPTION ... SET (two_phase = true|false)</command>
    cannot be executed inside a transaction block.
 
    These commands also cannot be executed when the subscription has
@@ -228,9 +229,12 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-disable-on-error"><literal>disable_on_error</literal></link>,
       <link linkend="sql-createsubscription-params-with-password-required"><literal>password_required</literal></link>,
       <link linkend="sql-createsubscription-params-with-run-as-owner"><literal>run_as_owner</literal></link>,
-      <link linkend="sql-createsubscription-params-with-origin"><literal>origin</literal></link>, and
-      <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>.
+      <link linkend="sql-createsubscription-params-with-origin"><literal>origin</literal></link>,
+      <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>, and
+      <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>.
       Only a superuser can set <literal>password_required = false</literal>.
+      The <literal>two_phase</literal> parameter can only be altered when the
+      subscription is disabled.
      </para>
 
      <para>
diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index 9a8257fcaf..d43828d0ea 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -2681,3 +2681,82 @@ LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 	LWLockRelease(TwoPhaseStateLock);
 	return found;
 }
+
+/*
+ * TwoPhaseTransactionGid
+ *		Form the prepared transaction GID for two_phase transactions.
+ *
+ * Return the GID in the supplied buffer.
+ */
+void
+TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid_res, int szgid)
+{
+	Assert(subid != InvalidRepOriginId);
+
+	if (!TransactionIdIsValid(xid))
+		ereport(ERROR,
+				(errcode(ERRCODE_PROTOCOL_VIOLATION),
+				 errmsg_internal("invalid two-phase transaction ID")));
+
+	snprintf(gid_res, szgid, "pg_gid_%u_%u", subid, xid);
+}
+
+/*
+ * IsTwoPhaseTransactionGidForSubid
+ *		Check whether the given GID (as formed by TwoPhaseTransactionGid) is
+ *		for the specified 'subid'.
+ */
+static bool
+IsTwoPhaseTransactionGidForSubid(Oid subid, char *gid)
+{
+	int			ret;
+	Oid			subid_from_gid;
+	TransactionId xid_from_gid;
+	char		gid_generated[GIDSIZE];
+
+	/* Extract the subid and xid from the given GID */
+	ret = sscanf(gid, "pg_gid_%u_%u", &subid_from_gid, &xid_from_gid);
+
+	/*
+	 * Check that the given GID has expected format, and at least the subid
+	 * matches.
+	 */
+	if (ret != 2 || subid != subid_from_gid)
+		return false;
+
+	/*
+	 * Reconstruct a tmp GID based on the subid and xid extracted from the
+	 * given GID. Check that the tmp GID and the given GID match.
+	 */
+	TwoPhaseTransactionGid(subid, xid_from_gid, gid_generated,
+						   sizeof(gid_generated));
+
+	return strcmp(gid, gid_generated) == 0;
+}
+
+/*
+ * LookupGXactBySubid
+ *		Check if the prepared transaction done by apply worker exists.
+ */
+bool
+LookupGXactBySubid(Oid subid)
+{
+	bool		found = false;
+
+	LWLockAcquire(TwoPhaseStateLock, LW_SHARED);
+	for (int i = 0; i < TwoPhaseState->numPrepXacts; i++)
+	{
+		GlobalTransaction gxact = TwoPhaseState->prepXacts[i];
+
+		/* Ignore not-yet-valid GIDs. */
+		if (gxact->valid &&
+			IsTwoPhaseTransactionGidForSubid(subid, gxact->gid))
+		{
+			found = true;
+			break;
+		}
+	}
+	LWLockRelease(TwoPhaseStateLock);
+
+	return found;
+}
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index 16d83b3253..4f6ad3f7ba 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -16,6 +16,7 @@
 
 #include "access/htup_details.h"
 #include "access/table.h"
+#include "access/twophase.h"
 #include "access/xact.h"
 #include "catalog/catalog.h"
 #include "catalog/dependency.h"
@@ -109,6 +110,8 @@ static void check_publications_origin(WalReceiverConn *wrconn,
 static void check_duplicates_in_publist(List *publist, Datum *datums);
 static List *merge_publications(List *oldpublist, List *newpublist, bool addpub, const char *subname);
 static void ReportSlotConnectionError(List *rstates, Oid subid, char *slotname, char *err);
+static void CheckAlterSubOption(Subscription *sub, const char *option,
+								bool isTopLevel);
 
 
 /*
@@ -259,21 +262,9 @@ parse_subscription_options(ParseState *pstate, List *stmt_options,
 			opts->specified_opts |= SUBOPT_STREAMING;
 			opts->streaming = defGetStreamingMode(defel);
 		}
-		else if (strcmp(defel->defname, "two_phase") == 0)
+		else if (IsSet(supported_opts, SUBOPT_TWOPHASE_COMMIT) &&
+				 strcmp(defel->defname, "two_phase") == 0)
 		{
-			/*
-			 * Do not allow toggling of two_phase option. Doing so could cause
-			 * missing of transactions and lead to an inconsistent replica.
-			 * See comments atop worker.c
-			 *
-			 * Note: Unsupported twophase indicates that this call originated
-			 * from AlterSubscription.
-			 */
-			if (!IsSet(supported_opts, SUBOPT_TWOPHASE_COMMIT))
-				ereport(ERROR,
-						(errcode(ERRCODE_SYNTAX_ERROR),
-						 errmsg("unrecognized subscription parameter: \"%s\"", defel->defname)));
-
 			if (IsSet(opts->specified_opts, SUBOPT_TWOPHASE_COMMIT))
 				errorConflictingDefElem(defel, pstate);
 
@@ -1079,6 +1070,47 @@ AlterSubscription_refresh(Subscription *sub, bool copy_data,
 		table_close(rel, NoLock);
 }
 
+/*
+ * Common checks for altering failover and two_phase option
+ */
+static void
+CheckAlterSubOption(Subscription *sub, const char *option, bool isTopLevel)
+{
+	StringInfoData cmd;
+
+	Assert(strcmp(option, "failover") == 0 ||
+		   strcmp(option, "two_phase") == 0);
+
+	if (!sub->slotname)
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("cannot set %s for a subscription that does not have a slot name",
+						option)));
+
+	/*
+	 * Do not allow changing the option if the subscription is enabled. This
+	 * is because both failover and two_phase options of the slot on the
+	 * publisher cannot be modified if the slot is currently acquired by the
+	 * apply worker.
+	 */
+	if (sub->enabled)
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("cannot set %s for enabled subscription",
+						option)));
+
+	initStringInfo(&cmd);
+	appendStringInfo(&cmd, "ALTER SUBSCRIPTION ... SET (%s)", option);
+
+	/*
+	 * The changed option of the slot can't be rolled back, so disallow if we
+	 * are in a transaction block.
+	 */
+	PreventInTransactionBlock(isTopLevel, cmd.data);
+
+	pfree(cmd.data);
+}
+
 /*
  * Alter the existing subscription.
  */
@@ -1145,7 +1177,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 			{
 				supported_opts = (SUBOPT_SLOT_NAME |
 								  SUBOPT_SYNCHRONOUS_COMMIT | SUBOPT_BINARY |
-								  SUBOPT_STREAMING | SUBOPT_DISABLE_ON_ERR |
+								  SUBOPT_STREAMING | SUBOPT_TWOPHASE_COMMIT |
+								  SUBOPT_DISABLE_ON_ERR |
 								  SUBOPT_PASSWORD_REQUIRED |
 								  SUBOPT_RUN_AS_OWNER | SUBOPT_FAILOVER |
 								  SUBOPT_ORIGIN);
@@ -1229,33 +1262,60 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 
 				if (IsSet(opts.specified_opts, SUBOPT_FAILOVER))
 				{
-					if (!sub->slotname)
+					CheckAlterSubOption(sub, "failover", isTopLevel);
+
+					values[Anum_pg_subscription_subfailover - 1] =
+						BoolGetDatum(opts.failover);
+					replaces[Anum_pg_subscription_subfailover - 1] = true;
+				}
+
+				if (IsSet(opts.specified_opts, SUBOPT_TWOPHASE_COMMIT))
+				{
+					CheckAlterSubOption(sub, "two_phase", isTopLevel);
+
+					/*
+					 * Modifying the two_phase slot option requires a slot
+					 * lookup by slot name, so changing the slot name at the
+					 * same time is not allowed.
+					 */
+					if (IsSet(opts.specified_opts, SUBOPT_SLOT_NAME))
 						ereport(ERROR,
-								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-								 errmsg("cannot set %s for a subscription that does not have a slot name",
-										"failover")));
+								(errcode(ERRCODE_SYNTAX_ERROR),
+								 errmsg("slot_name and two_phase cannot be altered at the same time")));
 
 					/*
-					 * Do not allow changing the failover state if the
-					 * subscription is enabled. This is because the failover
-					 * state of the slot on the publisher cannot be modified
-					 * if the slot is currently acquired by the apply worker.
+					 * Workers may still survive even if the subscription has
+					 * been disabled. They may read the pg_subscription
+					 * catalog and detect that the two_phase parameter is
+					 * updated, which causes an assertion failure that
+					 * two_phase should not be updated while the worker
+					 * exists. Ensure workers have already been exited to
+					 * avoid it.
 					 */
-					if (sub->enabled)
+					if (logicalrep_workers_find(subid, true, true))
 						ereport(ERROR,
 								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-								 errmsg("cannot set %s for enabled subscription",
-										"failover")));
+								 errmsg("cannot alter two_phase when logical replication worker is still running"),
+								 errhint("Wait certain time and try again.")));
 
 					/*
-					 * The changed failover option of the slot can't be rolled
-					 * back.
+					 * two_phase cannot be disabled if there are any
+					 * uncommitted prepared transactions present.
 					 */
-					PreventInTransactionBlock(isTopLevel, "ALTER SUBSCRIPTION ... SET (failover)");
-
-					values[Anum_pg_subscription_subfailover - 1] =
-						BoolGetDatum(opts.failover);
-					replaces[Anum_pg_subscription_subfailover - 1] = true;
+					if (!opts.twophase &&
+						sub->twophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
+						LookupGXactBySubid(subid))
+						ereport(ERROR,
+								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+								 errmsg("cannot disable two_phase when prepared transactions are present"),
+								 errhint("Resolve these transactions and try again.")));
+
+					/* Change system catalog accordingly */
+					values[Anum_pg_subscription_subtwophasestate - 1] =
+						CharGetDatum(opts.twophase ?
+									 LOGICALREP_TWOPHASE_STATE_PENDING :
+									 LOGICALREP_TWOPHASE_STATE_DISABLED);
+					replaces[Anum_pg_subscription_subtwophasestate - 1] = true;
 				}
 
 				if (IsSet(opts.specified_opts, SUBOPT_ORIGIN))
@@ -1507,7 +1567,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 	 * doing the database operations we won't be able to rollback altered
 	 * slot.
 	 */
-	if (replaces[Anum_pg_subscription_subfailover - 1])
+	if (replaces[Anum_pg_subscription_subfailover - 1] ||
+		replaces[Anum_pg_subscription_subtwophasestate - 1])
 	{
 		bool		must_use_password;
 		char	   *err;
@@ -1528,7 +1589,7 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 
 		PG_TRY();
 		{
-			walrcv_alter_slot(wrconn, sub->slotname, opts.failover);
+			walrcv_alter_slot(wrconn, sub->slotname, opts.failover, opts.twophase);
 		}
 		PG_FINALLY();
 		{
@@ -1675,9 +1736,7 @@ DropSubscription(DropSubscriptionStmt *stmt, bool isTopLevel)
 	 * New workers won't be started because we hold an exclusive lock on the
 	 * subscription till the end of the transaction.
 	 */
-	LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
-	subworkers = logicalrep_workers_find(subid, false);
-	LWLockRelease(LogicalRepWorkerLock);
+	subworkers = logicalrep_workers_find(subid, false, true);
 	foreach(lc, subworkers)
 	{
 		LogicalRepWorker *w = (LogicalRepWorker *) lfirst(lc);
diff --git a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
index 6c42c209d2..1cb601a148 100644
--- a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
+++ b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
@@ -80,7 +80,7 @@ static char *libpqrcv_create_slot(WalReceiverConn *conn,
 								  CRSSnapshotAction snapshot_action,
 								  XLogRecPtr *lsn);
 static void libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-								bool failover);
+								bool failover, bool two_phase);
 static pid_t libpqrcv_get_backend_pid(WalReceiverConn *conn);
 static WalRcvExecResult *libpqrcv_exec(WalReceiverConn *conn,
 									   const char *query,
@@ -1121,15 +1121,16 @@ libpqrcv_create_slot(WalReceiverConn *conn, const char *slotname,
  */
 static void
 libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-					bool failover)
+					bool failover, bool two_phase)
 {
 	StringInfoData cmd;
 	PGresult   *res;
 
 	initStringInfo(&cmd);
-	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( FAILOVER %s )",
+	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( FAILOVER %s, TWO_PHASE %s )",
 					 quote_identifier(slotname),
-					 failover ? "true" : "false");
+					 failover ? "true" : "false",
+					 two_phase ? "true" : "false");
 
 	res = libpqrcv_PQexec(conn->streamConn, cmd.data);
 	pfree(cmd.data);
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 27c3a91fb7..c566d50a07 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -272,11 +272,14 @@ logicalrep_worker_find(Oid subid, Oid relid, bool only_running)
  * the subscription, instead of just one.
  */
 List *
-logicalrep_workers_find(Oid subid, bool only_running)
+logicalrep_workers_find(Oid subid, bool only_running, bool acquire_lock)
 {
 	int			i;
 	List	   *res = NIL;
 
+	if (acquire_lock)
+		LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
+
 	Assert(LWLockHeldByMe(LogicalRepWorkerLock));
 
 	/* Search for attached worker for a given subscription id. */
@@ -288,6 +291,9 @@ logicalrep_workers_find(Oid subid, bool only_running)
 			res = lappend(res, w);
 	}
 
+	if (acquire_lock)
+		LWLockRelease(LogicalRepWorkerLock);
+
 	return res;
 }
 
@@ -759,7 +765,7 @@ logicalrep_worker_detach(void)
 
 		LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
 
-		workers = logicalrep_workers_find(MyLogicalRepWorker->subid, true);
+		workers = logicalrep_workers_find(MyLogicalRepWorker->subid, true, false);
 		foreach(lc, workers)
 		{
 			LogicalRepWorker *w = (LogicalRepWorker *) lfirst(lc);
diff --git a/src/backend/replication/logical/worker.c b/src/backend/replication/logical/worker.c
index c0bda6269b..6c798cd5b4 100644
--- a/src/backend/replication/logical/worker.c
+++ b/src/backend/replication/logical/worker.c
@@ -401,9 +401,6 @@ static void apply_handle_tuple_routing(ApplyExecutionData *edata,
 									   LogicalRepTupleData *newtup,
 									   CmdType operation);
 
-/* Compute GID for two_phase transactions */
-static void TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid, int szgid);
-
 /* Functions for skipping changes */
 static void maybe_start_skipping_changes(XLogRecPtr finish_lsn);
 static void stop_skipping_changes(void);
@@ -3911,7 +3908,7 @@ maybe_reread_subscription(void)
 	/* !slotname should never happen when enabled is true. */
 	Assert(newsub->slotname);
 
-	/* two-phase should not be altered */
+	/* two-phase cannot be altered while the worker exists */
 	Assert(newsub->twophasestate == MySubscription->twophasestate);
 
 	/*
@@ -4396,24 +4393,6 @@ cleanup_subxact_info()
 	subxact_data.nsubxacts_max = 0;
 }
 
-/*
- * Form the prepared transaction GID for two_phase transactions.
- *
- * Return the GID in the supplied buffer.
- */
-static void
-TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid, int szgid)
-{
-	Assert(subid != InvalidRepOriginId);
-
-	if (!TransactionIdIsValid(xid))
-		ereport(ERROR,
-				(errcode(ERRCODE_PROTOCOL_VIOLATION),
-				 errmsg_internal("invalid two-phase transaction ID")));
-
-	snprintf(gid, szgid, "pg_gid_%u_%u", subid, xid);
-}
-
 /*
  * Common function to run the apply loop with error handling. Disable the
  * subscription, if necessary.
@@ -5014,7 +4993,7 @@ AtEOXact_LogicalRepWorkers(bool isCommit)
 			List	   *workers;
 			ListCell   *lc2;
 
