Log a warning in pg_createsubscriber for max_slot_wal_keep_size

From afc12bc405bdb008bacbfb8d81dc2d7533232b65 Mon Sep 17 00:00:00 2001
From: Khanna <Shubham.Khanna@fujitsu.com>
Date: Tue, 24 Dec 2024 12:27:27 +0530
Subject: [PATCH v2] Validate-max_slot_wal_keep_size-in-pg_createsubscriber

This patch introduces validation for the 'max_slot_wal_keep_size' GUC in the
'pg_createsubscriber' utility. The utility now checks that the publisher's
'max_slot_wal_keep_size' is set to '-1' during subscription creation.
This ensures proper functioning of logical replication slots.

This patch updates 'pg_createsubscriber' to fetch and validate the
'max_slot_wal_keep_size' setting from the publisher.
The test case is added to validate correct warning reporting when
'max_slot_wal_keep_size' is misconfigured.

These changes ensures that logical replication does not fail due to improper
configuration of 'max_slot_wal_keep_size' on the publisher.
---
 src/bin/pg_basebackup/pg_createsubscriber.c      | 16 +++++++++++++++-
 .../pg_basebackup/t/040_pg_createsubscriber.pl   | 16 ++++++++++++++--
 2 files changed, 29 insertions(+), 3 deletions(-)

diff --git a/src/bin/pg_basebackup/pg_createsubscriber.c b/src/bin/pg_basebackup/pg_createsubscriber.c
index e96370a9ec..34d88900b4 100644
--- a/src/bin/pg_basebackup/pg_createsubscriber.c
+++ b/src/bin/pg_basebackup/pg_createsubscriber.c
@@ -849,6 +849,7 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 	int			max_walsenders;
 	int			cur_walsenders;
 	int			max_prepared_transactions;
+	int			max_slot_wal_keep_size;
 
 	pg_log_info("checking settings on publisher");
 
@@ -880,7 +881,8 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 				 " (SELECT count(*) FROM pg_catalog.pg_replication_slots),"
 				 " pg_catalog.current_setting('max_wal_senders'),"
 				 " (SELECT count(*) FROM pg_catalog.pg_stat_activity WHERE backend_type = 'walsender'),"
-				 " pg_catalog.current_setting('max_prepared_transactions')");
+				 " pg_catalog.current_setting('max_prepared_transactions'),"
+				 " pg_catalog.current_setting('max_slot_wal_keep_size')");
 
 	if (PQresultStatus(res) != PGRES_TUPLES_OK)
 	{
@@ -895,6 +897,7 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 	max_walsenders = atoi(PQgetvalue(res, 0, 3));
 	cur_walsenders = atoi(PQgetvalue(res, 0, 4));
 	max_prepared_transactions = atoi(PQgetvalue(res, 0, 5));
+	max_slot_wal_keep_size = atoi(PQgetvalue(res, 0, 6));
 
 	PQclear(res);
 
@@ -905,6 +908,8 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 	pg_log_debug("publisher: current wal senders: %d", cur_walsenders);
 	pg_log_debug("publisher: max_prepared_transactions: %d",
 				 max_prepared_transactions);
+	pg_log_debug("publisher: max_slot_wal_keep_size: %d",
+				 max_slot_wal_keep_size);
 
 	disconnect_database(conn, false);
 
@@ -939,6 +944,15 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 							  "Prepared transactions will be replicated at COMMIT PREPARED.");
 	}
 
+	/* Validate max_slot_wal_keep_size */
+	if (dry_run && max_slot_wal_keep_size != -1)
+	{
+		pg_log_warning("publisher requires max_slot_wal_keep_size to be -1, but is set to %d",
+					   max_slot_wal_keep_size);
+		pg_log_warning_detail("Change the configuration parameter \"%s\" on the publisher to %d.",
+							  "max_slot_wal_keep_size", -1);
+	}
+
 	pg_free(wal_level);
 
 	if (failed)
diff --git a/src/bin/pg_basebackup/t/040_pg_createsubscriber.pl b/src/bin/pg_basebackup/t/040_pg_createsubscriber.pl
index 0a900edb65..daa2c8b25b 100644
--- a/src/bin/pg_basebackup/t/040_pg_createsubscriber.pl
+++ b/src/bin/pg_basebackup/t/040_pg_createsubscriber.pl
@@ -318,8 +318,13 @@ $node_p->safe_psql($db1,
 $node_p->wait_for_replay_catchup($node_s);
 $node_s->stop;
 
+# Configure 'max_slot_wal_keep_size = 1' on the publisher and verify the
+# warning message
+$node_p->append_conf('postgresql.conf', 'max_slot_wal_keep_size = 1');
+$node_p->restart;
+
 # dry run mode on node S
-command_ok(
+command_checks_all(
 	[
 		'pg_createsubscriber', '--verbose',
 		'--recovery-timeout', "$PostgreSQL::Test::Utils::timeout_default",
@@ -335,7 +340,14 @@ command_ok(
 		$db1, '--database',
 		$db2
 	],
-	'run pg_createsubscriber --dry-run on node S');
+	0,
+	[qr/./],
+	[
+		qr/pg_createsubscriber: warning: publisher requires max_slot_wal_keep_size to be -1/,
+		qr/Change the configuration parameter "max_slot_wal_keep_size" on the publisher to -1./,
+	],
+	'Validate warning for misconfigured max_slot_wal_keep_size on the publisher'
+);
 
 # Check if node S is still a standby
 $node_s->start;
-- 
2.34.1

From 0be6949498ec53011a6e62733e31a42dc2a754d8 Mon Sep 17 00:00:00 2001
From: Khanna <Shubham.Khanna@fujitsu.com>
Date: Tue, 24 Dec 2024 12:27:27 +0530
Subject: [PATCH v3] Validate-max_slot_wal_keep_size-in-pg_createsubscriber

This patch introduces validation for the 'max_slot_wal_keep_size' GUC in the
'pg_createsubscriber' utility. The utility now checks that the publisher's
'max_slot_wal_keep_size' is set to '-1' during subscription creation.
This ensures proper functioning of logical replication slots.

