Move replication slot structures/enums/macros to a new header file for better usability by external tools/modules

From 087de72a5aa9cb8c53729d4c15ea0f481fbc97a2 Mon Sep 17 00:00:00 2001
From: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>
Date: Thu, 10 Feb 2022 04:18:53 +0000
Subject: [PATCH v2] Add new header file for replication slot common data
 structures

This makes the external tools/modules to use the replication
slot data structures.
---
 src/backend/replication/slot.c        |  39 --------
 src/include/replication/repl_common.h | 138 ++++++++++++++++++++++++++
 src/include/replication/slot.h        |  82 +--------------
 3 files changed, 139 insertions(+), 120 deletions(-)
 create mode 100644 src/include/replication/repl_common.h

diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index e5e0cf8768..42dc297a03 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -50,45 +50,6 @@
 #include "storage/procarray.h"
 #include "utils/builtins.h"
 
-/*
- * Replication slot on-disk data structure.
- */
-typedef struct ReplicationSlotOnDisk
-{
-	/* first part of this struct needs to be version independent */
-
-	/* data not covered by checksum */
-	uint32		magic;
-	pg_crc32c	checksum;
-
-	/* data covered by checksum */
-	uint32		version;
-	uint32		length;
-
-	/*
-	 * The actual data in the slot that follows can differ based on the above
-	 * 'version'.
-	 */
-
-	ReplicationSlotPersistentData slotdata;
-} ReplicationSlotOnDisk;
-
-/* size of version independent data */
-#define ReplicationSlotOnDiskConstantSize \
-	offsetof(ReplicationSlotOnDisk, slotdata)
-/* size of the part of the slot not covered by the checksum */
-#define ReplicationSlotOnDiskNotChecksummedSize  \
-	offsetof(ReplicationSlotOnDisk, version)
-/* size of the part covered by the checksum */
-#define ReplicationSlotOnDiskChecksummedSize \
-	sizeof(ReplicationSlotOnDisk) - ReplicationSlotOnDiskNotChecksummedSize
-/* size of the slot data that is version dependent */
-#define ReplicationSlotOnDiskV2Size \
-	sizeof(ReplicationSlotOnDisk) - ReplicationSlotOnDiskConstantSize
-
-#define SLOT_MAGIC		0x1051CA1	/* format identifier */
-#define SLOT_VERSION	2		/* version for new files */
-
 /* Control array for replication slot management */
 ReplicationSlotCtlData *ReplicationSlotCtl = NULL;
 
diff --git a/src/include/replication/repl_common.h b/src/include/replication/repl_common.h
new file mode 100644
index 0000000000..b59a70811a
--- /dev/null
+++ b/src/include/replication/repl_common.h
@@ -0,0 +1,138 @@
+/*-------------------------------------------------------------------------
+ * repl_common.h
+ *
+ * This header file is meant to hold replication data structures and
+ * functions usable across the entire Postgres modules i.e. core, tools,
+ * and contrib modules.
+ *
+ * Copyright (c) 2022, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *    src/include/replication/repl_common.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef REPL_COMMON_H
+#define REPL_COMMON_H
+
+/*
+ * Behaviour of replication slots, upon release or crash.
+ *
+ * Slots marked as PERSISTENT are crash-safe and will not be dropped when
+ * released. Slots marked as EPHEMERAL will be dropped when released or after
+ * restarts.  Slots marked TEMPORARY will be dropped at the end of a session
+ * or on error.
+ *
+ * EPHEMERAL is used as a not-quite-ready state when creating persistent
+ * slots.  EPHEMERAL slots can be made PERSISTENT by calling
+ * ReplicationSlotPersist().  For a slot that goes away at the end of a
+ * session, TEMPORARY is the appropriate choice.
+ */
+typedef enum ReplicationSlotPersistency
+{
+	RS_PERSISTENT,
+	RS_EPHEMERAL,
+	RS_TEMPORARY
+} ReplicationSlotPersistency;
+
+/*
+ * On-Disk data of a replication slot, preserved across restarts.
+ */
+typedef struct ReplicationSlotPersistentData
+{
+	/* The slot's identifier */
+	NameData	name;
+
+	/* database the slot is active on */
+	Oid			database;
+
+	/*
+	 * The slot's behaviour when being dropped (or restored after a crash).
+	 */
+	ReplicationSlotPersistency persistency;
+
+	/*
+	 * xmin horizon for data
+	 *
+	 * NB: This may represent a value that hasn't been written to disk yet;
+	 * see notes for effective_xmin, below.
+	 */
+	TransactionId xmin;
+
+	/*
+	 * xmin horizon for catalog tuples
+	 *
+	 * NB: This may represent a value that hasn't been written to disk yet;
+	 * see notes for effective_xmin, below.
+	 */
+	TransactionId catalog_xmin;
+
+	/* oldest LSN that might be required by this replication slot */
+	XLogRecPtr	restart_lsn;
+
+	/* restart_lsn is copied here when the slot is invalidated */
+	XLogRecPtr	invalidated_at;
+
+	/*
+	 * Oldest LSN that the client has acked receipt for.  This is used as the
+	 * start_lsn point in case the client doesn't specify one, and also as a
+	 * safety measure to jump forwards in case the client specifies a
+	 * start_lsn that's further in the past than this value.
+	 */
+	XLogRecPtr	confirmed_flush;
+
+	/*
+	 * LSN at which we enabled two_phase commit for this slot or LSN at which
+	 * we found a consistent point at the time of slot creation.
+	 */
+	XLogRecPtr	two_phase_at;
+
+	/*
+	 * Allow decoding of prepared transactions?
+	 */
+	bool		two_phase;
+
+	/* plugin name */
+	NameData	plugin;
+} ReplicationSlotPersistentData;
+
+/*
+ * Replication slot on-disk data structure.
+ */
+typedef struct ReplicationSlotOnDisk
+{
+	/* first part of this struct needs to be version independent */
+
+	/* data not covered by checksum */
+	uint32		magic;
+	pg_crc32c	checksum;
+
+	/* data covered by checksum */
+	uint32		version;
+	uint32		length;
+
+	/*
+	 * The actual data in the slot that follows can differ based on the above
+	 * 'version'.
+	 */
+
+	ReplicationSlotPersistentData slotdata;
+} ReplicationSlotOnDisk;
+
+/* size of version independent data */
+#define ReplicationSlotOnDiskConstantSize \
+	offsetof(ReplicationSlotOnDisk, slotdata)
+/* size of the part of the slot not covered by the checksum */
+#define ReplicationSlotOnDiskNotChecksummedSize \
+	offsetof(ReplicationSlotOnDisk, version)
+/* size of the part covered by the checksum */
+#define ReplicationSlotOnDiskChecksummedSize \
+	sizeof(ReplicationSlotOnDisk) - ReplicationSlotOnDiskNotChecksummedSize
+/* size of the slot data that is version dependent */
+#define ReplicationSlotOnDiskV2Size \
+	sizeof(ReplicationSlotOnDisk) - ReplicationSlotOnDiskConstantSize
+
+#define SLOT_MAGIC		0x1051CA1	/* format identifier */
+#define SLOT_VERSION	2		/* version for new files */
+
+#endif							/* REPL_COMMON_H */
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index f833b1d6dc..183cb025b8 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -15,89 +15,9 @@
 #include "storage/lwlock.h"
 #include "storage/shmem.h"
 #include "storage/spin.h"
+#include "replication/repl_common.h"
 #include "replication/walreceiver.h"
 