-			workers = logicalrep_workers_find(subid, true);
+			workers = logicalrep_workers_find(subid, true, false);
 			foreach(lc2, workers)
 			{
 				LogicalRepWorker *worker = (LogicalRepWorker *) lfirst(lc2);
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index baf9b89dc4..90494cb858 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -804,9 +804,12 @@ ReplicationSlotDrop(const char *name, bool nowait)
  * Change the definition of the slot identified by the specified name.
  */
 void
-ReplicationSlotAlter(const char *name, bool failover)
+ReplicationSlotAlter(const char *name, bool *failover, bool *two_phase)
 {
+	bool		update_slot = false;
+
 	Assert(MyReplicationSlot == NULL);
+	Assert(failover || two_phase);
 
 	ReplicationSlotAcquire(name, false);
 
@@ -832,28 +835,45 @@ ReplicationSlotAlter(const char *name, bool failover)
 		 * Do not allow users to enable failover on the standby as we do not
 		 * support sync to the cascading standby.
 		 */
-		if (failover)
+		if (failover && *failover)
 			ereport(ERROR,
 					errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 					errmsg("cannot enable failover for a replication slot"
 						   " on the standby"));
 	}
 
-	/*
-	 * Do not allow users to enable failover for temporary slots as we do not
-	 * support syncing temporary slots to the standby.
-	 */
-	if (failover && MyReplicationSlot->data.persistency == RS_TEMPORARY)
-		ereport(ERROR,
-				errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-				errmsg("cannot enable failover for a temporary replication slot"));
+	if (failover)
+	{
+		/*
+		 * Do not allow users to enable failover for temporary slots as we do
+		 * not support syncing temporary slots to the standby.
+		 */
+		if (*failover && MyReplicationSlot->data.persistency == RS_TEMPORARY)
+			ereport(ERROR,
+					errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+					errmsg("cannot enable failover for a temporary replication slot"));
+
+		if (MyReplicationSlot->data.failover != *failover)
+		{
+			SpinLockAcquire(&MyReplicationSlot->mutex);
+			MyReplicationSlot->data.failover = *failover;
+			SpinLockRelease(&MyReplicationSlot->mutex);
+
+			update_slot = true;
+		}
+	}
 
-	if (MyReplicationSlot->data.failover != failover)
+	if (two_phase && MyReplicationSlot->data.two_phase != *two_phase)
 	{
 		SpinLockAcquire(&MyReplicationSlot->mutex);
-		MyReplicationSlot->data.failover = failover;
+		MyReplicationSlot->data.two_phase = *two_phase;
 		SpinLockRelease(&MyReplicationSlot->mutex);
 
+		update_slot = true;
+	}
+
+	if (update_slot)
+	{
 		ReplicationSlotMarkDirty();
 		ReplicationSlotSave();
 	}
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index ca205594bd..c5f1009f37 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1407,12 +1407,15 @@ DropReplicationSlot(DropReplicationSlotCmd *cmd)
 }
 
 /*
- * Process extra options given to ALTER_REPLICATION_SLOT.
+ * Change the definition of a replication slot.
  */
 static void
-ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd, bool *failover)
+AlterReplicationSlot(AlterReplicationSlotCmd *cmd)
 {
 	bool		failover_given = false;
+	bool		two_phase_given = false;
+	bool		failover;
+	bool		two_phase;
 
 	/* Parse options */
 	foreach_ptr(DefElem, defel, cmd->options)
@@ -1424,23 +1427,24 @@ ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd, bool *failover)
 						(errcode(ERRCODE_SYNTAX_ERROR),
 						 errmsg("conflicting or redundant options")));
 			failover_given = true;
-			*failover = defGetBoolean(defel);
+			failover = defGetBoolean(defel);
+		}
+		else if (strcmp(defel->defname, "two_phase") == 0)
+		{
+			if (two_phase_given)
+				ereport(ERROR,
+						(errcode(ERRCODE_SYNTAX_ERROR),
+						 errmsg("conflicting or redundant options")));
+			two_phase_given = true;
+			two_phase = defGetBoolean(defel);
 		}
 		else
 			elog(ERROR, "unrecognized option: %s", defel->defname);
 	}
-}
-
-/*
- * Change the definition of a replication slot.
- */
-static void
-AlterReplicationSlot(AlterReplicationSlotCmd *cmd)
-{
-	bool		failover = false;
 
-	ParseAlterReplSlotOptions(cmd, &failover);
-	ReplicationSlotAlter(cmd->slotname, failover);
+	ReplicationSlotAlter(cmd->slotname,
+						 failover_given ? &failover : NULL,
+						 two_phase_given ? &two_phase : NULL);
 }
 
 /*
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
index d453e224d9..891face1b6 100644
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -1948,7 +1948,7 @@ psql_completion(const char *text, int start, int end)
 	else if (HeadMatches("ALTER", "SUBSCRIPTION", MatchAny) && TailMatches("SET", "("))
 		COMPLETE_WITH("binary", "disable_on_error", "failover", "origin",
 					  "password_required", "run_as_owner", "slot_name",
-					  "streaming", "synchronous_commit");
+					  "streaming", "synchronous_commit", "two_phase");
 	/* ALTER SUBSCRIPTION <name> SKIP ( */
 	else if (HeadMatches("ALTER", "SUBSCRIPTION", MatchAny) && TailMatches("SKIP", "("))
 		COMPLETE_WITH("lsn");
diff --git a/src/include/access/twophase.h b/src/include/access/twophase.h
index 56248c0006..b85b65c604 100644
--- a/src/include/access/twophase.h
+++ b/src/include/access/twophase.h
@@ -62,4 +62,9 @@ extern void PrepareRedoRemove(TransactionId xid, bool giveWarning);
 extern void restoreTwoPhaseData(void);
 extern bool LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 						TimestampTz origin_prepare_timestamp);
+
+extern void TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid_res,
+								   int szgid);
+extern bool LookupGXactBySubid(Oid subid);
+
 #endif							/* TWOPHASE_H */
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index c9675ee87c..cde164472a 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -243,7 +243,8 @@ extern void ReplicationSlotCreate(const char *name, bool db_specific,
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
 extern void ReplicationSlotDropAcquired(void);
-extern void ReplicationSlotAlter(const char *name, bool failover);
+extern void ReplicationSlotAlter(const char *name, bool *failover,
+								 bool *two_phase);
 
 extern void ReplicationSlotAcquire(const char *name, bool nowait);
 extern void ReplicationSlotRelease(void);
diff --git a/src/include/replication/walreceiver.h b/src/include/replication/walreceiver.h
index 12f71fa99b..31fa1257ec 100644
--- a/src/include/replication/walreceiver.h
+++ b/src/include/replication/walreceiver.h
@@ -372,12 +372,13 @@ typedef char *(*walrcv_create_slot_fn) (WalReceiverConn *conn,
 /*
  * walrcv_alter_slot_fn
  *
- * Change the definition of a replication slot. Currently, it only supports
- * changing the failover property of the slot.
+ * Change the definition of a replication slot. Currently, it supports
+ * changing the failover and the two_phase property of the slot.
  */
 typedef void (*walrcv_alter_slot_fn) (WalReceiverConn *conn,
 									  const char *slotname,
-									  bool failover);
+									  bool failover,
+									  bool two_phase);
 
 /*
  * walrcv_get_backend_pid_fn
@@ -455,8 +456,8 @@ extern PGDLLIMPORT WalReceiverFunctionsType *WalReceiverFunctions;
 	WalReceiverFunctions->walrcv_send(conn, buffer, nbytes)
 #define walrcv_create_slot(conn, slotname, temporary, two_phase, failover, snapshot_action, lsn) \
 	WalReceiverFunctions->walrcv_create_slot(conn, slotname, temporary, two_phase, failover, snapshot_action, lsn)
-#define walrcv_alter_slot(conn, slotname, failover) \
-	WalReceiverFunctions->walrcv_alter_slot(conn, slotname, failover)
+#define walrcv_alter_slot(conn, slotname, failover, two_phase) \
+	WalReceiverFunctions->walrcv_alter_slot(conn, slotname, failover, two_phase)
 #define walrcv_get_backend_pid(conn) \
 	WalReceiverFunctions->walrcv_get_backend_pid(conn)
 #define walrcv_exec(conn, exec, nRetTypes, retTypes) \
diff --git a/src/include/replication/worker_internal.h b/src/include/replication/worker_internal.h
index 515aefd519..9646261d7e 100644
--- a/src/include/replication/worker_internal.h
+++ b/src/include/replication/worker_internal.h
@@ -240,7 +240,8 @@ extern PGDLLIMPORT bool InitializingApplyWorker;
 extern void logicalrep_worker_attach(int slot);
 extern LogicalRepWorker *logicalrep_worker_find(Oid subid, Oid relid,
 												bool only_running);
-extern List *logicalrep_workers_find(Oid subid, bool only_running);
+extern List *logicalrep_workers_find(Oid subid, bool only_running,
+									 bool acquire_lock);
 extern bool logicalrep_worker_launch(LogicalRepWorkerType wtype,
 									 Oid dbid, Oid subid, const char *subname,
 									 Oid userid, Oid relid,
diff --git a/src/test/regress/expected/subscription.out b/src/test/regress/expected/subscription.out
index 5c2f1ee517..17d48b1685 100644
--- a/src/test/regress/expected/subscription.out
+++ b/src/test/regress/expected/subscription.out
@@ -377,10 +377,7 @@ HINT:  To initiate replication, you must manually create the replication slot, e
  regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | p                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
---fail - alter of two_phase option not supported.
-ALTER SUBSCRIPTION regress_testsub SET (two_phase = false);
-ERROR:  unrecognized subscription parameter: "two_phase"
--- but can alter streaming when two_phase enabled
+-- we can alter streaming when two_phase enabled
 ALTER SUBSCRIPTION regress_testsub SET (streaming = true);
 \dRs+
                                                                                                                 List of subscriptions
diff --git a/src/test/regress/sql/subscription.sql b/src/test/regress/sql/subscription.sql
index 3e5ba4cb8c..007c9e7037 100644
--- a/src/test/regress/sql/subscription.sql
+++ b/src/test/regress/sql/subscription.sql
@@ -256,10 +256,7 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUBLICATION testpub WITH (connect = false, two_phase = true);
 
 \dRs+
---fail - alter of two_phase option not supported.
-ALTER SUBSCRIPTION regress_testsub SET (two_phase = false);
-
--- but can alter streaming when two_phase enabled
+-- we can alter streaming when two_phase enabled
 ALTER SUBSCRIPTION regress_testsub SET (streaming = true);
 
 \dRs+
diff --git a/src/test/subscription/t/021_twophase.pl b/src/test/subscription/t/021_twophase.pl
index 9437cd4c3b..da40fcd614 100644
--- a/src/test/subscription/t/021_twophase.pl
+++ b/src/test/subscription/t/021_twophase.pl
@@ -367,6 +367,90 @@ $result =
   $node_subscriber->safe_psql('postgres', "SELECT count(*) FROM tab_copy;");
 is($result, qq(2), 'replicated data in subscriber table');
 
+# Clean up
+$node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub");
+
+###############################
+# Alter the subscription to two_phase = false.
+# Verify that the altered subscription reflects the two_phase option.
+###############################
+
+# Alter subscription two_phase to false
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy DISABLE;");
+$node_subscriber->poll_query_until('postgres',
+	"SELECT count(*) = 0 FROM pg_stat_activity WHERE backend_type = 'logical replication worker'"
+);
+$node_subscriber->safe_psql(
+	'postgres', "
+    ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = false);
+    ALTER SUBSCRIPTION tap_sub_copy ENABLE;");
+
+# Wait for subscription startup
+$node_subscriber->wait_for_subscription_sync($node_publisher, $appname_copy);
+
+# Make sure that the two-phase is disabled on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT subtwophasestate FROM pg_subscription WHERE subname = 'tap_sub_copy';"
+);
+is($result, qq(d), 'two-phase should be disabled');
+
+###############################
+# Now do a prepare on the publisher.
+# Verify that it is not replicated.
+###############################
+$node_publisher->safe_psql(
+	'postgres', qq{
+    BEGIN;
+    INSERT INTO tab_copy VALUES (100);
+    PREPARE TRANSACTION 'newgid';
+	});
+
+# Wait for the subscriber to catchup
+$node_publisher->wait_for_catchup($appname_copy);
+
+# Make sure there are no prepared transactions on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT count(*) FROM pg_prepared_xacts;");
+is($result, qq(0), 'should be no prepared transactions on subscriber');
+
+###############################
+# Now commit the insert.
+# Verify that it is replicated.
+###############################
+$node_publisher->safe_psql('postgres', "COMMIT PREPARED 'newgid';");
+
+# Wait for the subscriber to catchup
+$node_publisher->wait_for_catchup($appname_copy);
+
+# Make sure that the committed transaction is replicated.
+$result =
+  $node_subscriber->safe_psql('postgres', "SELECT count(*) FROM tab_copy;");
+is($result, qq(3), 'replicated data in subscriber table');
+
+###############################
+# Alter the subscription to two_phase = true.
+# Verify that the altered subscription reflects the two_phase option.
+###############################
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy DISABLE;");
+$node_subscriber->poll_query_until('postgres',
+	"SELECT count(*) = 0 FROM pg_stat_activity WHERE backend_type = 'logical replication worker'"
+);
+$node_subscriber->safe_psql(
+	'postgres', "
+    ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = true);
+    ALTER SUBSCRIPTION tap_sub_copy ENABLE;");
+
+# Wait for subscription startup
+$node_subscriber->wait_for_subscription_sync($node_publisher, $appname_copy);
+
+# Make sure that the two-phase is enabled on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT subtwophasestate FROM pg_subscription WHERE subname = 'tap_sub_copy';"
+);
+is($result, qq(e), 'two-phase should be enabled');
+
 $node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub_copy;");
 $node_publisher->safe_psql('postgres', "DROP PUBLICATION tap_pub_copy;");
 
@@ -374,8 +458,6 @@ $node_publisher->safe_psql('postgres', "DROP PUBLICATION tap_pub_copy;");
 # check all the cleanup
 ###############################
 
-$node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub");
-
 $result = $node_subscriber->safe_psql('postgres',
 	"SELECT count(*) FROM pg_subscription");
 is($result, qq(0), 'check subscription was dropped on subscriber');
-- 
2.43.0

From 50aab8d8d47b90268e0034ddadb7284ef8b15ffe Mon Sep 17 00:00:00 2001
From: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Date: Wed, 17 Apr 2024 06:18:23 +0000
Subject: [PATCH v20 2/3] Alter slot option two_phase only when altering "true"
 to "false"

Since the two_phase option is controlled by both the publisher (as a slot option)
and the subscriber (as a subscription option), the slot option must also be
modified.

Regarding the false->true case, the backend process alters the subtwophase to
LOGICALREP_TWOPHASE_STATE_PENDING once. After the subscription is enabled, a new
logical replication worker requests to change the two_phase option of its slot
from pending to true after the initial data synchronization is done. The code
path is the same as the case in which two_phase is initially set to true, so
there is no need to do something remarkable. However, for the true->false case,
the backend must connect to the publisher and expressly change the parameter
because the apply worker does not alter the option to false. Because this
operation cannot be rolled back, altering the two_phase parameter from "true"
to "false" within a transaction is prohibited.
---
 doc/src/sgml/ref/alter_subscription.sgml      |  2 +-
 src/backend/commands/subscriptioncmds.c       | 76 ++++++++++++++-----
 .../libpqwalreceiver/libpqwalreceiver.c       | 23 ++++--
 src/include/replication/walreceiver.h         |  5 +-
 src/test/subscription/t/021_twophase.pl       | 47 +++++++-----
 5 files changed, 108 insertions(+), 45 deletions(-)

diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index 0b23df1b77..df44415661 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -70,7 +70,7 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
    <command>ALTER SUBSCRIPTION ... {SET|ADD|DROP} PUBLICATION ...</command>
    with <literal>refresh</literal> option as <literal>true</literal>,
    <command>ALTER SUBSCRIPTION ... SET (failover = true|false)</command> and
-   <command>ALTER SUBSCRIPTION ... SET (two_phase = true|false)</command>
+   <command>ALTER SUBSCRIPTION ... SET (two_phase = false)</command>
    cannot be executed inside a transaction block.
 