The 'pg_createsubscriber' utility is updated to fetch and validate the
'max_slot_wal_keep_size' setting from the publisher. A warning is raised during
the '--dry-run' mode if the configuration is set to a non-default value.

By ensuring 'max_slot_wal_keep_size' is -1, this patch prevents the potential
deletion of required WAL files on the publisher that could disrupt logical
replication. A test case has been added to validate correct warning reporting
when 'max_slot_wal_keep_size' is misconfigured.

These changes ensure that logical replication does not fail due to improper
configuration of 'max_slot_wal_keep_size' on the publisher.
---
 src/bin/pg_basebackup/pg_createsubscriber.c   | 23 ++++++++++++++++++-
 .../t/040_pg_createsubscriber.pl              | 23 ++++++++++++++++---
 2 files changed, 42 insertions(+), 4 deletions(-)

diff --git a/src/bin/pg_basebackup/pg_createsubscriber.c b/src/bin/pg_basebackup/pg_createsubscriber.c
index e96370a9ec..057ffc64eb 100644
--- a/src/bin/pg_basebackup/pg_createsubscriber.c
+++ b/src/bin/pg_basebackup/pg_createsubscriber.c
@@ -849,6 +849,7 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 	int			max_walsenders;
 	int			cur_walsenders;
 	int			max_prepared_transactions;
+	int			max_slot_wal_keep_size;
 
 	pg_log_info("checking settings on publisher");
 
@@ -880,7 +881,8 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 				 " (SELECT count(*) FROM pg_catalog.pg_replication_slots),"
 				 " pg_catalog.current_setting('max_wal_senders'),"
 				 " (SELECT count(*) FROM pg_catalog.pg_stat_activity WHERE backend_type = 'walsender'),"
-				 " pg_catalog.current_setting('max_prepared_transactions')");
+				 " pg_catalog.current_setting('max_prepared_transactions'),"
+				 " pg_catalog.current_setting('max_slot_wal_keep_size')");
 
 	if (PQresultStatus(res) != PGRES_TUPLES_OK)
 	{
@@ -895,6 +897,7 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 	max_walsenders = atoi(PQgetvalue(res, 0, 3));
 	cur_walsenders = atoi(PQgetvalue(res, 0, 4));
 	max_prepared_transactions = atoi(PQgetvalue(res, 0, 5));
+	max_slot_wal_keep_size = atoi(PQgetvalue(res, 0, 6));
 
 	PQclear(res);
 
@@ -905,6 +908,8 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 	pg_log_debug("publisher: current wal senders: %d", cur_walsenders);
 	pg_log_debug("publisher: max_prepared_transactions: %d",
 				 max_prepared_transactions);
+	pg_log_debug("publisher: max_slot_wal_keep_size: %d",
+				 max_slot_wal_keep_size);
 
 	disconnect_database(conn, false);
 
@@ -939,6 +944,22 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 							  "Prepared transactions will be replicated at COMMIT PREPARED.");
 	}
 
+/*
+ * Validate max_slot_wal_keep_size
+ * Logical replication requires max_slot_wal_keep_size to be set to -1 on the
+ * publisher to prevent the deletion of WAL files that are still needed by
+ * replication slots. If this parameter is set to a non-default value, it may
+ * cause replication failures due to required WAL files being
+ * prematurely removed.
+ */
+	if (dry_run && max_slot_wal_keep_size != -1)
+	{
+		pg_log_warning("publisher requires max_slot_wal_keep_size to be -1, but is set to %d",
+					   max_slot_wal_keep_size);
+		pg_log_warning_detail("Change the configuration parameter \"%s\" on the publisher to %d.",
+							  "max_slot_wal_keep_size", -1);
+	}
+
 	pg_free(wal_level);
 
 	if (failed)
diff --git a/src/bin/pg_basebackup/t/040_pg_createsubscriber.pl b/src/bin/pg_basebackup/t/040_pg_createsubscriber.pl
index 0a900edb65..9f57ceb085 100644
--- a/src/bin/pg_basebackup/t/040_pg_createsubscriber.pl
+++ b/src/bin/pg_basebackup/t/040_pg_createsubscriber.pl
@@ -318,8 +318,14 @@ $node_p->safe_psql($db1,
 $node_p->wait_for_replay_catchup($node_s);
 $node_s->stop;
 
-# dry run mode on node S
-command_ok(
+# Configure 'max_slot_wal_keep_size = 1' on the publisher and
+# reload configuration
+$node_p->append_conf('postgresql.conf', 'max_slot_wal_keep_size = 1');
+$node_p->reload;
+
+# dry run mode on node S and verify the warning message for misconfigured
+# 'max_slot_wal_keep_size'
+command_checks_all(
 	[
 		'pg_createsubscriber', '--verbose',
 		'--recovery-timeout', "$PostgreSQL::Test::Utils::timeout_default",
@@ -335,7 +341,18 @@ command_ok(
 		$db1, '--database',
 		$db2
 	],
-	'run pg_createsubscriber --dry-run on node S');
+	0,
+	[qr/./],
+	[
+		qr/pg_createsubscriber: warning: publisher requires max_slot_wal_keep_size to be -1/,
+		qr/Change the configuration parameter "max_slot_wal_keep_size" on the publisher to -1./,
+	],
+	'Validate warning for misconfigured max_slot_wal_keep_size on the publisher'
+);
+
+# Reset 'max_slot_wal_keep_size' to default after the test
+$node_p->append_conf('postgresql.conf', 'max_slot_wal_keep_size = -1');
+$node_p->reload;
 
 # Check if node S is still a standby
 $node_s->start;
-- 
2.41.0.windows.3

From 3641c20b2f5fec59642bb8515cf017f8188c8058 Mon Sep 17 00:00:00 2001
From: Khanna <Shubham.Khanna@fujitsu.com>
Date: Tue, 24 Dec 2024 12:27:27 +0530
Subject: [PATCH v4] Validate-max_slot_wal_keep_size-in-pg_createsubscriber

This patch introduces validation for the 'max_slot_wal_keep_size' GUC in the
'pg_createsubscriber' utility. The utility now checks that the publisher's
'max_slot_wal_keep_size' is set to '-1' during subscription creation.
This ensures proper functioning of logical replication slots.