-/*
- * Behaviour of replication slots, upon release or crash.
- *
- * Slots marked as PERSISTENT are crash-safe and will not be dropped when
- * released. Slots marked as EPHEMERAL will be dropped when released or after
- * restarts.  Slots marked TEMPORARY will be dropped at the end of a session
- * or on error.
- *
- * EPHEMERAL is used as a not-quite-ready state when creating persistent
- * slots.  EPHEMERAL slots can be made PERSISTENT by calling
- * ReplicationSlotPersist().  For a slot that goes away at the end of a
- * session, TEMPORARY is the appropriate choice.
- */
-typedef enum ReplicationSlotPersistency
-{
-	RS_PERSISTENT,
-	RS_EPHEMERAL,
-	RS_TEMPORARY
-} ReplicationSlotPersistency;
-
-/*
- * On-Disk data of a replication slot, preserved across restarts.
- */
-typedef struct ReplicationSlotPersistentData
-{
-	/* The slot's identifier */
-	NameData	name;
-
-	/* database the slot is active on */
-	Oid			database;
-
-	/*
-	 * The slot's behaviour when being dropped (or restored after a crash).
-	 */
-	ReplicationSlotPersistency persistency;
-
-	/*
-	 * xmin horizon for data
-	 *
-	 * NB: This may represent a value that hasn't been written to disk yet;
-	 * see notes for effective_xmin, below.
-	 */
-	TransactionId xmin;
-
-	/*
-	 * xmin horizon for catalog tuples
-	 *
-	 * NB: This may represent a value that hasn't been written to disk yet;
-	 * see notes for effective_xmin, below.
-	 */
-	TransactionId catalog_xmin;
-
-	/* oldest LSN that might be required by this replication slot */
-	XLogRecPtr	restart_lsn;
-
-	/* restart_lsn is copied here when the slot is invalidated */
-	XLogRecPtr	invalidated_at;
-
-	/*
-	 * Oldest LSN that the client has acked receipt for.  This is used as the
-	 * start_lsn point in case the client doesn't specify one, and also as a
-	 * safety measure to jump forwards in case the client specifies a
-	 * start_lsn that's further in the past than this value.
-	 */
-	XLogRecPtr	confirmed_flush;
-
-	/*
-	 * LSN at which we enabled two_phase commit for this slot or LSN at which
-	 * we found a consistent point at the time of slot creation.
-	 */
-	XLogRecPtr	two_phase_at;
-
-	/*
-	 * Allow decoding of prepared transactions?
-	 */
-	bool		two_phase;
-
-	/* plugin name */
-	NameData	plugin;
-} ReplicationSlotPersistentData;
-
 /*
  * Shared memory state of a single replication slot.
  *
-- 
2.25.1