    These commands also cannot be executed when the subscription has
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index 4f6ad3f7ba..0893634abf 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -111,7 +111,7 @@ static void check_duplicates_in_publist(List *publist, Datum *datums);
 static List *merge_publications(List *oldpublist, List *newpublist, bool addpub, const char *subname);
 static void ReportSlotConnectionError(List *rstates, Oid subid, char *slotname, char *err);
 static void CheckAlterSubOption(Subscription *sub, const char *option,
-								bool isTopLevel);
+								bool slot_needs_update, bool isTopLevel);
 
 
 /*
@@ -1074,14 +1074,18 @@ AlterSubscription_refresh(Subscription *sub, bool copy_data,
  * Common checks for altering failover and two_phase option
  */
 static void
-CheckAlterSubOption(Subscription *sub, const char *option, bool isTopLevel)
+CheckAlterSubOption(Subscription *sub, const char *option,
+					bool slot_needs_update, bool isTopLevel)
 {
-	StringInfoData cmd;
-
 	Assert(strcmp(option, "failover") == 0 ||
 		   strcmp(option, "two_phase") == 0);
 
-	if (!sub->slotname)
+	/*
+	 * If the slot needs to be updated, the backend must connect to the
+	 * publisher and request the alteration. slot_name must be required at
+	 * that time.
+	 */
+	if (slot_needs_update && !sub->slotname)
 		ereport(ERROR,
 				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
 				 errmsg("cannot set %s for a subscription that does not have a slot name",
@@ -1099,16 +1103,20 @@ CheckAlterSubOption(Subscription *sub, const char *option, bool isTopLevel)
 				 errmsg("cannot set %s for enabled subscription",
 						option)));
 
-	initStringInfo(&cmd);
-	appendStringInfo(&cmd, "ALTER SUBSCRIPTION ... SET (%s)", option);
-
 	/*
 	 * The changed option of the slot can't be rolled back, so disallow if we
 	 * are in a transaction block.
 	 */
-	PreventInTransactionBlock(isTopLevel, cmd.data);
+	if (slot_needs_update)
+	{
+		StringInfoData cmd;
 
-	pfree(cmd.data);
+		initStringInfo(&cmd);
+		appendStringInfo(&cmd, "ALTER SUBSCRIPTION ... SET (%s)", option);
+
+		PreventInTransactionBlock(isTopLevel, cmd.data);
+		pfree(cmd.data);
+	}
 }
 
 /*
@@ -1126,6 +1134,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 	HeapTuple	tup;
 	Oid			subid;
 	bool		update_tuple = false;
+	bool		update_failover = false;
+	bool		update_two_phase = false;
 	Subscription *sub;
 	Form_pg_subscription form;
 	bits32		supported_opts;
@@ -1262,7 +1272,16 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 
 				if (IsSet(opts.specified_opts, SUBOPT_FAILOVER))
 				{
-					CheckAlterSubOption(sub, "failover", isTopLevel);
+					/*
+					 * First, mark the need to alter the replication slot.
+					 * Failover option is controlled by both the publisher (as
+					 * a slot option) and the subscriber (as a subscription
+					 * option).
+					 */
+					update_failover = true;
+
+					CheckAlterSubOption(sub, "failover", update_failover,
+										isTopLevel);
 
 					values[Anum_pg_subscription_subfailover - 1] =
 						BoolGetDatum(opts.failover);
@@ -1271,14 +1290,34 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 
 				if (IsSet(opts.specified_opts, SUBOPT_TWOPHASE_COMMIT))
 				{
-					CheckAlterSubOption(sub, "two_phase", isTopLevel);
+					/*
+					 * First, check the need to alter the replication slot.
+					 * Two_phase option is controlled by both the publisher
+					 * (as a slot option) and the subscriber (as a
+					 * subscription option). The slot option must be altered
+					 * only when changing "true" to "false".
+					 *
+					 * There is no need to do anything remarkable for the
+					 * "false" to "true" case; the backend process alters
+					 * subtwophase to LOGICALREP_TWOPHASE_STATE_PENDING once.
+					 * After the subscription is enabled, a new logical
+					 * replication worker requests to change the two_phase
+					 * option of its slot from pending to true when the
+					 * initial data synchronization is done. That code path is
+					 * the same as when two_phase is initially set to true.
+					 */
+					update_two_phase = !opts.twophase;
+
+					CheckAlterSubOption(sub, "two_phase", update_two_phase,
+										isTopLevel);
 
 					/*
 					 * Modifying the two_phase slot option requires a slot
 					 * lookup by slot name, so changing the slot name at the
 					 * same time is not allowed.
 					 */
-					if (IsSet(opts.specified_opts, SUBOPT_SLOT_NAME))
+					if (update_two_phase &&
+						IsSet(opts.specified_opts, SUBOPT_SLOT_NAME))
 						ereport(ERROR,
 								(errcode(ERRCODE_SYNTAX_ERROR),
 								 errmsg("slot_name and two_phase cannot be altered at the same time")));
@@ -1302,7 +1341,7 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 					 * two_phase cannot be disabled if there are any
 					 * uncommitted prepared transactions present.
 					 */
-					if (!opts.twophase &&
+					if (update_two_phase &&
 						sub->twophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
 						LookupGXactBySubid(subid))
 						ereport(ERROR,
@@ -1561,14 +1600,13 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 	}
 
 	/*
-	 * Try to acquire the connection necessary for altering slot.
+	 * Try to acquire the connection necessary for altering slot, if needed.
 	 *
 	 * This has to be at the end because otherwise if there is an error while
 	 * doing the database operations we won't be able to rollback altered
 	 * slot.
 	 */
-	if (replaces[Anum_pg_subscription_subfailover - 1] ||
-		replaces[Anum_pg_subscription_subtwophasestate - 1])
+	if (update_failover || update_two_phase)
 	{
 		bool		must_use_password;
 		char	   *err;
@@ -1589,7 +1627,9 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 
 		PG_TRY();
 		{
-			walrcv_alter_slot(wrconn, sub->slotname, opts.failover, opts.twophase);
+			walrcv_alter_slot(wrconn, sub->slotname,
+							  update_failover ? &opts.failover : NULL,
+							  update_two_phase ? &opts.twophase : NULL);
 		}
 		PG_FINALLY();
 		{
diff --git a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
index 1cb601a148..97f957cd87 100644
--- a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
+++ b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
@@ -80,7 +80,7 @@ static char *libpqrcv_create_slot(WalReceiverConn *conn,
 								  CRSSnapshotAction snapshot_action,
 								  XLogRecPtr *lsn);
 static void libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-								bool failover, bool two_phase);
+								const bool *failover, const bool *two_phase);
 static pid_t libpqrcv_get_backend_pid(WalReceiverConn *conn);
 static WalRcvExecResult *libpqrcv_exec(WalReceiverConn *conn,
 									   const char *query,
@@ -1121,16 +1121,27 @@ libpqrcv_create_slot(WalReceiverConn *conn, const char *slotname,
  */
 static void
 libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-					bool failover, bool two_phase)
+					const bool *failover, const bool *two_phase)
 {
 	StringInfoData cmd;
 	PGresult   *res;
 
 	initStringInfo(&cmd);
-	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( FAILOVER %s, TWO_PHASE %s )",
-					 quote_identifier(slotname),
-					 failover ? "true" : "false",
-					 two_phase ? "true" : "false");
+	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( ",
+					 quote_identifier(slotname));
+
+	if (failover)
+		appendStringInfo(&cmd, "FAILOVER %s",
+						 *failover ? "true" : "false");
+
+	if (failover && two_phase)
+		appendStringInfo(&cmd, ", ");
+
+	if (two_phase)
+		appendStringInfo(&cmd, "TWO_PHASE %s",
+						 *two_phase ? "true" : "false");
+
+	appendStringInfoString(&cmd, " );");
 
 	res = libpqrcv_PQexec(conn->streamConn, cmd.data);
 	pfree(cmd.data);
diff --git a/src/include/replication/walreceiver.h b/src/include/replication/walreceiver.h
index 31fa1257ec..7ffa5a58b3 100644
--- a/src/include/replication/walreceiver.h
+++ b/src/include/replication/walreceiver.h
@@ -377,8 +377,9 @@ typedef char *(*walrcv_create_slot_fn) (WalReceiverConn *conn,
  */
 typedef void (*walrcv_alter_slot_fn) (WalReceiverConn *conn,
 									  const char *slotname,
-									  bool failover,
-									  bool two_phase);
+									  const bool *failover,
+									  const bool *two_phase);
+
 
 /*
  * walrcv_get_backend_pid_fn
diff --git a/src/test/subscription/t/021_twophase.pl b/src/test/subscription/t/021_twophase.pl
index da40fcd614..2868d88ddc 100644
--- a/src/test/subscription/t/021_twophase.pl
+++ b/src/test/subscription/t/021_twophase.pl
@@ -375,6 +375,12 @@ $node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub");
 # Verify that the altered subscription reflects the two_phase option.
 ###############################
 
+# Confirm two-phase slot option is enabled before altering
+$result = $node_publisher->safe_psql('postgres',
+	"SELECT two_phase FROM pg_replication_slots WHERE slot_name = 'tap_sub_copy';"
+);
+is($result, qq(t), 'two-phase is enabled');
+
 # Alter subscription two_phase to false
 $node_subscriber->safe_psql('postgres',
 	"ALTER SUBSCRIPTION tap_sub_copy DISABLE;");
@@ -393,7 +399,13 @@ $node_subscriber->wait_for_subscription_sync($node_publisher, $appname_copy);
 $result = $node_subscriber->safe_psql('postgres',
 	"SELECT subtwophasestate FROM pg_subscription WHERE subname = 'tap_sub_copy';"
 );
-is($result, qq(d), 'two-phase should be disabled');
+is($result, qq(d), 'two-phase subscription option should be disabled');
+
+# Make sure that the two-phase slot option is also disabled
+$result = $node_publisher->safe_psql('postgres',
+	"SELECT two_phase FROM pg_replication_slots WHERE slot_name = 'tap_sub_copy';"
+);
+is($result, qq(f), 'two-phase slot option should be disabled');
 
 ###############################
 # Now do a prepare on the publisher.
@@ -414,6 +426,22 @@ $result = $node_subscriber->safe_psql('postgres',
 	"SELECT count(*) FROM pg_prepared_xacts;");
 is($result, qq(0), 'should be no prepared transactions on subscriber');
 
+###############################
+# Toggle the two_phase to "true" before the COMMIT PREPARED.
+#
+# Also, set failover to "true" to test the code path where
+# both two_phase and failover are altered at the same time.
+###############################
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy DISABLE;");
+$node_subscriber->poll_query_until('postgres',
+	"SELECT count(*) = 0 FROM pg_stat_activity WHERE backend_type = 'logical replication worker'"
+);
+$node_subscriber->safe_psql(
+	'postgres', "
+    ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = true, failover = true);
+    ALTER SUBSCRIPTION tap_sub_copy ENABLE;");
+
 ###############################
 # Now commit the insert.
 # Verify that it is replicated.
@@ -428,23 +456,6 @@ $result =
   $node_subscriber->safe_psql('postgres', "SELECT count(*) FROM tab_copy;");
 is($result, qq(3), 'replicated data in subscriber table');
 
-###############################
-# Alter the subscription to two_phase = true.
-# Verify that the altered subscription reflects the two_phase option.
-###############################
-$node_subscriber->safe_psql('postgres',
-	"ALTER SUBSCRIPTION tap_sub_copy DISABLE;");
-$node_subscriber->poll_query_until('postgres',
-	"SELECT count(*) = 0 FROM pg_stat_activity WHERE backend_type = 'logical replication worker'"
-);
-$node_subscriber->safe_psql(
-	'postgres', "
-    ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = true);
-    ALTER SUBSCRIPTION tap_sub_copy ENABLE;");
-
-# Wait for subscription startup
-$node_subscriber->wait_for_subscription_sync($node_publisher, $appname_copy);
-
 # Make sure that the two-phase is enabled on the subscriber
 $result = $node_subscriber->safe_psql('postgres',
 	"SELECT subtwophasestate FROM pg_subscription WHERE subname = 'tap_sub_copy';"
-- 
2.43.0

From 534dbe09fa0f787b2b60d7cf5edd8d87dff378a4 Mon Sep 17 00:00:00 2001
From: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Date: Tue, 9 Jul 2024 08:01:43 +0000
Subject: [PATCH v20 3/3] Notify users to roll back prepared transactions

---
 doc/src/sgml/ref/alter_subscription.sgml | 21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index df44415661..26f423a424 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -233,8 +233,6 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>, and
       <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>.
       Only a superuser can set <literal>password_required = false</literal>.
-      The <literal>two_phase</literal> parameter can only be altered when the
-      subscription is disabled.
      </para>
 
      <para>
@@ -256,6 +254,25 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>
       option is enabled.
      </para>
+
+     <para>
+      The <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>
+      and <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>
+      parameters can only be altered when the subscription is disabled.
+     </para>
+
+     <para>
+      When altering <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>
+      from <literal>true</literal> to <literal>false</literal>,
+      the backend process checks for any incomplete prepared transactions done
+      by the logical replication worker (from when <literal>two_phase</literal>
+      parameter was still <literal>true</literal>) and, if any are found, an
+      error is reported. If this happens, you can resolve prepared transactions
+      on the publisher node or manually roll back them on the subscriber, then
+      try again. After the altering from <literal>true</literal> to
+      <literal>false</literal>, the publisher will replicate transactions again
+      when they are committed.
+     </para>
     </listitem>
    </varlistentry>
 
-- 
2.43.0

From 118569cb257b5681b4dbf0a016fb7894e296bfc9 Mon Sep 17 00:00:00 2001
From: Amit Kapila <akapila@postgresql.org>
Date: Thu, 18 Jul 2024 16:59:53 +0530
Subject: [PATCH v21] Allow altering of two_phase option of a SUBSCRIPTION.

This patch allows the user to alter the 'two_phase' option of a subscriber
provided no uncommitted prepared transactions are pending on that
subscription.

Since the two_phase option is controlled by both the publisher (as a slot
option) and the subscriber (as a subscription option), the slot option
must also be modified.

Regarding the false->true case, the backend process alters the subtwophase
to LOGICALREP_TWOPHASE_STATE_PENDING once. After the subscription is
enabled, a new logical replication worker requests to change the two_phase
option of its slot from pending to true after the initial data
synchronization is done. The code path is the same as the case in which
two_phase is initially set to true, so there is no need to do something
remarkable. However, for the true->false case, the backend must connect to
the publisher and expressly change the parameter because the apply worker
does not alter the option to false. Because this operation cannot be
rolled back, altering the two_phase parameter from "true" to "false"
within a transaction is prohibited.