The 'pg_createsubscriber' utility is updated to fetch and validate the
'max_slot_wal_keep_size' setting from the publisher. A warning is raised during
the '--dry-run' mode if the configuration is set to a non-default value.

By ensuring 'max_slot_wal_keep_size' is -1, this patch prevents the potential
deletion of required WAL files on the publisher that could disrupt logical
replication. A test case has been added to validate correct warning reporting
when 'max_slot_wal_keep_size' is misconfigured.
---
 doc/src/sgml/ref/pg_createsubscriber.sgml     |  7 ++++++
 src/bin/pg_basebackup/pg_createsubscriber.c   | 25 ++++++++++++++++++-
 .../t/040_pg_createsubscriber.pl              | 23 ++++++++++++++---
 3 files changed, 51 insertions(+), 4 deletions(-)

diff --git a/doc/src/sgml/ref/pg_createsubscriber.sgml b/doc/src/sgml/ref/pg_createsubscriber.sgml
index 26b8e64a4e..59bc97728e 100644
--- a/doc/src/sgml/ref/pg_createsubscriber.sgml
+++ b/doc/src/sgml/ref/pg_createsubscriber.sgml
@@ -313,6 +313,13 @@ PostgreSQL documentation
     linkend="guc-max-wal-senders"/> configured to a value greater than or equal
     to the number of specified databases and existing WAL sender processes.
    </para>
+
+   <para>
+    The 'max_slot_wal_keep_size' must be set to -1 to prevent the automatic
+    removal of WAL files needed by replication slots. Setting this parameter to
+    a specific size may lead to replication failures if required WAL files are
+    prematurely deleted.
+   </para>
   </refsect2>
 
   <refsect2>
diff --git a/src/bin/pg_basebackup/pg_createsubscriber.c b/src/bin/pg_basebackup/pg_createsubscriber.c
index e96370a9ec..3703dae33a 100644
--- a/src/bin/pg_basebackup/pg_createsubscriber.c
+++ b/src/bin/pg_basebackup/pg_createsubscriber.c
@@ -849,6 +849,7 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 	int			max_walsenders;
 	int			cur_walsenders;
 	int			max_prepared_transactions;
+	int			max_slot_wal_keep_size;
 
 	pg_log_info("checking settings on publisher");
 
@@ -872,6 +873,7 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 	 * - wal_level = logical
 	 * - max_replication_slots >= current + number of dbs to be converted
 	 * - max_wal_senders >= current + number of dbs to be converted
+	 * - max_slot_wal_keep_size = -1 (to prevent deletion of required WAL files)
 	 * -----------------------------------------------------------------------
 	 */
 	res = PQexec(conn,
@@ -880,7 +882,8 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 				 " (SELECT count(*) FROM pg_catalog.pg_replication_slots),"
 				 " pg_catalog.current_setting('max_wal_senders'),"
 				 " (SELECT count(*) FROM pg_catalog.pg_stat_activity WHERE backend_type = 'walsender'),"
-				 " pg_catalog.current_setting('max_prepared_transactions')");
+				 " pg_catalog.current_setting('max_prepared_transactions'),"
+				 " pg_catalog.current_setting('max_slot_wal_keep_size')");
 
 	if (PQresultStatus(res) != PGRES_TUPLES_OK)
 	{
@@ -895,6 +898,7 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 	max_walsenders = atoi(PQgetvalue(res, 0, 3));
 	cur_walsenders = atoi(PQgetvalue(res, 0, 4));
 	max_prepared_transactions = atoi(PQgetvalue(res, 0, 5));
+	max_slot_wal_keep_size = atoi(PQgetvalue(res, 0, 6));
 
 	PQclear(res);
 
@@ -905,6 +909,8 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 	pg_log_debug("publisher: current wal senders: %d", cur_walsenders);
 	pg_log_debug("publisher: max_prepared_transactions: %d",
 				 max_prepared_transactions);
+	pg_log_debug("publisher: max_slot_wal_keep_size: %d",
+				 max_slot_wal_keep_size);
 
 	disconnect_database(conn, false);
 
@@ -939,6 +945,23 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 							  "Prepared transactions will be replicated at COMMIT PREPARED.");
 	}
 
+/*
+ * Validate max_slot_wal_keep_size
+ * Logical replication requires max_slot_wal_keep_size to be set to -1 on the
+ * publisher to prevent the deletion of WAL files that are still needed by
+ * replication slots. If this parameter is set to a non-default value, it may
+ * cause replication failures due to required WAL files being prematurely
+ * removed.
+ */
+	if (dry_run && max_slot_wal_keep_size != -1)
+	{
+		pg_log_error("publisher requires max_slot_wal_keep_size to be -1, but only %d remain",
+					 max_slot_wal_keep_size);
+		pg_log_error_hint("Change the configuration parameter \"%s\" on the publisher to %d.",
+						  "max_slot_wal_keep_size", -1);
+		failed = true;
+	}
+
 	pg_free(wal_level);
 
 	if (failed)
diff --git a/src/bin/pg_basebackup/t/040_pg_createsubscriber.pl b/src/bin/pg_basebackup/t/040_pg_createsubscriber.pl
index 0a900edb65..f4c1e079b1 100644
--- a/src/bin/pg_basebackup/t/040_pg_createsubscriber.pl
+++ b/src/bin/pg_basebackup/t/040_pg_createsubscriber.pl
@@ -318,8 +318,14 @@ $node_p->safe_psql($db1,
 $node_p->wait_for_replay_catchup($node_s);
 $node_s->stop;
 