Author: Hayato Kuroda, Ajin Cherian
---
 doc/src/sgml/protocol.sgml                    |  18 +-
 doc/src/sgml/ref/alter_subscription.sgml      |  28 ++-
 src/backend/access/transam/twophase.c         |  80 +++++++++
 src/backend/commands/subscriptioncmds.c       | 162 ++++++++++++++----
 .../libpqwalreceiver/libpqwalreceiver.c       |  22 ++-
 src/backend/replication/logical/launcher.c    |  10 +-
 src/backend/replication/logical/worker.c      |  25 +--
 src/backend/replication/slot.c                |  44 +++--
 src/backend/replication/walsender.c           |  32 ++--
 src/bin/psql/tab-complete.c                   |   2 +-
 src/include/access/twophase.h                 |   5 +
 src/include/replication/slot.h                |   3 +-
 src/include/replication/walreceiver.h         |  12 +-
 src/include/replication/worker_internal.h     |   3 +-
 src/test/regress/expected/subscription.out    |   5 +-
 src/test/regress/sql/subscription.sql         |   5 +-
 src/test/subscription/t/021_twophase.pl       |  97 ++++++++++-
 17 files changed, 439 insertions(+), 114 deletions(-)

diff --git a/doc/src/sgml/protocol.sgml b/doc/src/sgml/protocol.sgml
index 1b27d0a547..79cd599692 100644
--- a/doc/src/sgml/protocol.sgml
+++ b/doc/src/sgml/protocol.sgml
@@ -2192,7 +2192,23 @@ psql "dbname=postgres replication=database" -c "IDENTIFY_SYSTEM;"
        </varlistentry>
       </variablelist>
 
-      <para>The following option is supported:</para>
+      <para>The following options are supported:</para>
+
+      <variablelist>
+       <varlistentry>
+        <term><literal>TWO_PHASE [ <replaceable class="parameter">boolean</replaceable> ]</literal></term>
+        <listitem>
+         <para>
+          If true, this logical replication slot supports decoding of two-phase
+          commit. With this option, commands related to two-phase commit such as
+          <literal>PREPARE TRANSACTION</literal>, <literal>COMMIT PREPARED</literal>
+          and <literal>ROLLBACK PREPARED</literal> are decoded and transmitted.
+          The transaction will be decoded and transmitted at
+          <literal>PREPARE TRANSACTION</literal> time.
+         </para>
+        </listitem>
+       </varlistentry>
+      </variablelist>
 
       <variablelist>
        <varlistentry>
diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index 476f195622..70de81a6c9 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -68,8 +68,9 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
   <para>
    Commands <command>ALTER SUBSCRIPTION ... REFRESH PUBLICATION</command>,
    <command>ALTER SUBSCRIPTION ... {SET|ADD|DROP} PUBLICATION ...</command>
-   with <literal>refresh</literal> option as <literal>true</literal> and
-   <command>ALTER SUBSCRIPTION ... SET (failover = true|false)</command>
+   with <literal>refresh</literal> option as <literal>true</literal>,
+   <command>ALTER SUBSCRIPTION ... SET (failover = true|false)</command> and
+   <command>ALTER SUBSCRIPTION ... SET (two_phase = false)</command>
    cannot be executed inside a transaction block.
 
    These commands also cannot be executed when the subscription has
@@ -228,8 +229,9 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-disable-on-error"><literal>disable_on_error</literal></link>,
       <link linkend="sql-createsubscription-params-with-password-required"><literal>password_required</literal></link>,
       <link linkend="sql-createsubscription-params-with-run-as-owner"><literal>run_as_owner</literal></link>,
-      <link linkend="sql-createsubscription-params-with-origin"><literal>origin</literal></link>, and
-      <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>.
+      <link linkend="sql-createsubscription-params-with-origin"><literal>origin</literal></link>,
+      <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>, and
+      <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>.
       Only a superuser can set <literal>password_required = false</literal>.
      </para>
 
@@ -252,6 +254,24 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>
       option is enabled.
      </para>
+
+     <para>
+      The <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>
+      and <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>
+      parameters can only be altered when the subscription is disabled.
+     </para>
+
+     <para>
+      When altering <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>
+      from <literal>true</literal> to <literal>false</literal>, the backend
+      process reports and an error if any prepared transactions done by the
+      logical replication worker (from when <literal>two_phase</literal>
+      parameter was still <literal>true</literal>) are found. You can resolve
+      prepared transactions on the publisher node, or manually roll back them
+      on the subscriber, and then try again. After the <literal>two_phase</literal>
+      option is changed from <literal>true</literal> to <literal>false</literal>,
+      the publisher will replicate the transactions again when they are committed.
+     </para>
     </listitem>
    </varlistentry>
 
diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index 9a8257fcaf..90df32f177 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -2681,3 +2681,83 @@ LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 	LWLockRelease(TwoPhaseStateLock);
 	return found;
 }
+
+/*
+ * TwoPhaseTransactionGid
+ *		Form the prepared transaction GID for two_phase transactions.
+ *
+ * Return the GID in the supplied buffer.
+ */
+void
+TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid_res, int szgid)
+{
+	Assert(subid != InvalidRepOriginId);
+
+	if (!TransactionIdIsValid(xid))
+		ereport(ERROR,
+				(errcode(ERRCODE_PROTOCOL_VIOLATION),
+				 errmsg_internal("invalid two-phase transaction ID")));
+
+	snprintf(gid_res, szgid, "pg_gid_%u_%u", subid, xid);
+}
+
+/*
+ * IsTwoPhaseTransactionGidForSubid
+ *		Check whether the given GID (as formed by TwoPhaseTransactionGid) is
+ *		for the specified 'subid'.
+ */
+static bool
+IsTwoPhaseTransactionGidForSubid(Oid subid, char *gid)
+{
+	int			ret;
+	Oid			subid_from_gid;
+	TransactionId xid_from_gid;
+	char		gid_generated[GIDSIZE];
+
+	/* Extract the subid and xid from the given GID */
+	ret = sscanf(gid, "pg_gid_%u_%u", &subid_from_gid, &xid_from_gid);
+
+	/*
+	 * Check that the given GID has expected format, and at least the subid
+	 * matches.
+	 */
+	if (ret != 2 || subid != subid_from_gid)
+		return false;
+
+	/*
+	 * Reconstruct a temporary GID based on the subid and xid extracted from
+	 * the given GID and check whether the temporary GID and the given GID
+	 * match.
+	 */
+	TwoPhaseTransactionGid(subid, xid_from_gid, gid_generated,
+						   sizeof(gid_generated));
+
+	return strcmp(gid, gid_generated) == 0;
+}
+
+/*
+ * LookupGXactBySubid
+ *		Check if the prepared transaction done by apply worker exists.
+ */
+bool
+LookupGXactBySubid(Oid subid)
+{
+	bool		found = false;
+
+	LWLockAcquire(TwoPhaseStateLock, LW_SHARED);
+	for (int i = 0; i < TwoPhaseState->numPrepXacts; i++)
+	{
+		GlobalTransaction gxact = TwoPhaseState->prepXacts[i];
+
+		/* Ignore not-yet-valid GIDs. */
+		if (gxact->valid &&
+			IsTwoPhaseTransactionGidForSubid(subid, gxact->gid))
+		{
+			found = true;
+			break;
+		}
+	}
+	LWLockRelease(TwoPhaseStateLock);
+
+	return found;
+}
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index 16d83b3253..2e9f329d0e 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -16,6 +16,7 @@
 
 #include "access/htup_details.h"
 #include "access/table.h"
+#include "access/twophase.h"
 #include "access/xact.h"
 #include "catalog/catalog.h"
 #include "catalog/dependency.h"
@@ -109,6 +110,8 @@ static void check_publications_origin(WalReceiverConn *wrconn,
 static void check_duplicates_in_publist(List *publist, Datum *datums);
 static List *merge_publications(List *oldpublist, List *newpublist, bool addpub, const char *subname);
 static void ReportSlotConnectionError(List *rstates, Oid subid, char *slotname, char *err);
+static void CheckAlterSubOption(Subscription *sub, const char *option,
+								bool slot_needs_update, bool isTopLevel);
 
 
 /*
@@ -259,21 +262,9 @@ parse_subscription_options(ParseState *pstate, List *stmt_options,
 			opts->specified_opts |= SUBOPT_STREAMING;
 			opts->streaming = defGetStreamingMode(defel);
 		}
-		else if (strcmp(defel->defname, "two_phase") == 0)
+		else if (IsSet(supported_opts, SUBOPT_TWOPHASE_COMMIT) &&
+				 strcmp(defel->defname, "two_phase") == 0)
 		{
-			/*
-			 * Do not allow toggling of two_phase option. Doing so could cause
-			 * missing of transactions and lead to an inconsistent replica.
-			 * See comments atop worker.c
-			 *
-			 * Note: Unsupported twophase indicates that this call originated
-			 * from AlterSubscription.
-			 */
-			if (!IsSet(supported_opts, SUBOPT_TWOPHASE_COMMIT))
-				ereport(ERROR,
-						(errcode(ERRCODE_SYNTAX_ERROR),
-						 errmsg("unrecognized subscription parameter: \"%s\"", defel->defname)));
-
 			if (IsSet(opts->specified_opts, SUBOPT_TWOPHASE_COMMIT))
 				errorConflictingDefElem(defel, pstate);
 
@@ -1079,6 +1070,55 @@ AlterSubscription_refresh(Subscription *sub, bool copy_data,
 		table_close(rel, NoLock);
 }
 
+/*
+ * Common checks for altering failover and two_phase option
+ */
+static void
+CheckAlterSubOption(Subscription *sub, const char *option,
+					bool slot_needs_update, bool isTopLevel)
+{
+	/*
+	 * The checks in this function are required only for failover and two_phase
+	 * options.
+	 */
+	Assert(strcmp(option, "failover") == 0 ||
+		   strcmp(option, "two_phase") == 0);
+
+	/*
+	 * Do not allow changing the option if the subscription is enabled. This
+	 * is because both failover and two_phase options of the slot on the
+	 * publisher cannot be modified if the slot is currently acquired by the
+	 * existing walsender.
+	 */
+	if (sub->enabled)
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("cannot set %s for enabled subscription",
+						option)));
+
+	if (slot_needs_update)
+	{
+		StringInfoData cmd;
+
+		/*
+		 * A valid slot must be associated with the subscription for us to modify
+		 * any of the slot's properties.
+		 */
+		if (!sub->slotname)
+			ereport(ERROR,
+					(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+					 errmsg("cannot set %s for a subscription that does not have a slot name",
+							option)));
+
+		/* The changed option of the slot can't be rolled back. */
+		initStringInfo(&cmd);
+		appendStringInfo(&cmd, "ALTER SUBSCRIPTION ... SET (%s)", option);
+
+		PreventInTransactionBlock(isTopLevel, cmd.data);
+		pfree(cmd.data);
+	}
+}
+
 /*
  * Alter the existing subscription.
  */
@@ -1094,6 +1134,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 	HeapTuple	tup;
 	Oid			subid;
 	bool		update_tuple = false;
+	bool		update_failover = false;
+	bool		update_two_phase = false;
 	Subscription *sub;
 	Form_pg_subscription form;
 	bits32		supported_opts;
@@ -1145,7 +1187,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 			{
 				supported_opts = (SUBOPT_SLOT_NAME |
 								  SUBOPT_SYNCHRONOUS_COMMIT | SUBOPT_BINARY |
-								  SUBOPT_STREAMING | SUBOPT_DISABLE_ON_ERR |
+								  SUBOPT_STREAMING | SUBOPT_TWOPHASE_COMMIT |
+								  SUBOPT_DISABLE_ON_ERR |
 								  SUBOPT_PASSWORD_REQUIRED |
 								  SUBOPT_RUN_AS_OWNER | SUBOPT_FAILOVER |
 								  SUBOPT_ORIGIN);
@@ -1227,31 +1270,80 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 					replaces[Anum_pg_subscription_subrunasowner - 1] = true;
 				}
 
-				if (IsSet(opts.specified_opts, SUBOPT_FAILOVER))
+				if (IsSet(opts.specified_opts, SUBOPT_TWOPHASE_COMMIT))
 				{
-					if (!sub->slotname)
+					/*
+					 * We need to update both the slot and the subscription for
+					 * two_phase option. We can enable the two_phase option for
+					 * a slot only once the initial data syncronization is
+					 * done. This is to avoid missing some data as explained in
+					 * comments atop worker.c.
+					 */
+					update_two_phase = !opts.twophase;
+
+					CheckAlterSubOption(sub, "two_phase", update_two_phase,
+										isTopLevel);
+
+					/*
+					 * Modifying the two_phase slot option requires a slot
+					 * lookup by slot name, so changing the slot name at the
+					 * same time is not allowed.
+					 */
+					if (update_two_phase &&
+						IsSet(opts.specified_opts, SUBOPT_SLOT_NAME))
+						ereport(ERROR,
+								(errcode(ERRCODE_SYNTAX_ERROR),
+								 errmsg("slot_name and two_phase cannot be altered at the same time")));
+
+					/*
+					 * Note that workers may still survive even if the
+					 * subscription has been disabled.
+					 *
+					 * Ensure workers have already been exited to avoid getting
+					 * prepared transactions while we are disabling two_phase
+					 * option. Otherwise, the changes of already prepared
+					 * transactions can be replicated again along with its
+					 * corresponding commit leading to duplicate data or
+					 * errors.
+					 */
+					if (logicalrep_workers_find(subid, true, true))
 						ereport(ERROR,
 								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-								 errmsg("cannot set %s for a subscription that does not have a slot name",
-										"failover")));
+								 errmsg("cannot alter two_phase when logical replication worker is still running"),
+								 errhint("Try again after some time.")));
 
 					/*
-					 * Do not allow changing the failover state if the
-					 * subscription is enabled. This is because the failover
-					 * state of the slot on the publisher cannot be modified
-					 * if the slot is currently acquired by the apply worker.
+					 * two_phase cannot be disabled if there are any
+					 * uncommitted prepared transactions present otherwise it
+					 * can lead to duplicate data or errors as explained in the
+					 * comment above.
 					 */
-					if (sub->enabled)
+					if (update_two_phase &&
+						sub->twophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
+						LookupGXactBySubid(subid))
 						ereport(ERROR,
 								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-								 errmsg("cannot set %s for enabled subscription",
-										"failover")));
+								 errmsg("cannot disable two_phase when prepared transactions are present"),
+								 errhint("Resolve these transactions and try again.")));
+
+					/* Change system catalog accordingly */
+					values[Anum_pg_subscription_subtwophasestate - 1] =
+						CharGetDatum(opts.twophase ?
+									 LOGICALREP_TWOPHASE_STATE_PENDING :
+									 LOGICALREP_TWOPHASE_STATE_DISABLED);
+					replaces[Anum_pg_subscription_subtwophasestate - 1] = true;
+				}
 
+				if (IsSet(opts.specified_opts, SUBOPT_FAILOVER))
+				{
 					/*
-					 * The changed failover option of the slot can't be rolled
-					 * back.
+					 * Samilar to two_phase, we need to update the failover
+					 * option for the slot and the subscription.
 					 */
-					PreventInTransactionBlock(isTopLevel, "ALTER SUBSCRIPTION ... SET (failover)");
+					update_failover = true;
+
+					CheckAlterSubOption(sub, "failover", update_failover,
+										isTopLevel);
 
 					values[Anum_pg_subscription_subfailover - 1] =
 						BoolGetDatum(opts.failover);
@@ -1501,13 +1593,13 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 	}
 
 	/*
-	 * Try to acquire the connection necessary for altering slot.
+	 * Try to acquire the connection necessary for altering slot, if needed.
 	 *
 	 * This has to be at the end because otherwise if there is an error while
 	 * doing the database operations we won't be able to rollback altered
 	 * slot.
 	 */
-	if (replaces[Anum_pg_subscription_subfailover - 1])
+	if (update_failover || update_two_phase)
 	{
 		bool		must_use_password;
 		char	   *err;
@@ -1528,7 +1620,9 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 
 		PG_TRY();
 		{
-			walrcv_alter_slot(wrconn, sub->slotname, opts.failover);
+			walrcv_alter_slot(wrconn, sub->slotname,
+							  update_failover ? &opts.failover : NULL,
+							  update_two_phase ? &opts.twophase : NULL);
 		}
 		PG_FINALLY();
 		{
@@ -1675,9 +1769,7 @@ DropSubscription(DropSubscriptionStmt *stmt, bool isTopLevel)
 	 * New workers won't be started because we hold an exclusive lock on the
 	 * subscription till the end of the transaction.
 	 */
-	LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
-	subworkers = logicalrep_workers_find(subid, false);
-	LWLockRelease(LogicalRepWorkerLock);
+	subworkers = logicalrep_workers_find(subid, false, true);
 	foreach(lc, subworkers)
 	{
 		LogicalRepWorker *w = (LogicalRepWorker *) lfirst(lc);
diff --git a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
index 6c42c209d2..97f957cd87 100644
--- a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
+++ b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
@@ -80,7 +80,7 @@ static char *libpqrcv_create_slot(WalReceiverConn *conn,
 								  CRSSnapshotAction snapshot_action,
 								  XLogRecPtr *lsn);
 static void libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-								bool failover);
+								const bool *failover, const bool *two_phase);
 static pid_t libpqrcv_get_backend_pid(WalReceiverConn *conn);
 static WalRcvExecResult *libpqrcv_exec(WalReceiverConn *conn,
 									   const char *query,
@@ -1121,15 +1121,27 @@ libpqrcv_create_slot(WalReceiverConn *conn, const char *slotname,
  */
 static void
 libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-					bool failover)
+					const bool *failover, const bool *two_phase)
 {
 	StringInfoData cmd;
 	PGresult   *res;
 
 	initStringInfo(&cmd);
-	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( FAILOVER %s )",
-					 quote_identifier(slotname),
-					 failover ? "true" : "false");
+	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( ",
+					 quote_identifier(slotname));
+
+	if (failover)
+		appendStringInfo(&cmd, "FAILOVER %s",
+						 *failover ? "true" : "false");
+
+	if (failover && two_phase)
+		appendStringInfo(&cmd, ", ");
+
+	if (two_phase)
+		appendStringInfo(&cmd, "TWO_PHASE %s",
+						 *two_phase ? "true" : "false");
+
+	appendStringInfoString(&cmd, " );");
 
 	res = libpqrcv_PQexec(conn->streamConn, cmd.data);
 	pfree(cmd.data);
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 27c3a91fb7..c566d50a07 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -272,11 +272,14 @@ logicalrep_worker_find(Oid subid, Oid relid, bool only_running)
  * the subscription, instead of just one.
  */
 List *
-logicalrep_workers_find(Oid subid, bool only_running)
+logicalrep_workers_find(Oid subid, bool only_running, bool acquire_lock)
 {
 	int			i;
 	List	   *res = NIL;
 
+	if (acquire_lock)
+		LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
+
 	Assert(LWLockHeldByMe(LogicalRepWorkerLock));
 
 	/* Search for attached worker for a given subscription id. */
@@ -288,6 +291,9 @@ logicalrep_workers_find(Oid subid, bool only_running)
 			res = lappend(res, w);
 	}
 
+	if (acquire_lock)
+		LWLockRelease(LogicalRepWorkerLock);
+
 	return res;
 }
 
@@ -759,7 +765,7 @@ logicalrep_worker_detach(void)
 
 		LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
 
-		workers = logicalrep_workers_find(MyLogicalRepWorker->subid, true);
+		workers = logicalrep_workers_find(MyLogicalRepWorker->subid, true, false);
 		foreach(lc, workers)
 		{
 			LogicalRepWorker *w = (LogicalRepWorker *) lfirst(lc);
diff --git a/src/backend/replication/logical/worker.c b/src/backend/replication/logical/worker.c
index c0bda6269b..6c798cd5b4 100644
--- a/src/backend/replication/logical/worker.c
+++ b/src/backend/replication/logical/worker.c
@@ -401,9 +401,6 @@ static void apply_handle_tuple_routing(ApplyExecutionData *edata,
 									   LogicalRepTupleData *newtup,
 									   CmdType operation);
 
-/* Compute GID for two_phase transactions */
-static void TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid, int szgid);
-
 /* Functions for skipping changes */
 static void maybe_start_skipping_changes(XLogRecPtr finish_lsn);
 static void stop_skipping_changes(void);
@@ -3911,7 +3908,7 @@ maybe_reread_subscription(void)
 	/* !slotname should never happen when enabled is true. */
 	Assert(newsub->slotname);
 
-	/* two-phase should not be altered */
+	/* two-phase cannot be altered while the worker exists */
 	Assert(newsub->twophasestate == MySubscription->twophasestate);
 
 	/*
@@ -4396,24 +4393,6 @@ cleanup_subxact_info()
 	subxact_data.nsubxacts_max = 0;
 }
 
-/*
- * Form the prepared transaction GID for two_phase transactions.
- *
- * Return the GID in the supplied buffer.
- */
-static void
-TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid, int szgid)
-{
-	Assert(subid != InvalidRepOriginId);
-
-	if (!TransactionIdIsValid(xid))
-		ereport(ERROR,
-				(errcode(ERRCODE_PROTOCOL_VIOLATION),
-				 errmsg_internal("invalid two-phase transaction ID")));
-
-	snprintf(gid, szgid, "pg_gid_%u_%u", subid, xid);
-}
-
 /*
  * Common function to run the apply loop with error handling. Disable the
  * subscription, if necessary.
@@ -5014,7 +4993,7 @@ AtEOXact_LogicalRepWorkers(bool isCommit)
 			List	   *workers;
 			ListCell   *lc2;
 
-			workers = logicalrep_workers_find(subid, true);
+			workers = logicalrep_workers_find(subid, true, false);
 			foreach(lc2, workers)
 			{
 				LogicalRepWorker *worker = (LogicalRepWorker *) lfirst(lc2);
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index baf9b89dc4..90494cb858 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -804,9 +804,12 @@ ReplicationSlotDrop(const char *name, bool nowait)
  * Change the definition of the slot identified by the specified name.
  */
 void
-ReplicationSlotAlter(const char *name, bool failover)
+ReplicationSlotAlter(const char *name, bool *failover, bool *two_phase)
 {
+	bool		update_slot = false;
+
 	Assert(MyReplicationSlot == NULL);
+	Assert(failover || two_phase);
 
 	ReplicationSlotAcquire(name, false);
 
@@ -832,28 +835,45 @@ ReplicationSlotAlter(const char *name, bool failover)
 		 * Do not allow users to enable failover on the standby as we do not
 		 * support sync to the cascading standby.
 		 */
-		if (failover)
+		if (failover && *failover)
 			ereport(ERROR,
 					errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 					errmsg("cannot enable failover for a replication slot"
 						   " on the standby"));
 	}
 
-	/*
-	 * Do not allow users to enable failover for temporary slots as we do not
-	 * support syncing temporary slots to the standby.
-	 */
-	if (failover && MyReplicationSlot->data.persistency == RS_TEMPORARY)
-		ereport(ERROR,
-				errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-				errmsg("cannot enable failover for a temporary replication slot"));
+	if (failover)
+	{
+		/*
+		 * Do not allow users to enable failover for temporary slots as we do
+		 * not support syncing temporary slots to the standby.
+		 */
+		if (*failover && MyReplicationSlot->data.persistency == RS_TEMPORARY)
+			ereport(ERROR,
+					errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+					errmsg("cannot enable failover for a temporary replication slot"));
+
+		if (MyReplicationSlot->data.failover != *failover)
+		{
+			SpinLockAcquire(&MyReplicationSlot->mutex);
+			MyReplicationSlot->data.failover = *failover;
+			SpinLockRelease(&MyReplicationSlot->mutex);
+
+			update_slot = true;
+		}
+	}
 
-	if (MyReplicationSlot->data.failover != failover)
+	if (two_phase && MyReplicationSlot->data.two_phase != *two_phase)
 	{
 		SpinLockAcquire(&MyReplicationSlot->mutex);
-		MyReplicationSlot->data.failover = failover;
+		MyReplicationSlot->data.two_phase = *two_phase;
 		SpinLockRelease(&MyReplicationSlot->mutex);
 
+		update_slot = true;
+	}
+
+	if (update_slot)
+	{
 		ReplicationSlotMarkDirty();
 		ReplicationSlotSave();
 	}
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index ca205594bd..c5f1009f37 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1407,12 +1407,15 @@ DropReplicationSlot(DropReplicationSlotCmd *cmd)
 }
 
 /*
- * Process extra options given to ALTER_REPLICATION_SLOT.
+ * Change the definition of a replication slot.
  */
 static void
-ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd, bool *failover)
+AlterReplicationSlot(AlterReplicationSlotCmd *cmd)
 {
 	bool		failover_given = false;
+	bool		two_phase_given = false;
+	bool		failover;
+	bool		two_phase;
 
 	/* Parse options */
 	foreach_ptr(DefElem, defel, cmd->options)
@@ -1424,23 +1427,24 @@ ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd, bool *failover)
 						(errcode(ERRCODE_SYNTAX_ERROR),
 						 errmsg("conflicting or redundant options")));
 			failover_given = true;
-			*failover = defGetBoolean(defel);
+			failover = defGetBoolean(defel);
+		}
+		else if (strcmp(defel->defname, "two_phase") == 0)
+		{
+			if (two_phase_given)
+				ereport(ERROR,
+						(errcode(ERRCODE_SYNTAX_ERROR),
+						 errmsg("conflicting or redundant options")));
+			two_phase_given = true;
+			two_phase = defGetBoolean(defel);
 		}
 		else
 			elog(ERROR, "unrecognized option: %s", defel->defname);
 	}
-}
-
-/*
- * Change the definition of a replication slot.
- */
-static void
-AlterReplicationSlot(AlterReplicationSlotCmd *cmd)
-{
-	bool		failover = false;
 
-	ParseAlterReplSlotOptions(cmd, &failover);
-	ReplicationSlotAlter(cmd->slotname, failover);
+	ReplicationSlotAlter(cmd->slotname,
+						 failover_given ? &failover : NULL,
+						 two_phase_given ? &two_phase : NULL);
 }
 
 /*
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
index d453e224d9..891face1b6 100644
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -1948,7 +1948,7 @@ psql_completion(const char *text, int start, int end)
 	else if (HeadMatches("ALTER", "SUBSCRIPTION", MatchAny) && TailMatches("SET", "("))
 		COMPLETE_WITH("binary", "disable_on_error", "failover", "origin",
 					  "password_required", "run_as_owner", "slot_name",
-					  "streaming", "synchronous_commit");
+					  "streaming", "synchronous_commit", "two_phase");
 	/* ALTER SUBSCRIPTION <name> SKIP ( */
 	else if (HeadMatches("ALTER", "SUBSCRIPTION", MatchAny) && TailMatches("SKIP", "("))
 		COMPLETE_WITH("lsn");
diff --git a/src/include/access/twophase.h b/src/include/access/twophase.h
index 56248c0006..b85b65c604 100644
--- a/src/include/access/twophase.h
+++ b/src/include/access/twophase.h
@@ -62,4 +62,9 @@ extern void PrepareRedoRemove(TransactionId xid, bool giveWarning);
 extern void restoreTwoPhaseData(void);
 extern bool LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 						TimestampTz origin_prepare_timestamp);
+
+extern void TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid_res,
+								   int szgid);
+extern bool LookupGXactBySubid(Oid subid);
+
 #endif							/* TWOPHASE_H */
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index c9675ee87c..cde164472a 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -243,7 +243,8 @@ extern void ReplicationSlotCreate(const char *name, bool db_specific,
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
 extern void ReplicationSlotDropAcquired(void);
-extern void ReplicationSlotAlter(const char *name, bool failover);
+extern void ReplicationSlotAlter(const char *name, bool *failover,
+								 bool *two_phase);
 
 extern void ReplicationSlotAcquire(const char *name, bool nowait);
 extern void ReplicationSlotRelease(void);
diff --git a/src/include/replication/walreceiver.h b/src/include/replication/walreceiver.h
index 12f71fa99b..7ffa5a58b3 100644
--- a/src/include/replication/walreceiver.h
+++ b/src/include/replication/walreceiver.h
@@ -372,12 +372,14 @@ typedef char *(*walrcv_create_slot_fn) (WalReceiverConn *conn,
 /*
  * walrcv_alter_slot_fn
  *
- * Change the definition of a replication slot. Currently, it only supports
- * changing the failover property of the slot.
+ * Change the definition of a replication slot. Currently, it supports
+ * changing the failover and the two_phase property of the slot.
  */
 typedef void (*walrcv_alter_slot_fn) (WalReceiverConn *conn,
 									  const char *slotname,
-									  bool failover);
+									  const bool *failover,
+									  const bool *two_phase);
+
 
 /*
  * walrcv_get_backend_pid_fn
@@ -455,8 +457,8 @@ extern PGDLLIMPORT WalReceiverFunctionsType *WalReceiverFunctions;
 	WalReceiverFunctions->walrcv_send(conn, buffer, nbytes)
 #define walrcv_create_slot(conn, slotname, temporary, two_phase, failover, snapshot_action, lsn) \
 	WalReceiverFunctions->walrcv_create_slot(conn, slotname, temporary, two_phase, failover, snapshot_action, lsn)
-#define walrcv_alter_slot(conn, slotname, failover) \
-	WalReceiverFunctions->walrcv_alter_slot(conn, slotname, failover)
+#define walrcv_alter_slot(conn, slotname, failover, two_phase) \
+	WalReceiverFunctions->walrcv_alter_slot(conn, slotname, failover, two_phase)
 #define walrcv_get_backend_pid(conn) \
 	WalReceiverFunctions->walrcv_get_backend_pid(conn)
 #define walrcv_exec(conn, exec, nRetTypes, retTypes) \
diff --git a/src/include/replication/worker_internal.h b/src/include/replication/worker_internal.h
index 515aefd519..9646261d7e 100644
--- a/src/include/replication/worker_internal.h
+++ b/src/include/replication/worker_internal.h
@@ -240,7 +240,8 @@ extern PGDLLIMPORT bool InitializingApplyWorker;
 extern void logicalrep_worker_attach(int slot);
 extern LogicalRepWorker *logicalrep_worker_find(Oid subid, Oid relid,
 												bool only_running);
-extern List *logicalrep_workers_find(Oid subid, bool only_running);
+extern List *logicalrep_workers_find(Oid subid, bool only_running,
+									 bool acquire_lock);
 extern bool logicalrep_worker_launch(LogicalRepWorkerType wtype,
 									 Oid dbid, Oid subid, const char *subname,
 									 Oid userid, Oid relid,
diff --git a/src/test/regress/expected/subscription.out b/src/test/regress/expected/subscription.out
index 5c2f1ee517..17d48b1685 100644
--- a/src/test/regress/expected/subscription.out
+++ b/src/test/regress/expected/subscription.out
@@ -377,10 +377,7 @@ HINT:  To initiate replication, you must manually create the replication slot, e
  regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | p                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
---fail - alter of two_phase option not supported.
-ALTER SUBSCRIPTION regress_testsub SET (two_phase = false);
-ERROR:  unrecognized subscription parameter: "two_phase"
--- but can alter streaming when two_phase enabled
+-- we can alter streaming when two_phase enabled
 ALTER SUBSCRIPTION regress_testsub SET (streaming = true);
 \dRs+
                                                                                                                 List of subscriptions
diff --git a/src/test/regress/sql/subscription.sql b/src/test/regress/sql/subscription.sql
index 3e5ba4cb8c..007c9e7037 100644
--- a/src/test/regress/sql/subscription.sql
+++ b/src/test/regress/sql/subscription.sql
@@ -256,10 +256,7 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUBLICATION testpub WITH (connect = false, two_phase = true);
 
 \dRs+
---fail - alter of two_phase option not supported.
-ALTER SUBSCRIPTION regress_testsub SET (two_phase = false);
-
--- but can alter streaming when two_phase enabled
+-- we can alter streaming when two_phase enabled
 ALTER SUBSCRIPTION regress_testsub SET (streaming = true);
 
 \dRs+
diff --git a/src/test/subscription/t/021_twophase.pl b/src/test/subscription/t/021_twophase.pl
index 9437cd4c3b..2868d88ddc 100644
--- a/src/test/subscription/t/021_twophase.pl
+++ b/src/test/subscription/t/021_twophase.pl
@@ -367,6 +367,101 @@ $result =
   $node_subscriber->safe_psql('postgres', "SELECT count(*) FROM tab_copy;");
 is($result, qq(2), 'replicated data in subscriber table');
 