-# dry run mode on node S
-command_ok(
+# Configure 'max_slot_wal_keep_size = 1' on the publisher and
+# reload configuration
+$node_p->append_conf('postgresql.conf', 'max_slot_wal_keep_size = 1');
+$node_p->reload;
+
+# dry run mode on node S and verify the error message for misconfigured
+# 'max_slot_wal_keep_size'
+command_checks_all(
 	[
 		'pg_createsubscriber', '--verbose',
 		'--recovery-timeout', "$PostgreSQL::Test::Utils::timeout_default",
@@ -335,7 +341,18 @@ command_ok(
 		$db1, '--database',
 		$db2
 	],
-	'run pg_createsubscriber --dry-run on node S');
+	1,
+	[qr/./],
+	[
+		qr/pg_createsubscriber: error: publisher requires max_slot_wal_keep_size to be -1/,
+		qr/Change the configuration parameter "max_slot_wal_keep_size" on the publisher to -1./,
+	],
+	'Validate error for misconfigured max_slot_wal_keep_size on the publisher'
+);
+
+# Reset 'max_slot_wal_keep_size' to default after the test
+$node_p->append_conf('postgresql.conf', 'max_slot_wal_keep_size = -1');
+$node_p->reload;
 
 # Check if node S is still a standby
 $node_s->start;
-- 
2.41.0.windows.3

From 2490ae21e675188f54ebcb99eba1c3b4d1a09caf Mon Sep 17 00:00:00 2001
From: Khanna <Shubham.Khanna@fujitsu.com>
Date: Tue, 24 Dec 2024 12:27:27 +0530
Subject: [PATCH v5] Validate-max_slot_wal_keep_size-in-pg_createsubscriber

This patch introduces validation for the 'max_slot_wal_keep_size' GUC in the
'pg_createsubscriber' utility. The utility now checks that the publisher's
'max_slot_wal_keep_size' is set to '-1' during subscription creation.
This ensures proper functioning of logical replication slots.

The 'pg_createsubscriber' utility is updated to fetch and validate the
'max_slot_wal_keep_size' setting from the publisher. A warning is raised during
the '--dry-run' mode if the configuration is set to a non-default value.

By ensuring 'max_slot_wal_keep_size' is -1, this patch prevents the potential
deletion of required WAL files on the publisher that could disrupt logical
replication. A test case has been added to validate correct warning reporting
when 'max_slot_wal_keep_size' is misconfigured.
---
 doc/src/sgml/ref/pg_createsubscriber.sgml     |  8 +++++++
 src/bin/pg_basebackup/pg_createsubscriber.c   | 20 +++++++++++++++-
 .../t/040_pg_createsubscriber.pl              | 24 ++++++++++++++++---
 3 files changed, 48 insertions(+), 4 deletions(-)

diff --git a/doc/src/sgml/ref/pg_createsubscriber.sgml b/doc/src/sgml/ref/pg_createsubscriber.sgml
index 26b8e64a4e..27e3b6b734 100644
--- a/doc/src/sgml/ref/pg_createsubscriber.sgml
+++ b/doc/src/sgml/ref/pg_createsubscriber.sgml
@@ -313,6 +313,14 @@ PostgreSQL documentation
     linkend="guc-max-wal-senders"/> configured to a value greater than or equal
     to the number of specified databases and existing WAL sender processes.
    </para>
+
+   <para>
+    The source server must have <xref linkend="guc-max-slot-wal-keep-size"/> to
+    be set to <literal>-1</literal> to prevent the automatic removal of WAL
+    replication slots. Setting this parameter to files needed by a specific size
+    may lead to replication failures if required WAL files are
+    prematurely deleted.
+   </para>
   </refsect2>
 
   <refsect2>
diff --git a/src/bin/pg_basebackup/pg_createsubscriber.c b/src/bin/pg_basebackup/pg_createsubscriber.c
index faf18ccf13..a2ef374db5 100644
--- a/src/bin/pg_basebackup/pg_createsubscriber.c
+++ b/src/bin/pg_basebackup/pg_createsubscriber.c
@@ -849,6 +849,7 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 	int			max_walsenders;
 	int			cur_walsenders;
 	int			max_prepared_transactions;
+	int			max_slot_wal_keep_size;
 
 	pg_log_info("checking settings on publisher");
 
@@ -872,6 +873,7 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 	 * - wal_level = logical
 	 * - max_replication_slots >= current + number of dbs to be converted
 	 * - max_wal_senders >= current + number of dbs to be converted
+	 * - max_slot_wal_keep_size = -1 (to prevent deletion of required WAL files)
 	 * -----------------------------------------------------------------------
 	 */
 	res = PQexec(conn,
@@ -880,7 +882,8 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 				 " (SELECT count(*) FROM pg_catalog.pg_replication_slots),"
 				 " pg_catalog.current_setting('max_wal_senders'),"
 				 " (SELECT count(*) FROM pg_catalog.pg_stat_activity WHERE backend_type = 'walsender'),"
-				 " pg_catalog.current_setting('max_prepared_transactions')");
+				 " pg_catalog.current_setting('max_prepared_transactions'),"
+				 " pg_catalog.current_setting('max_slot_wal_keep_size')");
 
 	if (PQresultStatus(res) != PGRES_TUPLES_OK)
 	{
@@ -895,6 +898,7 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 	max_walsenders = atoi(PQgetvalue(res, 0, 3));
 	cur_walsenders = atoi(PQgetvalue(res, 0, 4));
 	max_prepared_transactions = atoi(PQgetvalue(res, 0, 5));
+	max_slot_wal_keep_size = atoi(PQgetvalue(res, 0, 6));
 
 	PQclear(res);
 
@@ -905,6 +909,8 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 	pg_log_debug("publisher: current wal senders: %d", cur_walsenders);
 	pg_log_debug("publisher: max_prepared_transactions: %d",
 				 max_prepared_transactions);
+	pg_log_debug("publisher: max_slot_wal_keep_size: %d",
+				 max_slot_wal_keep_size);
 
 	disconnect_database(conn, false);
 