+# Clean up
+$node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub");
+
+###############################
+# Alter the subscription to two_phase = false.
+# Verify that the altered subscription reflects the two_phase option.
+###############################
+
+# Confirm two-phase slot option is enabled before altering
+$result = $node_publisher->safe_psql('postgres',
+	"SELECT two_phase FROM pg_replication_slots WHERE slot_name = 'tap_sub_copy';"
+);
+is($result, qq(t), 'two-phase is enabled');
+
+# Alter subscription two_phase to false
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy DISABLE;");
+$node_subscriber->poll_query_until('postgres',
+	"SELECT count(*) = 0 FROM pg_stat_activity WHERE backend_type = 'logical replication worker'"
+);
+$node_subscriber->safe_psql(
+	'postgres', "
+    ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = false);
+    ALTER SUBSCRIPTION tap_sub_copy ENABLE;");
+
+# Wait for subscription startup
+$node_subscriber->wait_for_subscription_sync($node_publisher, $appname_copy);
+
+# Make sure that the two-phase is disabled on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT subtwophasestate FROM pg_subscription WHERE subname = 'tap_sub_copy';"
+);
+is($result, qq(d), 'two-phase subscription option should be disabled');
+
+# Make sure that the two-phase slot option is also disabled
+$result = $node_publisher->safe_psql('postgres',
+	"SELECT two_phase FROM pg_replication_slots WHERE slot_name = 'tap_sub_copy';"
+);
+is($result, qq(f), 'two-phase slot option should be disabled');
+
+###############################
+# Now do a prepare on the publisher.
+# Verify that it is not replicated.
+###############################
+$node_publisher->safe_psql(
+	'postgres', qq{
+    BEGIN;
+    INSERT INTO tab_copy VALUES (100);
+    PREPARE TRANSACTION 'newgid';
+	});
+
+# Wait for the subscriber to catchup
+$node_publisher->wait_for_catchup($appname_copy);
+
+# Make sure there are no prepared transactions on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT count(*) FROM pg_prepared_xacts;");
+is($result, qq(0), 'should be no prepared transactions on subscriber');
+
+###############################
+# Toggle the two_phase to "true" before the COMMIT PREPARED.
+#
+# Also, set failover to "true" to test the code path where
+# both two_phase and failover are altered at the same time.
+###############################
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy DISABLE;");
+$node_subscriber->poll_query_until('postgres',
+	"SELECT count(*) = 0 FROM pg_stat_activity WHERE backend_type = 'logical replication worker'"
+);
+$node_subscriber->safe_psql(
+	'postgres', "
+    ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = true, failover = true);
+    ALTER SUBSCRIPTION tap_sub_copy ENABLE;");
+
+###############################
+# Now commit the insert.
+# Verify that it is replicated.
+###############################
+$node_publisher->safe_psql('postgres', "COMMIT PREPARED 'newgid';");
+
+# Wait for the subscriber to catchup
+$node_publisher->wait_for_catchup($appname_copy);
+
+# Make sure that the committed transaction is replicated.
+$result =
+  $node_subscriber->safe_psql('postgres', "SELECT count(*) FROM tab_copy;");
+is($result, qq(3), 'replicated data in subscriber table');
+
+# Make sure that the two-phase is enabled on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT subtwophasestate FROM pg_subscription WHERE subname = 'tap_sub_copy';"
+);
+is($result, qq(e), 'two-phase should be enabled');
+
 $node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub_copy;");
 $node_publisher->safe_psql('postgres', "DROP PUBLICATION tap_pub_copy;");
 
@@ -374,8 +469,6 @@ $node_publisher->safe_psql('postgres', "DROP PUBLICATION tap_pub_copy;");
 # check all the cleanup
 ###############################
 
-$node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub");
-
 $result = $node_subscriber->safe_psql('postgres',
 	"SELECT count(*) FROM pg_subscription");
 is($result, qq(0), 'check subscription was dropped on subscriber');
-- 
2.39.1

diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index 90df32f..da97836 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -2712,7 +2712,7 @@ IsTwoPhaseTransactionGidForSubid(Oid subid, char *gid)
 	int			ret;
 	Oid			subid_from_gid;
 	TransactionId xid_from_gid;
-	char		gid_generated[GIDSIZE];
+	char		gid_tmp[GIDSIZE];
 
 	/* Extract the subid and xid from the given GID */
 	ret = sscanf(gid, "pg_gid_%u_%u", &subid_from_gid, &xid_from_gid);
@@ -2729,10 +2729,9 @@ IsTwoPhaseTransactionGidForSubid(Oid subid, char *gid)
 	 * the given GID and check whether the temporary GID and the given GID
 	 * match.
 	 */
-	TwoPhaseTransactionGid(subid, xid_from_gid, gid_generated,
-						   sizeof(gid_generated));
+	TwoPhaseTransactionGid(subid, xid_from_gid, gid_tmp, sizeof(gid_tmp));
 
-	return strcmp(gid, gid_generated) == 0;
+	return strcmp(gid, gid_tmp) == 0;
 }
 
 /*
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index 2e9f329..5f11235 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -1071,7 +1071,7 @@ AlterSubscription_refresh(Subscription *sub, bool copy_data,
 }
 
 /*
- * Common checks for altering failover and two_phase option
+ * Common checks for altering failover and two_phase options.
  */
 static void
 CheckAlterSubOption(Subscription *sub, const char *option,
@@ -1337,8 +1337,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 				if (IsSet(opts.specified_opts, SUBOPT_FAILOVER))
 				{
 					/*
-					 * Samilar to two_phase, we need to update the failover
-					 * option for the slot and the subscription.
+					 * Similar to the two_phase case above, we need to update
+					 * the failover option for the slot and the subscription.
 					 */
 					update_failover = true;
 

From 6949bda13f4b55d35fa3743cc0ce574268e1a323 Mon Sep 17 00:00:00 2001
From: Amit Kapila <akapila@postgresql.org>
Date: Thu, 18 Jul 2024 16:59:53 +0530
Subject: [PATCH v23] Allow altering of two_phase option for a SUBSCRIPTION.

The two_phase option is controlled by both the publisher (as a slot
option) and the subscriber (as a subscription option), so, the slot option
must also be modified.

Changing the 'two_phase' option for a subscription from 'true' to 'false'
is permitted only when there are no pending prepared transactions
corresponding to that subscription. Otherwise, the changes of already
prepared transactions can be replicated again along with its corresponding
commit leading to duplicate data or errors.

We can change the 'two_phase' option for a subscription from 'false' to
'true' only once the initial data synchronization is done to avoid data
loss. So, this is performed later by the logical replication worker.

Author: Hayato Kuroda, Ajin Cherian, Amit Kapila
Reviewed-by: Peter Smith, Hou Zhijie, Amit Kapila, Vitaly Davydov, Vignesh C
Discussion: https://postgr.es/m/8fab8-65d74c80-1-2f28e880@39088166
---
 doc/src/sgml/protocol.sgml                    |  18 +-
 doc/src/sgml/ref/alter_subscription.sgml      |  36 +++-
 src/backend/access/transam/twophase.c         |  79 +++++++++
 src/backend/commands/subscriptioncmds.c       | 167 ++++++++++++++----
 .../libpqwalreceiver/libpqwalreceiver.c       |  22 ++-
 src/backend/replication/logical/launcher.c    |  10 +-
 src/backend/replication/logical/worker.c      |  25 +--
 src/backend/replication/slot.c                |  45 +++--
 src/backend/replication/walsender.c           |  32 ++--
 src/bin/psql/tab-complete.c                   |   2 +-
 src/include/access/twophase.h                 |   5 +
 src/include/replication/slot.h                |   3 +-
 src/include/replication/walreceiver.h         |  12 +-
 src/include/replication/worker_internal.h     |   3 +-
 src/test/regress/expected/subscription.out    |   5 +-
 src/test/regress/sql/subscription.sql         |   5 +-
 src/test/subscription/t/021_twophase.pl       |  95 +++++++++-
 17 files changed, 450 insertions(+), 114 deletions(-)

diff --git a/doc/src/sgml/protocol.sgml b/doc/src/sgml/protocol.sgml
index 1b27d0a547..79cd599692 100644
--- a/doc/src/sgml/protocol.sgml
+++ b/doc/src/sgml/protocol.sgml
@@ -2192,7 +2192,23 @@ psql "dbname=postgres replication=database" -c "IDENTIFY_SYSTEM;"
        </varlistentry>
       </variablelist>
 
-      <para>The following option is supported:</para>
+      <para>The following options are supported:</para>
+
+      <variablelist>
+       <varlistentry>
+        <term><literal>TWO_PHASE [ <replaceable class="parameter">boolean</replaceable> ]</literal></term>
+        <listitem>
+         <para>
+          If true, this logical replication slot supports decoding of two-phase
+          commit. With this option, commands related to two-phase commit such as
+          <literal>PREPARE TRANSACTION</literal>, <literal>COMMIT PREPARED</literal>
+          and <literal>ROLLBACK PREPARED</literal> are decoded and transmitted.
+          The transaction will be decoded and transmitted at
+          <literal>PREPARE TRANSACTION</literal> time.
+         </para>
+        </listitem>
+       </varlistentry>
+      </variablelist>
 
       <variablelist>
        <varlistentry>
diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index 476f195622..cbba1eeca4 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -68,8 +68,9 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
   <para>
    Commands <command>ALTER SUBSCRIPTION ... REFRESH PUBLICATION</command>,
    <command>ALTER SUBSCRIPTION ... {SET|ADD|DROP} PUBLICATION ...</command>
-   with <literal>refresh</literal> option as <literal>true</literal> and
-   <command>ALTER SUBSCRIPTION ... SET (failover = true|false)</command>
+   with <literal>refresh</literal> option as <literal>true</literal>,
+   <command>ALTER SUBSCRIPTION ... SET (failover = true|false)</command> and
+   <command>ALTER SUBSCRIPTION ... SET (two_phase = false)</command>
    cannot be executed inside a transaction block.
 
    These commands also cannot be executed when the subscription has
@@ -228,8 +229,9 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-disable-on-error"><literal>disable_on_error</literal></link>,
       <link linkend="sql-createsubscription-params-with-password-required"><literal>password_required</literal></link>,
       <link linkend="sql-createsubscription-params-with-run-as-owner"><literal>run_as_owner</literal></link>,
-      <link linkend="sql-createsubscription-params-with-origin"><literal>origin</literal></link>, and
-      <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>.
+      <link linkend="sql-createsubscription-params-with-origin"><literal>origin</literal></link>,
+      <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>, and
+      <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>.
       Only a superuser can set <literal>password_required = false</literal>.
      </para>
 
@@ -252,6 +254,32 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>
       option is enabled.
      </para>
+
+     <para>
+      The <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>
+      and <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>
+      parameters can only be altered when the subscription is disabled.
+     </para>
+
+     <para>
+      When altering <link linkend="sql-createsubscription-params-with-two-phase"><literal>two_phase</literal></link>
+      from <literal>true</literal> to <literal>false</literal>, the backend
+      process reports an error if any prepared transactions done by the
+      logical replication worker (from when <literal>two_phase</literal>
+      parameter was still <literal>true</literal>) are found. You can resolve
+      prepared transactions on the publisher node, or manually roll back them
+      on the subscriber, and then try again. The transactions prepared by
+      logical replication worker corresponding to a particular subscription have
+      the following pattern: <quote><literal>pg_gid_%u_%u</literal></quote>
+      (parameters: subscription <parameter>oid</parameter>, remote transaction id <parameter>xid</parameter>).
+      To resolve such transactions manually, one needs to roll back all
+      the prepared transactions with corresponding subscription IDs in their
+      names. Applications can check
+      <link linkend="view-pg-prepared-xacts"><structname>pg_prepared_xacts</structname></link>
+      to find the required prepared transactions. After the <literal>two_phase</literal>
+      option is changed from <literal>true</literal> to <literal>false</literal>,
+      the publisher will replicate the transactions again when they are committed.
+     </para>
     </listitem>
    </varlistentry>
 
diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index 9a8257fcaf..e98286d768 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -2681,3 +2681,82 @@ LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 	LWLockRelease(TwoPhaseStateLock);
 	return found;
 }
+
+/*
+ * TwoPhaseTransactionGid
+ *		Form the prepared transaction GID for two_phase transactions.
+ *
+ * Return the GID in the supplied buffer.
+ */
+void
+TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid_res, int szgid)
+{
+	Assert(OidIsValid(subid));
+
+	if (!TransactionIdIsValid(xid))
+		ereport(ERROR,
+				(errcode(ERRCODE_PROTOCOL_VIOLATION),
+				 errmsg_internal("invalid two-phase transaction ID")));
+
+	snprintf(gid_res, szgid, "pg_gid_%u_%u", subid, xid);
+}
+
+/*
+ * IsTwoPhaseTransactionGidForSubid
+ *		Check whether the given GID (as formed by TwoPhaseTransactionGid) is
+ *		for the specified 'subid'.
+ */
+static bool
+IsTwoPhaseTransactionGidForSubid(Oid subid, char *gid)
+{
+	int			ret;
+	Oid			subid_from_gid;
+	TransactionId xid_from_gid;
+	char		gid_tmp[GIDSIZE];
+
+	/* Extract the subid and xid from the given GID */
+	ret = sscanf(gid, "pg_gid_%u_%u", &subid_from_gid, &xid_from_gid);
+
+	/*
+	 * Check that the given GID has expected format, and at least the subid
+	 * matches.
+	 */
+	if (ret != 2 || subid != subid_from_gid)
+		return false;
+
+	/*
+	 * Reconstruct a temporary GID based on the subid and xid extracted from
+	 * the given GID and check whether the temporary GID and the given GID
+	 * match.
+	 */
+	TwoPhaseTransactionGid(subid, xid_from_gid, gid_tmp, sizeof(gid_tmp));
+
+	return strcmp(gid, gid_tmp) == 0;
+}
+
+/*
+ * LookupGXactBySubid
+ *		Check if the prepared transaction done by apply worker exists.
+ */
+bool
+LookupGXactBySubid(Oid subid)
+{
+	bool		found = false;
+
+	LWLockAcquire(TwoPhaseStateLock, LW_SHARED);
+	for (int i = 0; i < TwoPhaseState->numPrepXacts; i++)
+	{
+		GlobalTransaction gxact = TwoPhaseState->prepXacts[i];
+
+		/* Ignore not-yet-valid GIDs. */
+		if (gxact->valid &&
+			IsTwoPhaseTransactionGidForSubid(subid, gxact->gid))
+		{
+			found = true;
+			break;
+		}
+	}
+	LWLockRelease(TwoPhaseStateLock);
+
+	return found;
+}
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index 16d83b3253..27560f139a 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -16,6 +16,7 @@
 
 #include "access/htup_details.h"
 #include "access/table.h"
+#include "access/twophase.h"
 #include "access/xact.h"
 #include "catalog/catalog.h"
 #include "catalog/dependency.h"
@@ -109,6 +110,8 @@ static void check_publications_origin(WalReceiverConn *wrconn,
 static void check_duplicates_in_publist(List *publist, Datum *datums);
 static List *merge_publications(List *oldpublist, List *newpublist, bool addpub, const char *subname);
 static void ReportSlotConnectionError(List *rstates, Oid subid, char *slotname, char *err);
+static void CheckAlterSubOption(Subscription *sub, const char *option,
+								bool slot_needs_update, bool isTopLevel);
 
 
 /*
@@ -259,21 +262,9 @@ parse_subscription_options(ParseState *pstate, List *stmt_options,
 			opts->specified_opts |= SUBOPT_STREAMING;
 			opts->streaming = defGetStreamingMode(defel);
 		}
-		else if (strcmp(defel->defname, "two_phase") == 0)
+		else if (IsSet(supported_opts, SUBOPT_TWOPHASE_COMMIT) &&
+				 strcmp(defel->defname, "two_phase") == 0)
 		{
-			/*
-			 * Do not allow toggling of two_phase option. Doing so could cause
-			 * missing of transactions and lead to an inconsistent replica.
-			 * See comments atop worker.c
-			 *
-			 * Note: Unsupported twophase indicates that this call originated
-			 * from AlterSubscription.
-			 */
-			if (!IsSet(supported_opts, SUBOPT_TWOPHASE_COMMIT))
-				ereport(ERROR,
-						(errcode(ERRCODE_SYNTAX_ERROR),
-						 errmsg("unrecognized subscription parameter: \"%s\"", defel->defname)));
-
 			if (IsSet(opts->specified_opts, SUBOPT_TWOPHASE_COMMIT))
 				errorConflictingDefElem(defel, pstate);
 
@@ -1079,6 +1070,60 @@ AlterSubscription_refresh(Subscription *sub, bool copy_data,
 		table_close(rel, NoLock);
 }
 
+/*
+ * Common checks for altering failover and two_phase options.
+ */
+static void
+CheckAlterSubOption(Subscription *sub, const char *option,
+					bool slot_needs_update, bool isTopLevel)
+{
+	/*
+	 * The checks in this function are required only for failover and
+	 * two_phase options.
+	 */
+	Assert(strcmp(option, "failover") == 0 ||
+		   strcmp(option, "two_phase") == 0);
+
+	/*
+	 * Do not allow changing the option if the subscription is enabled. This
+	 * is because both failover and two_phase options of the slot on the
+	 * publisher cannot be modified if the slot is currently acquired by the
+	 * existing walsender.
+	 *
+	 * Note that the two_phase is enabled (aka changed from 'false' to 'true')
+	 * on the publisher by the existing walsender so, ideally, we can allow
+	 * that even when a subscription is enabled. But we kept this restriction
+	 * for the sake of consistency and simplicity.
+	 */
+	if (sub->enabled)
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("cannot set %s for enabled subscription",
+						option)));
+
+	if (slot_needs_update)
+	{
+		StringInfoData cmd;
+
+		/*
+		 * A valid slot must be associated with the subscription for us to
+		 * modify any of the slot's properties.
+		 */
+		if (!sub->slotname)
+			ereport(ERROR,
+					(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+					 errmsg("cannot set %s for a subscription that does not have a slot name",
+							option)));
+
+		/* The changed option of the slot can't be rolled back. */
+		initStringInfo(&cmd);
+		appendStringInfo(&cmd, "ALTER SUBSCRIPTION ... SET (%s)", option);
+
+		PreventInTransactionBlock(isTopLevel, cmd.data);
+		pfree(cmd.data);
+	}
+}
+
 /*
  * Alter the existing subscription.
  */
@@ -1094,6 +1139,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 	HeapTuple	tup;
 	Oid			subid;
 	bool		update_tuple = false;
+	bool		update_failover = false;
+	bool		update_two_phase = false;
 	Subscription *sub;
 	Form_pg_subscription form;
 	bits32		supported_opts;
@@ -1145,7 +1192,8 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 			{
 				supported_opts = (SUBOPT_SLOT_NAME |
 								  SUBOPT_SYNCHRONOUS_COMMIT | SUBOPT_BINARY |
-								  SUBOPT_STREAMING | SUBOPT_DISABLE_ON_ERR |
+								  SUBOPT_STREAMING | SUBOPT_TWOPHASE_COMMIT |
+								  SUBOPT_DISABLE_ON_ERR |
 								  SUBOPT_PASSWORD_REQUIRED |
 								  SUBOPT_RUN_AS_OWNER | SUBOPT_FAILOVER |
 								  SUBOPT_ORIGIN);
@@ -1227,31 +1275,80 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 					replaces[Anum_pg_subscription_subrunasowner - 1] = true;
 				}
 
-				if (IsSet(opts.specified_opts, SUBOPT_FAILOVER))
+				if (IsSet(opts.specified_opts, SUBOPT_TWOPHASE_COMMIT))
 				{
-					if (!sub->slotname)
+					/*
+					 * We need to update both the slot and the subscription
+					 * for two_phase option. We can enable the two_phase
+					 * option for a slot only once the initial data
+					 * syncronization is done. This is to avoid missing some
+					 * data as explained in comments atop worker.c.
+					 */
+					update_two_phase = !opts.twophase;
+
+					CheckAlterSubOption(sub, "two_phase", update_two_phase,
+										isTopLevel);
+
+					/*
+					 * Modifying the two_phase slot option requires a slot
+					 * lookup by slot name, so changing the slot name at the
+					 * same time is not allowed.
+					 */
+					if (update_two_phase &&
+						IsSet(opts.specified_opts, SUBOPT_SLOT_NAME))
+						ereport(ERROR,
+								(errcode(ERRCODE_SYNTAX_ERROR),
+								 errmsg("slot_name and two_phase cannot be altered at the same time")));
+
+					/*
+					 * Note that workers may still survive even if the
+					 * subscription has been disabled.
+					 *
+					 * Ensure workers have already been exited to avoid
+					 * getting prepared transactions while we are disabling
+					 * two_phase option. Otherwise, the changes of already
+					 * prepared transactions can be replicated again along
+					 * with its corresponding commit leading to duplicate data
+					 * or errors.
+					 */
+					if (logicalrep_workers_find(subid, true, true))
 						ereport(ERROR,
 								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-								 errmsg("cannot set %s for a subscription that does not have a slot name",
-										"failover")));
+								 errmsg("cannot alter two_phase when logical replication worker is still running"),
+								 errhint("Try again after some time.")));
 
 					/*
-					 * Do not allow changing the failover state if the
-					 * subscription is enabled. This is because the failover
-					 * state of the slot on the publisher cannot be modified
-					 * if the slot is currently acquired by the apply worker.
+					 * two_phase cannot be disabled if there are any
+					 * uncommitted prepared transactions present otherwise it
+					 * can lead to duplicate data or errors as explained in
+					 * the comment above.
 					 */
-					if (sub->enabled)
+					if (update_two_phase &&
+						sub->twophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED &&
+						LookupGXactBySubid(subid))
 						ereport(ERROR,
 								(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-								 errmsg("cannot set %s for enabled subscription",
-										"failover")));
+								 errmsg("cannot disable two_phase when prepared transactions are present"),
+								 errhint("Resolve these transactions and try again.")));
+
+					/* Change system catalog accordingly */
+					values[Anum_pg_subscription_subtwophasestate - 1] =
+						CharGetDatum(opts.twophase ?
+									 LOGICALREP_TWOPHASE_STATE_PENDING :
+									 LOGICALREP_TWOPHASE_STATE_DISABLED);
+					replaces[Anum_pg_subscription_subtwophasestate - 1] = true;
+				}
 
+				if (IsSet(opts.specified_opts, SUBOPT_FAILOVER))
+				{
 					/*
-					 * The changed failover option of the slot can't be rolled
-					 * back.
+					 * Similar to the two_phase case above, we need to update
+					 * the failover option for the slot and the subscription.
 					 */
-					PreventInTransactionBlock(isTopLevel, "ALTER SUBSCRIPTION ... SET (failover)");
+					update_failover = true;
+
+					CheckAlterSubOption(sub, "failover", update_failover,
+										isTopLevel);
 
 					values[Anum_pg_subscription_subfailover - 1] =
 						BoolGetDatum(opts.failover);
@@ -1501,13 +1598,13 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 	}
 
 	/*
-	 * Try to acquire the connection necessary for altering slot.
+	 * Try to acquire the connection necessary for altering slot, if needed.
 	 *
 	 * This has to be at the end because otherwise if there is an error while
 	 * doing the database operations we won't be able to rollback altered
 	 * slot.
 	 */
-	if (replaces[Anum_pg_subscription_subfailover - 1])
+	if (update_failover || update_two_phase)
 	{
 		bool		must_use_password;
 		char	   *err;
@@ -1528,7 +1625,9 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 
 		PG_TRY();
 		{
-			walrcv_alter_slot(wrconn, sub->slotname, opts.failover);
+			walrcv_alter_slot(wrconn, sub->slotname,
+							  update_failover ? &opts.failover : NULL,
+							  update_two_phase ? &opts.twophase : NULL);
 		}
 		PG_FINALLY();
 		{
@@ -1675,9 +1774,7 @@ DropSubscription(DropSubscriptionStmt *stmt, bool isTopLevel)
 	 * New workers won't be started because we hold an exclusive lock on the
 	 * subscription till the end of the transaction.
 	 */
-	LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
-	subworkers = logicalrep_workers_find(subid, false);
-	LWLockRelease(LogicalRepWorkerLock);
+	subworkers = logicalrep_workers_find(subid, false, true);
 	foreach(lc, subworkers)
 	{
 		LogicalRepWorker *w = (LogicalRepWorker *) lfirst(lc);
diff --git a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
index 6c42c209d2..97f957cd87 100644
--- a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
+++ b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
@@ -80,7 +80,7 @@ static char *libpqrcv_create_slot(WalReceiverConn *conn,
 								  CRSSnapshotAction snapshot_action,
 								  XLogRecPtr *lsn);
 static void libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-								bool failover);
+								const bool *failover, const bool *two_phase);
 static pid_t libpqrcv_get_backend_pid(WalReceiverConn *conn);
 static WalRcvExecResult *libpqrcv_exec(WalReceiverConn *conn,
 									   const char *query,
@@ -1121,15 +1121,27 @@ libpqrcv_create_slot(WalReceiverConn *conn, const char *slotname,
  */
 static void
 libpqrcv_alter_slot(WalReceiverConn *conn, const char *slotname,
-					bool failover)
+					const bool *failover, const bool *two_phase)
 {
 	StringInfoData cmd;
 	PGresult   *res;
 
 	initStringInfo(&cmd);
-	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( FAILOVER %s )",
-					 quote_identifier(slotname),
-					 failover ? "true" : "false");
+	appendStringInfo(&cmd, "ALTER_REPLICATION_SLOT %s ( ",
+					 quote_identifier(slotname));
+
+	if (failover)
+		appendStringInfo(&cmd, "FAILOVER %s",
+						 *failover ? "true" : "false");
+
+	if (failover && two_phase)
+		appendStringInfo(&cmd, ", ");
+
+	if (two_phase)
+		appendStringInfo(&cmd, "TWO_PHASE %s",
+						 *two_phase ? "true" : "false");
+
+	appendStringInfoString(&cmd, " );");
 
 	res = libpqrcv_PQexec(conn->streamConn, cmd.data);
 	pfree(cmd.data);
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 27c3a91fb7..c566d50a07 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -272,11 +272,14 @@ logicalrep_worker_find(Oid subid, Oid relid, bool only_running)
  * the subscription, instead of just one.
  */
 List *
-logicalrep_workers_find(Oid subid, bool only_running)
+logicalrep_workers_find(Oid subid, bool only_running, bool acquire_lock)
 {
 	int			i;
 	List	   *res = NIL;
 
+	if (acquire_lock)
+		LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
+
 	Assert(LWLockHeldByMe(LogicalRepWorkerLock));
 
 	/* Search for attached worker for a given subscription id. */
@@ -288,6 +291,9 @@ logicalrep_workers_find(Oid subid, bool only_running)
 			res = lappend(res, w);
 	}
 
+	if (acquire_lock)
+		LWLockRelease(LogicalRepWorkerLock);
+
 	return res;
 }
 
@@ -759,7 +765,7 @@ logicalrep_worker_detach(void)
 
 		LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
 
-		workers = logicalrep_workers_find(MyLogicalRepWorker->subid, true);
+		workers = logicalrep_workers_find(MyLogicalRepWorker->subid, true, false);
 		foreach(lc, workers)
 		{
 			LogicalRepWorker *w = (LogicalRepWorker *) lfirst(lc);
diff --git a/src/backend/replication/logical/worker.c b/src/backend/replication/logical/worker.c
index c0bda6269b..6c798cd5b4 100644
--- a/src/backend/replication/logical/worker.c
+++ b/src/backend/replication/logical/worker.c
@@ -401,9 +401,6 @@ static void apply_handle_tuple_routing(ApplyExecutionData *edata,
 									   LogicalRepTupleData *newtup,
 									   CmdType operation);
 
-/* Compute GID for two_phase transactions */
-static void TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid, int szgid);
-
 /* Functions for skipping changes */
 static void maybe_start_skipping_changes(XLogRecPtr finish_lsn);
 static void stop_skipping_changes(void);
@@ -3911,7 +3908,7 @@ maybe_reread_subscription(void)
 	/* !slotname should never happen when enabled is true. */
 	Assert(newsub->slotname);
 
-	/* two-phase should not be altered */
+	/* two-phase cannot be altered while the worker exists */
 	Assert(newsub->twophasestate == MySubscription->twophasestate);
 
 	/*
@@ -4396,24 +4393,6 @@ cleanup_subxact_info()
 	subxact_data.nsubxacts_max = 0;
 }
 
-/*
- * Form the prepared transaction GID for two_phase transactions.
- *
- * Return the GID in the supplied buffer.
- */
-static void
-TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid, int szgid)
-{
-	Assert(subid != InvalidRepOriginId);
-
-	if (!TransactionIdIsValid(xid))
-		ereport(ERROR,
-				(errcode(ERRCODE_PROTOCOL_VIOLATION),
-				 errmsg_internal("invalid two-phase transaction ID")));
-
-	snprintf(gid, szgid, "pg_gid_%u_%u", subid, xid);
-}
-
 /*
  * Common function to run the apply loop with error handling. Disable the
  * subscription, if necessary.
@@ -5014,7 +4993,7 @@ AtEOXact_LogicalRepWorkers(bool isCommit)
 			List	   *workers;
 			ListCell   *lc2;
 
-			workers = logicalrep_workers_find(subid, true);
+			workers = logicalrep_workers_find(subid, true, false);
 			foreach(lc2, workers)
 			{
 				LogicalRepWorker *worker = (LogicalRepWorker *) lfirst(lc2);
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index baf9b89dc4..c290339af5 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -804,9 +804,13 @@ ReplicationSlotDrop(const char *name, bool nowait)
  * Change the definition of the slot identified by the specified name.
  */
 void
-ReplicationSlotAlter(const char *name, bool failover)
+ReplicationSlotAlter(const char *name, const bool *failover,
+					 const bool *two_phase)
 {
+	bool		update_slot = false;
+
 	Assert(MyReplicationSlot == NULL);
+	Assert(failover || two_phase);
 
 	ReplicationSlotAcquire(name, false);
 
@@ -832,28 +836,45 @@ ReplicationSlotAlter(const char *name, bool failover)
 		 * Do not allow users to enable failover on the standby as we do not
 		 * support sync to the cascading standby.
 		 */
-		if (failover)
+		if (failover && *failover)
 			ereport(ERROR,
 					errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 					errmsg("cannot enable failover for a replication slot"
 						   " on the standby"));
 	}
 
-	/*
-	 * Do not allow users to enable failover for temporary slots as we do not
-	 * support syncing temporary slots to the standby.
-	 */
-	if (failover && MyReplicationSlot->data.persistency == RS_TEMPORARY)
-		ereport(ERROR,
-				errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-				errmsg("cannot enable failover for a temporary replication slot"));
+	if (failover)
+	{
+		/*
+		 * Do not allow users to enable failover for temporary slots as we do
+		 * not support syncing temporary slots to the standby.
+		 */
+		if (*failover && MyReplicationSlot->data.persistency == RS_TEMPORARY)
+			ereport(ERROR,
+					errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+					errmsg("cannot enable failover for a temporary replication slot"));
+
+		if (MyReplicationSlot->data.failover != *failover)
+		{
+			SpinLockAcquire(&MyReplicationSlot->mutex);
+			MyReplicationSlot->data.failover = *failover;
+			SpinLockRelease(&MyReplicationSlot->mutex);
+
+			update_slot = true;
+		}
+	}
 
-	if (MyReplicationSlot->data.failover != failover)
+	if (two_phase && MyReplicationSlot->data.two_phase != *two_phase)
 	{
 		SpinLockAcquire(&MyReplicationSlot->mutex);
-		MyReplicationSlot->data.failover = failover;
+		MyReplicationSlot->data.two_phase = *two_phase;
 		SpinLockRelease(&MyReplicationSlot->mutex);
 