@@ -939,6 +945,18 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 							  "Prepared transactions will be replicated at COMMIT PREPARED.");
 	}
 
+	/*
+	 * Validate 'max_slot_wal_keep_size'. If this parameter is set to a
+	 * non-default value, it may cause replication failures due to required
+	 * WAL files being prematurely removed.
+	 */
+	if (dry_run && max_slot_wal_keep_size != -1)
+	{
+		pg_log_warning("publisher requires WAL size must not be restricted");
+		pg_log_warning_detail("The max_slot_wal_keep_size parameter is currently set to a non-default value, which may lead to replication failures. "
+							  "This parameter must be set to -1 to ensure that required WAL files are not prematurely removed.");
+	}
+
 	pg_free(wal_level);
 
 	if (failed)
diff --git a/src/bin/pg_basebackup/t/040_pg_createsubscriber.pl b/src/bin/pg_basebackup/t/040_pg_createsubscriber.pl
index 5426159fa5..6896d3fcbf 100644
--- a/src/bin/pg_basebackup/t/040_pg_createsubscriber.pl
+++ b/src/bin/pg_basebackup/t/040_pg_createsubscriber.pl
@@ -318,8 +318,14 @@ $node_p->safe_psql($db1,
 $node_p->wait_for_replay_catchup($node_s);
 $node_s->stop;
 
-# dry run mode on node S
-command_ok(
+# Configure 'max_slot_wal_keep_size = 1' on the publisher and
+# reload configuration
+$node_p->append_conf('postgresql.conf', 'max_slot_wal_keep_size = 1');
+$node_p->reload;
+
+# dry run mode on node S and verify the warning message for misconfigured
+# 'max_slot_wal_keep_size'
+command_checks_all(
 	[
 		'pg_createsubscriber', '--verbose',
 		'--recovery-timeout', "$PostgreSQL::Test::Utils::timeout_default",
@@ -335,7 +341,19 @@ command_ok(
 		$db1, '--database',
 		$db2
 	],
-	'run pg_createsubscriber --dry-run on node S');
+	0,
+	[qr/./],
+	[
+		qr/pg_createsubscriber: warning: publisher requires WAL size must not be restricted/,
+		qr/The max_slot_wal_keep_size parameter is currently set to a non-default value, which may lead to replication failures. /,
+		qr/This parameter must be set to -1 to ensure that required WAL files are not prematurely removed./,
+	],
+	'Validate warning for misconfigured max_slot_wal_keep_size on the publisher'
+);
+
+# Reset 'max_slot_wal_keep_size' to default after the test
+$node_p->append_conf('postgresql.conf', 'max_slot_wal_keep_size = -1');
+$node_p->reload;
 
 # Check if node S is still a standby
 $node_s->start;
-- 
2.41.0.windows.3

From dd321e23705df5ca462486e2450fc3827c1f26c1 Mon Sep 17 00:00:00 2001
From: Khanna <Shubham.Khanna@fujitsu.com>
Date: Tue, 24 Dec 2024 12:27:27 +0530
Subject: [PATCH v6] Validate-max_slot_wal_keep_size-in-pg_createsubscriber

This patch introduces validation for the 'max_slot_wal_keep_size' GUC in the
'pg_createsubscriber' utility. The utility now checks that the publisher's
'max_slot_wal_keep_size' is set to '-1' during subscription creation.
This ensures proper functioning of logical replication slots.

The 'pg_createsubscriber' utility is updated to fetch and validate the
'max_slot_wal_keep_size' setting from the publisher. A warning is raised during
the '--dry-run' mode if the configuration is set to a non-default value.

By ensuring 'max_slot_wal_keep_size' is -1, this patch prevents the potential
deletion of required WAL files on the publisher that could disrupt logical
replication. A test case has been added to validate correct warning reporting
when 'max_slot_wal_keep_size' is misconfigured.
---
 doc/src/sgml/ref/pg_createsubscriber.sgml     |  7 ++++++
 src/bin/pg_basebackup/pg_createsubscriber.c   | 20 +++++++++++++++-
 .../t/040_pg_createsubscriber.pl              | 23 ++++++++++++++++---
 3 files changed, 46 insertions(+), 4 deletions(-)

diff --git a/doc/src/sgml/ref/pg_createsubscriber.sgml b/doc/src/sgml/ref/pg_createsubscriber.sgml
index 26b8e64a4e..c5ee5f4eba 100644
--- a/doc/src/sgml/ref/pg_createsubscriber.sgml
+++ b/doc/src/sgml/ref/pg_createsubscriber.sgml
@@ -313,6 +313,13 @@ PostgreSQL documentation
     linkend="guc-max-wal-senders"/> configured to a value greater than or equal
     to the number of specified databases and existing WAL sender processes.
    </para>
+
+   <para>
+   Replication failures can occur if required WAL files are prematurely deleted.
+   To prevent this, the source server must set <xref
+   linkend="guc-max-slot-wal-keep-size"/>  to <literal>-1</literal>, ensuring
+   WAL files are not automatically removed.
+   </para>
   </refsect2>
 
   <refsect2>
diff --git a/src/bin/pg_basebackup/pg_createsubscriber.c b/src/bin/pg_basebackup/pg_createsubscriber.c
index faf18ccf13..2a84750c8e 100644
--- a/src/bin/pg_basebackup/pg_createsubscriber.c
+++ b/src/bin/pg_basebackup/pg_createsubscriber.c
@@ -849,6 +849,7 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 	int			max_walsenders;
 	int			cur_walsenders;
 	int			max_prepared_transactions;
+	int			max_slot_wal_keep_size;
 
 	pg_log_info("checking settings on publisher");
 
@@ -872,6 +873,7 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 	 * - wal_level = logical
 	 * - max_replication_slots >= current + number of dbs to be converted
 	 * - max_wal_senders >= current + number of dbs to be converted
+	 * - max_slot_wal_keep_size = -1 (to prevent deletion of required WAL files)
 	 * -----------------------------------------------------------------------
 	 */
 	res = PQexec(conn,
@@ -880,7 +882,8 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 				 " (SELECT count(*) FROM pg_catalog.pg_replication_slots),"
 				 " pg_catalog.current_setting('max_wal_senders'),"
 				 " (SELECT count(*) FROM pg_catalog.pg_stat_activity WHERE backend_type = 'walsender'),"
-				 " pg_catalog.current_setting('max_prepared_transactions')");
+				 " pg_catalog.current_setting('max_prepared_transactions'),"
+				 " pg_catalog.current_setting('max_slot_wal_keep_size')");
 
 	if (PQresultStatus(res) != PGRES_TUPLES_OK)
 	{
@@ -895,6 +898,7 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 	max_walsenders = atoi(PQgetvalue(res, 0, 3));
 	cur_walsenders = atoi(PQgetvalue(res, 0, 4));
 	max_prepared_transactions = atoi(PQgetvalue(res, 0, 5));
+	max_slot_wal_keep_size = atoi(PQgetvalue(res, 0, 6));
 
 	PQclear(res);
 
@@ -905,6 +909,8 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 	pg_log_debug("publisher: current wal senders: %d", cur_walsenders);
 	pg_log_debug("publisher: max_prepared_transactions: %d",
 				 max_prepared_transactions);
+	pg_log_debug("publisher: max_slot_wal_keep_size: %d",
+				 max_slot_wal_keep_size);
 
 	disconnect_database(conn, false);
 
@@ -939,6 +945,18 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 							  "Prepared transactions will be replicated at COMMIT PREPARED.");
 	}
 
+	/*
+	 * Validate 'max_slot_wal_keep_size'. If this parameter is set to a
+	 * non-default value, it may cause replication failures due to required
+	 * WAL files being prematurely removed.
+	 */
+	if (dry_run && max_slot_wal_keep_size != -1)
+	{
+		pg_log_warning("publisher requires WAL size must not be restricted");
+		pg_log_warning_hint("Set the configuration parameter \"%s\" to -1 to ensure that required WAL files are not prematurely removed.",
+							"max_slot_wal_keep_size");
+	}
+
 	pg_free(wal_level);
 
 	if (failed)
diff --git a/src/bin/pg_basebackup/t/040_pg_createsubscriber.pl b/src/bin/pg_basebackup/t/040_pg_createsubscriber.pl
index 5426159fa5..76c42c19c7 100644
--- a/src/bin/pg_basebackup/t/040_pg_createsubscriber.pl
+++ b/src/bin/pg_basebackup/t/040_pg_createsubscriber.pl
@@ -318,8 +318,14 @@ $node_p->safe_psql($db1,
 $node_p->wait_for_replay_catchup($node_s);
 $node_s->stop;
 
-# dry run mode on node S
-command_ok(
+# Configure 'max_slot_wal_keep_size = 1' on the publisher and
+# reload configuration
+$node_p->append_conf('postgresql.conf', 'max_slot_wal_keep_size = 1');
+$node_p->reload;
+
+# dry run mode on node S and verify the warning message for misconfigured
+# 'max_slot_wal_keep_size'
+command_checks_all(
 	[
 		'pg_createsubscriber', '--verbose',
 		'--recovery-timeout', "$PostgreSQL::Test::Utils::timeout_default",
@@ -335,7 +341,18 @@ command_ok(
 		$db1, '--database',
 		$db2
 	],
-	'run pg_createsubscriber --dry-run on node S');
+	0,
+	[qr/./],
+	[
+		qr/pg_createsubscriber: warning: publisher requires WAL size must not be restricted/,
+		qr/Set the configuration parameter "max_slot_wal_keep_size" to -1 to ensure that required WAL files are not prematurely removed./,
+	],
+	'Validate warning for misconfigured max_slot_wal_keep_size on the publisher'
+);
+
+# Reset 'max_slot_wal_keep_size' to default after the test
+$node_p->append_conf('postgresql.conf', 'max_slot_wal_keep_size = -1');
+$node_p->reload;
 
 # Check if node S is still a standby
 $node_s->start;
-- 
2.34.1

diff --git a/doc/src/sgml/ref/pg_createsubscriber.sgml b/doc/src/sgml/ref/pg_createsubscriber.sgml
index c5ee5f4..40b8fac 100644
--- a/doc/src/sgml/ref/pg_createsubscriber.sgml
+++ b/doc/src/sgml/ref/pg_createsubscriber.sgml
@@ -315,10 +315,10 @@ PostgreSQL documentation
    </para>
 
    <para>
-   Replication failures can occur if required WAL files are prematurely deleted.
-   To prevent this, the source server must set <xref
-   linkend="guc-max-slot-wal-keep-size"/>  to <literal>-1</literal>, ensuring
-   WAL files are not automatically removed.
+   Replication failures can occur if required WAL files are missing. To prevent
+   this, the source server must set <xref linkend="guc-max-slot-wal-keep-size"/>
+   to <literal>-1</literal> to ensure that required WAL files are not
+   prematurely removed.
    </para>
   </refsect2>
 

From 191c60c758770f00d64b432ce2b1e9aaeb8deb05 Mon Sep 17 00:00:00 2001
From: Khanna <Shubham.Khanna@fujitsu.com>
Date: Tue, 24 Dec 2024 12:27:27 +0530
Subject: [PATCH v7] Validate-max_slot_wal_keep_size-in-pg_createsubscriber

This patch introduces validation for the 'max_slot_wal_keep_size' GUC in the
'pg_createsubscriber' utility. The utility now checks that the publisher's
'max_slot_wal_keep_size' is set to '-1' during subscription creation.
This ensures proper functioning of logical replication slots.

The 'pg_createsubscriber' utility is updated to fetch and validate the
'max_slot_wal_keep_size' setting from the publisher. A warning is raised during
the '--dry-run' mode if the configuration is set to a non-default value.