+		update_slot = true;
+	}
+
+	if (update_slot)
+	{
 		ReplicationSlotMarkDirty();
 		ReplicationSlotSave();
 	}
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index ca205594bd..c5f1009f37 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1407,12 +1407,15 @@ DropReplicationSlot(DropReplicationSlotCmd *cmd)
 }
 
 /*
- * Process extra options given to ALTER_REPLICATION_SLOT.
+ * Change the definition of a replication slot.
  */
 static void
-ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd, bool *failover)
+AlterReplicationSlot(AlterReplicationSlotCmd *cmd)
 {
 	bool		failover_given = false;
+	bool		two_phase_given = false;
+	bool		failover;
+	bool		two_phase;
 
 	/* Parse options */
 	foreach_ptr(DefElem, defel, cmd->options)
@@ -1424,23 +1427,24 @@ ParseAlterReplSlotOptions(AlterReplicationSlotCmd *cmd, bool *failover)
 						(errcode(ERRCODE_SYNTAX_ERROR),
 						 errmsg("conflicting or redundant options")));
 			failover_given = true;
-			*failover = defGetBoolean(defel);
+			failover = defGetBoolean(defel);
+		}
+		else if (strcmp(defel->defname, "two_phase") == 0)
+		{
+			if (two_phase_given)
+				ereport(ERROR,
+						(errcode(ERRCODE_SYNTAX_ERROR),
+						 errmsg("conflicting or redundant options")));
+			two_phase_given = true;
+			two_phase = defGetBoolean(defel);
 		}
 		else
 			elog(ERROR, "unrecognized option: %s", defel->defname);
 	}
-}
-
-/*
- * Change the definition of a replication slot.
- */
-static void
-AlterReplicationSlot(AlterReplicationSlotCmd *cmd)
-{
-	bool		failover = false;
 
-	ParseAlterReplSlotOptions(cmd, &failover);
-	ReplicationSlotAlter(cmd->slotname, failover);
+	ReplicationSlotAlter(cmd->slotname,
+						 failover_given ? &failover : NULL,
+						 two_phase_given ? &two_phase : NULL);
 }
 
 /*
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
index d453e224d9..891face1b6 100644
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -1948,7 +1948,7 @@ psql_completion(const char *text, int start, int end)
 	else if (HeadMatches("ALTER", "SUBSCRIPTION", MatchAny) && TailMatches("SET", "("))
 		COMPLETE_WITH("binary", "disable_on_error", "failover", "origin",
 					  "password_required", "run_as_owner", "slot_name",
-					  "streaming", "synchronous_commit");
+					  "streaming", "synchronous_commit", "two_phase");
 	/* ALTER SUBSCRIPTION <name> SKIP ( */
 	else if (HeadMatches("ALTER", "SUBSCRIPTION", MatchAny) && TailMatches("SKIP", "("))
 		COMPLETE_WITH("lsn");
diff --git a/src/include/access/twophase.h b/src/include/access/twophase.h
index 56248c0006..b85b65c604 100644
--- a/src/include/access/twophase.h
+++ b/src/include/access/twophase.h
@@ -62,4 +62,9 @@ extern void PrepareRedoRemove(TransactionId xid, bool giveWarning);
 extern void restoreTwoPhaseData(void);
 extern bool LookupGXact(const char *gid, XLogRecPtr prepare_end_lsn,
 						TimestampTz origin_prepare_timestamp);
+
+extern void TwoPhaseTransactionGid(Oid subid, TransactionId xid, char *gid_res,
+								   int szgid);
+extern bool LookupGXactBySubid(Oid subid);
+
 #endif							/* TWOPHASE_H */
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index c9675ee87c..c2ee149fd6 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -243,7 +243,8 @@ extern void ReplicationSlotCreate(const char *name, bool db_specific,
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
 extern void ReplicationSlotDropAcquired(void);
-extern void ReplicationSlotAlter(const char *name, bool failover);
+extern void ReplicationSlotAlter(const char *name, const bool *failover,
+								 const bool *two_phase);
 
 extern void ReplicationSlotAcquire(const char *name, bool nowait);
 extern void ReplicationSlotRelease(void);
diff --git a/src/include/replication/walreceiver.h b/src/include/replication/walreceiver.h
index 12f71fa99b..7ffa5a58b3 100644
--- a/src/include/replication/walreceiver.h
+++ b/src/include/replication/walreceiver.h
@@ -372,12 +372,14 @@ typedef char *(*walrcv_create_slot_fn) (WalReceiverConn *conn,
 /*
  * walrcv_alter_slot_fn
  *
- * Change the definition of a replication slot. Currently, it only supports
- * changing the failover property of the slot.
+ * Change the definition of a replication slot. Currently, it supports
+ * changing the failover and the two_phase property of the slot.
  */
 typedef void (*walrcv_alter_slot_fn) (WalReceiverConn *conn,
 									  const char *slotname,
-									  bool failover);
+									  const bool *failover,
+									  const bool *two_phase);
+
 
 /*
  * walrcv_get_backend_pid_fn
@@ -455,8 +457,8 @@ extern PGDLLIMPORT WalReceiverFunctionsType *WalReceiverFunctions;
 	WalReceiverFunctions->walrcv_send(conn, buffer, nbytes)
 #define walrcv_create_slot(conn, slotname, temporary, two_phase, failover, snapshot_action, lsn) \
 	WalReceiverFunctions->walrcv_create_slot(conn, slotname, temporary, two_phase, failover, snapshot_action, lsn)
-#define walrcv_alter_slot(conn, slotname, failover) \
-	WalReceiverFunctions->walrcv_alter_slot(conn, slotname, failover)
+#define walrcv_alter_slot(conn, slotname, failover, two_phase) \
+	WalReceiverFunctions->walrcv_alter_slot(conn, slotname, failover, two_phase)
 #define walrcv_get_backend_pid(conn) \
 	WalReceiverFunctions->walrcv_get_backend_pid(conn)
 #define walrcv_exec(conn, exec, nRetTypes, retTypes) \
diff --git a/src/include/replication/worker_internal.h b/src/include/replication/worker_internal.h
index 515aefd519..9646261d7e 100644
--- a/src/include/replication/worker_internal.h
+++ b/src/include/replication/worker_internal.h
@@ -240,7 +240,8 @@ extern PGDLLIMPORT bool InitializingApplyWorker;
 extern void logicalrep_worker_attach(int slot);
 extern LogicalRepWorker *logicalrep_worker_find(Oid subid, Oid relid,
 												bool only_running);
-extern List *logicalrep_workers_find(Oid subid, bool only_running);
+extern List *logicalrep_workers_find(Oid subid, bool only_running,
+									 bool acquire_lock);
 extern bool logicalrep_worker_launch(LogicalRepWorkerType wtype,
 									 Oid dbid, Oid subid, const char *subname,
 									 Oid userid, Oid relid,
diff --git a/src/test/regress/expected/subscription.out b/src/test/regress/expected/subscription.out
index 5c2f1ee517..17d48b1685 100644
--- a/src/test/regress/expected/subscription.out
+++ b/src/test/regress/expected/subscription.out
@@ -377,10 +377,7 @@ HINT:  To initiate replication, you must manually create the replication slot, e
  regress_testsub | regress_subscription_user | f       | {testpub}   | f      | off       | p                | f                | any    | t                 | f             | f        | off                | dbname=regress_doesnotexist | 0/0
 (1 row)
 
---fail - alter of two_phase option not supported.
-ALTER SUBSCRIPTION regress_testsub SET (two_phase = false);
-ERROR:  unrecognized subscription parameter: "two_phase"
--- but can alter streaming when two_phase enabled
+-- we can alter streaming when two_phase enabled
 ALTER SUBSCRIPTION regress_testsub SET (streaming = true);
 \dRs+
                                                                                                                 List of subscriptions
diff --git a/src/test/regress/sql/subscription.sql b/src/test/regress/sql/subscription.sql
index 3e5ba4cb8c..007c9e7037 100644
--- a/src/test/regress/sql/subscription.sql
+++ b/src/test/regress/sql/subscription.sql
@@ -256,10 +256,7 @@ CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUB
 CREATE SUBSCRIPTION regress_testsub CONNECTION 'dbname=regress_doesnotexist' PUBLICATION testpub WITH (connect = false, two_phase = true);
 
 \dRs+
---fail - alter of two_phase option not supported.
-ALTER SUBSCRIPTION regress_testsub SET (two_phase = false);
-
--- but can alter streaming when two_phase enabled
+-- we can alter streaming when two_phase enabled
 ALTER SUBSCRIPTION regress_testsub SET (streaming = true);
 
 \dRs+
diff --git a/src/test/subscription/t/021_twophase.pl b/src/test/subscription/t/021_twophase.pl
index 9437cd4c3b..a6fbb6cf00 100644
--- a/src/test/subscription/t/021_twophase.pl
+++ b/src/test/subscription/t/021_twophase.pl
@@ -367,6 +367,99 @@ $result =
   $node_subscriber->safe_psql('postgres', "SELECT count(*) FROM tab_copy;");
 is($result, qq(2), 'replicated data in subscriber table');
 
+# Clean up
+$node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub");
+
+###############################
+# Alter the subscription to two_phase = false.
+# Verify that the altered subscription reflects the two_phase option.
+###############################
+
+# Confirm two-phase slot option is enabled before altering
+$result = $node_publisher->safe_psql('postgres',
+	"SELECT two_phase FROM pg_replication_slots WHERE slot_name = 'tap_sub_copy';"
+);
+is($result, qq(t), 'two-phase is enabled');
+
+# Alter subscription two_phase to false
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy DISABLE;");
+$node_subscriber->poll_query_until('postgres',
+	"SELECT count(*) = 0 FROM pg_stat_activity WHERE backend_type = 'logical replication worker'"
+);
+$node_subscriber->safe_psql(
+	'postgres', "
+    ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = false);
+    ALTER SUBSCRIPTION tap_sub_copy ENABLE;");
+
+# Wait for subscription startup
+$node_subscriber->wait_for_subscription_sync($node_publisher, $appname_copy);
+
+# Make sure that the two-phase is disabled on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT subtwophasestate FROM pg_subscription WHERE subname = 'tap_sub_copy';"
+);
+is($result, qq(d), 'two-phase subscription option should be disabled');
+
+# Make sure that the two-phase slot option is also disabled
+$result = $node_publisher->safe_psql('postgres',
+	"SELECT two_phase FROM pg_replication_slots WHERE slot_name = 'tap_sub_copy';"
+);
+is($result, qq(f), 'two-phase slot option should be disabled');
+
+###############################
+# Now do a prepare on the publisher and verify that it is not replicated.
+###############################
+$node_publisher->safe_psql(
+	'postgres', qq{
+    BEGIN;
+    INSERT INTO tab_copy VALUES (100);
+    PREPARE TRANSACTION 'newgid';
+	});
+
+# Wait for the subscriber to catchup
+$node_publisher->wait_for_catchup($appname_copy);
+
+# Make sure there are no prepared transactions on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT count(*) FROM pg_prepared_xacts;");
+is($result, qq(0), 'should be no prepared transactions on subscriber');
+
+###############################
+# Toggle the two_phase to "true" before the COMMIT PREPARED.
+#
+# Also, set failover to "true" to test the code path where
+# both two_phase and failover are altered at the same time.
+###############################
+$node_subscriber->safe_psql('postgres',
+	"ALTER SUBSCRIPTION tap_sub_copy DISABLE;");
+$node_subscriber->poll_query_until('postgres',
+	"SELECT count(*) = 0 FROM pg_stat_activity WHERE backend_type = 'logical replication worker'"
+);
+$node_subscriber->safe_psql(
+	'postgres', "
+    ALTER SUBSCRIPTION tap_sub_copy SET (two_phase = true, failover = true);
+    ALTER SUBSCRIPTION tap_sub_copy ENABLE;");
+
+###############################
+# Now commit the insert and verify that it is replicated.
+###############################
+$node_publisher->safe_psql('postgres', "COMMIT PREPARED 'newgid';");
+
+# Wait for the subscriber to catchup
+$node_publisher->wait_for_catchup($appname_copy);
+
+# Make sure that the committed transaction is replicated.
+$result =
+  $node_subscriber->safe_psql('postgres', "SELECT count(*) FROM tab_copy;");
+is($result, qq(3), 'replicated data in subscriber table');
+
+# Make sure that the two-phase is enabled on the subscriber
+$result = $node_subscriber->safe_psql('postgres',
+	"SELECT subtwophasestate FROM pg_subscription WHERE subname = 'tap_sub_copy';"
+);
+is($result, qq(e), 'two-phase should be enabled');
+
 $node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub_copy;");
 $node_publisher->safe_psql('postgres', "DROP PUBLICATION tap_pub_copy;");
 
@@ -374,8 +467,6 @@ $node_publisher->safe_psql('postgres', "DROP PUBLICATION tap_pub_copy;");
 # check all the cleanup
 ###############################
 
-$node_subscriber->safe_psql('postgres', "DROP SUBSCRIPTION tap_sub");
-
 $result = $node_subscriber->safe_psql('postgres',
 	"SELECT count(*) FROM pg_subscription");
 is($result, qq(0), 'check subscription was dropped on subscriber');
-- 
2.39.1

diff --git a/doc/src/sgml/ref/alter_subscription.sgml b/doc/src/sgml/ref/alter_subscription.sgml
index cbba1ee..6af6d0d 100644
--- a/doc/src/sgml/ref/alter_subscription.sgml
+++ b/doc/src/sgml/ref/alter_subscription.sgml
@@ -272,7 +272,7 @@ ALTER SUBSCRIPTION <replaceable class="parameter">name</replaceable> RENAME TO <
       logical replication worker corresponding to a particular subscription have
       the following pattern: <quote><literal>pg_gid_%u_%u</literal></quote>
       (parameters: subscription <parameter>oid</parameter>, remote transaction id <parameter>xid</parameter>).
-      To resolve such transactions manually, one needs to roll back all
+      To resolve such transactions manually, you need to roll back all
       the prepared transactions with corresponding subscription IDs in their
       names. Applications can check
       <link linkend="view-pg-prepared-xacts"><structname>pg_prepared_xacts</structname></link>
diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index 27560f1..b21f5c0 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -1090,9 +1090,9 @@ CheckAlterSubOption(Subscription *sub, const char *option,
 	 * publisher cannot be modified if the slot is currently acquired by the
 	 * existing walsender.
 	 *
-	 * Note that the two_phase is enabled (aka changed from 'false' to 'true')
-	 * on the publisher by the existing walsender so, ideally, we can allow
-	 * that even when a subscription is enabled. But we kept this restriction
+	 * Note that two_phase is enabled (aka changed from 'false' to 'true')
+	 * on the publisher by the existing walsender, so we could have allowed
+	 * that even when the subscription is enabled. But we kept this restriction
 	 * for the sake of consistency and simplicity.
 	 */
 	if (sub->enabled)
@@ -1281,7 +1281,7 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 					 * We need to update both the slot and the subscription
 					 * for two_phase option. We can enable the two_phase
 					 * option for a slot only once the initial data
-					 * syncronization is done. This is to avoid missing some
+					 * synchronization is done. This is to avoid missing some
 					 * data as explained in comments atop worker.c.
 					 */
 					update_two_phase = !opts.twophase;
@@ -1306,9 +1306,9 @@ AlterSubscription(ParseState *pstate, AlterSubscriptionStmt *stmt,
 					 *
 					 * Ensure workers have already been exited to avoid
 					 * getting prepared transactions while we are disabling
-					 * two_phase option. Otherwise, the changes of already
-					 * prepared transactions can be replicated again along
-					 * with its corresponding commit leading to duplicate data
+					 * two_phase option. Otherwise, the changes of an already
+					 * prepared transaction can be replicated again along
+					 * with its corresponding commit, leading to duplicate data
 					 * or errors.
 					 */
 					if (logicalrep_workers_find(subid, true, true))