By ensuring 'max_slot_wal_keep_size' is -1, this patch prevents the potential
deletion of required WAL files on the publisher that could disrupt logical
replication. A test case has been added to validate correct warning reporting
when 'max_slot_wal_keep_size' is misconfigured.
---
 doc/src/sgml/ref/pg_createsubscriber.sgml     |  7 +++++
 src/bin/pg_basebackup/pg_createsubscriber.c   | 28 ++++++++++++++++++-
 .../t/040_pg_createsubscriber.pl              | 23 +++++++++++++--
 3 files changed, 54 insertions(+), 4 deletions(-)

diff --git a/doc/src/sgml/ref/pg_createsubscriber.sgml b/doc/src/sgml/ref/pg_createsubscriber.sgml
index 26b8e64a4e..40b8fac50e 100644
--- a/doc/src/sgml/ref/pg_createsubscriber.sgml
+++ b/doc/src/sgml/ref/pg_createsubscriber.sgml
@@ -313,6 +313,13 @@ PostgreSQL documentation
     linkend="guc-max-wal-senders"/> configured to a value greater than or equal
     to the number of specified databases and existing WAL sender processes.
    </para>
+
+   <para>
+   Replication failures can occur if required WAL files are missing. To prevent
+   this, the source server must set <xref linkend="guc-max-slot-wal-keep-size"/>
+   to <literal>-1</literal> to ensure that required WAL files are not
+   prematurely removed.
+   </para>
   </refsect2>
 
   <refsect2>
diff --git a/src/bin/pg_basebackup/pg_createsubscriber.c b/src/bin/pg_basebackup/pg_createsubscriber.c
index faf18ccf13..d5dcd290c9 100644
--- a/src/bin/pg_basebackup/pg_createsubscriber.c
+++ b/src/bin/pg_basebackup/pg_createsubscriber.c
@@ -27,6 +27,7 @@
 #include "fe_utils/simple_list.h"
 #include "fe_utils/string_utils.h"
 #include "getopt_long.h"
+#include "common/int.h"			/* include for strtoi64 */
 
 #define	DEFAULT_SUB_PORT	"50432"
 
@@ -849,6 +850,7 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 	int			max_walsenders;
 	int			cur_walsenders;
 	int			max_prepared_transactions;
+	int64		max_slot_wal_keep_size;
 
 	pg_log_info("checking settings on publisher");
 
@@ -872,6 +874,7 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 	 * - wal_level = logical
 	 * - max_replication_slots >= current + number of dbs to be converted
 	 * - max_wal_senders >= current + number of dbs to be converted
+	 * - max_slot_wal_keep_size = -1 (to prevent deletion of required WAL files)
 	 * -----------------------------------------------------------------------
 	 */
 	res = PQexec(conn,
@@ -880,7 +883,8 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 				 " (SELECT count(*) FROM pg_catalog.pg_replication_slots),"
 				 " pg_catalog.current_setting('max_wal_senders'),"
 				 " (SELECT count(*) FROM pg_catalog.pg_stat_activity WHERE backend_type = 'walsender'),"
-				 " pg_catalog.current_setting('max_prepared_transactions')");
+				 " pg_catalog.current_setting('max_prepared_transactions'),"
+				 " pg_catalog.pg_size_bytes(pg_catalog.current_setting('max_slot_wal_keep_size'))");
 
 	if (PQresultStatus(res) != PGRES_TUPLES_OK)
 	{
@@ -895,6 +899,14 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 	max_walsenders = atoi(PQgetvalue(res, 0, 3));
 	cur_walsenders = atoi(PQgetvalue(res, 0, 4));
 	max_prepared_transactions = atoi(PQgetvalue(res, 0, 5));
+	max_slot_wal_keep_size = strtoi64(PQgetvalue(res, 0, 6), NULL, 0);
+
+	/* use strtoi64 to convert the string result to a 64-bit integer */
+	if (max_slot_wal_keep_size == 0 && errno != 0)
+	{
+		/* handle conversion error */
+		pg_log_error("Failed to convert max_slot_wal_keep_size to int64");
+	}
 
 	PQclear(res);
 
@@ -905,6 +917,8 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 	pg_log_debug("publisher: current wal senders: %d", cur_walsenders);
 	pg_log_debug("publisher: max_prepared_transactions: %d",
 				 max_prepared_transactions);
+	pg_log_debug("publisher: max_slot_wal_keep_size: %ld",
+				 max_slot_wal_keep_size);
 
 	disconnect_database(conn, false);
 
@@ -939,6 +953,18 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 							  "Prepared transactions will be replicated at COMMIT PREPARED.");
 	}
 
+	/*
+	 * Validate 'max_slot_wal_keep_size'. If this parameter is set to a
+	 * non-default value, it may cause replication failures due to required
+	 * WAL files being prematurely removed.
+	 */
+	if (dry_run && max_slot_wal_keep_size != -1)
+	{
+		pg_log_warning("publisher requires WAL size must not be restricted");
+		pg_log_warning_hint("Set the configuration parameter \"%s\" to -1 to ensure that required WAL files are not prematurely removed.",
+							"max_slot_wal_keep_size");
+	}
+
 	pg_free(wal_level);
 
 	if (failed)
diff --git a/src/bin/pg_basebackup/t/040_pg_createsubscriber.pl b/src/bin/pg_basebackup/t/040_pg_createsubscriber.pl
index 5426159fa5..76c42c19c7 100644
--- a/src/bin/pg_basebackup/t/040_pg_createsubscriber.pl
+++ b/src/bin/pg_basebackup/t/040_pg_createsubscriber.pl
@@ -318,8 +318,14 @@ $node_p->safe_psql($db1,
 $node_p->wait_for_replay_catchup($node_s);
 $node_s->stop;
 
-# dry run mode on node S
-command_ok(
+# Configure 'max_slot_wal_keep_size = 1' on the publisher and
+# reload configuration
+$node_p->append_conf('postgresql.conf', 'max_slot_wal_keep_size = 1');
+$node_p->reload;
+
+# dry run mode on node S and verify the warning message for misconfigured
+# 'max_slot_wal_keep_size'
+command_checks_all(
 	[
 		'pg_createsubscriber', '--verbose',
 		'--recovery-timeout', "$PostgreSQL::Test::Utils::timeout_default",
@@ -335,7 +341,18 @@ command_ok(
 		$db1, '--database',
 		$db2
 	],
-	'run pg_createsubscriber --dry-run on node S');
+	0,
+	[qr/./],
+	[
+		qr/pg_createsubscriber: warning: publisher requires WAL size must not be restricted/,
+		qr/Set the configuration parameter "max_slot_wal_keep_size" to -1 to ensure that required WAL files are not prematurely removed./,
+	],
+	'Validate warning for misconfigured max_slot_wal_keep_size on the publisher'
+);
+
+# Reset 'max_slot_wal_keep_size' to default after the test
+$node_p->append_conf('postgresql.conf', 'max_slot_wal_keep_size = -1');
+$node_p->reload;
 
 # Check if node S is still a standby
 $node_s->start;
-- 
2.34.1

From ccd1f19ccdd77ebca1272f04144d90f2a0deec14 Mon Sep 17 00:00:00 2001
From: Khanna <Shubham.Khanna@fujitsu.com>
Date: Tue, 24 Dec 2024 12:27:27 +0530
Subject: [PATCH v8] Validate-max_slot_wal_keep_size-in-pg_createsubscriber

This patch introduces validation for the 'max_slot_wal_keep_size' GUC in the
'pg_createsubscriber' utility. The utility now checks that the publisher's
'max_slot_wal_keep_size' is set to '-1' during subscription creation.
This ensures proper functioning of logical replication slots.

The 'pg_createsubscriber' utility is updated to fetch and validate the
'max_slot_wal_keep_size' setting from the publisher. A warning is raised during
the '--dry-run' mode if the configuration is set to a non-default value.

By ensuring 'max_slot_wal_keep_size' is -1, this patch prevents the potential
deletion of required WAL files on the publisher that could disrupt logical
replication. A test case has been added to validate correct warning reporting
when 'max_slot_wal_keep_size' is misconfigured.
---
 doc/src/sgml/ref/pg_createsubscriber.sgml     |  7 ++++++
 src/bin/pg_basebackup/pg_createsubscriber.c   | 20 +++++++++++++++-
 .../t/040_pg_createsubscriber.pl              | 23 ++++++++++++++++---
 3 files changed, 46 insertions(+), 4 deletions(-)

diff --git a/doc/src/sgml/ref/pg_createsubscriber.sgml b/doc/src/sgml/ref/pg_createsubscriber.sgml
index 26b8e64a4e..40b8fac50e 100644
--- a/doc/src/sgml/ref/pg_createsubscriber.sgml
+++ b/doc/src/sgml/ref/pg_createsubscriber.sgml
@@ -313,6 +313,13 @@ PostgreSQL documentation
     linkend="guc-max-wal-senders"/> configured to a value greater than or equal
     to the number of specified databases and existing WAL sender processes.
    </para>
+
+   <para>
+   Replication failures can occur if required WAL files are missing. To prevent
+   this, the source server must set <xref linkend="guc-max-slot-wal-keep-size"/>
+   to <literal>-1</literal> to ensure that required WAL files are not
+   prematurely removed.
+   </para>
   </refsect2>
 
   <refsect2>
diff --git a/src/bin/pg_basebackup/pg_createsubscriber.c b/src/bin/pg_basebackup/pg_createsubscriber.c
index faf18ccf13..f1892f3f33 100644
--- a/src/bin/pg_basebackup/pg_createsubscriber.c
+++ b/src/bin/pg_basebackup/pg_createsubscriber.c
@@ -849,6 +849,7 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 	int			max_walsenders;
 	int			cur_walsenders;
 	int			max_prepared_transactions;
+	int64		max_slot_wal_keep_size;
 
 	pg_log_info("checking settings on publisher");
 
@@ -872,6 +873,7 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 	 * - wal_level = logical
 	 * - max_replication_slots >= current + number of dbs to be converted
 	 * - max_wal_senders >= current + number of dbs to be converted
+	 * - max_slot_wal_keep_size = -1 (to prevent deletion of required WAL files)
 	 * -----------------------------------------------------------------------
 	 */
 	res = PQexec(conn,
@@ -880,7 +882,8 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 				 " (SELECT count(*) FROM pg_catalog.pg_replication_slots),"
 				 " pg_catalog.current_setting('max_wal_senders'),"
 				 " (SELECT count(*) FROM pg_catalog.pg_stat_activity WHERE backend_type = 'walsender'),"
-				 " pg_catalog.current_setting('max_prepared_transactions')");
+				 " pg_catalog.current_setting('max_prepared_transactions'),"
+				 " pg_catalog.pg_size_bytes(pg_catalog.current_setting('max_slot_wal_keep_size'))");
 
 	if (PQresultStatus(res) != PGRES_TUPLES_OK)
 	{
@@ -895,6 +898,7 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 	max_walsenders = atoi(PQgetvalue(res, 0, 3));
 	cur_walsenders = atoi(PQgetvalue(res, 0, 4));
 	max_prepared_transactions = atoi(PQgetvalue(res, 0, 5));
+	max_slot_wal_keep_size = strtoi64(PQgetvalue(res, 0, 6), NULL, 0);
 
 	PQclear(res);
 
@@ -905,6 +909,8 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 	pg_log_debug("publisher: current wal senders: %d", cur_walsenders);
 	pg_log_debug("publisher: max_prepared_transactions: %d",
 				 max_prepared_transactions);
+	pg_log_debug("publisher: max_slot_wal_keep_size: " INT64_FORMAT,
+				 max_slot_wal_keep_size);
 
 	disconnect_database(conn, false);
 
@@ -939,6 +945,18 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 							  "Prepared transactions will be replicated at COMMIT PREPARED.");
 	}
 
+	/*
+	 * Validate 'max_slot_wal_keep_size'. If this parameter is set to a
+	 * non-default value, it may cause replication failures due to required
+	 * WAL files being prematurely removed.
+	 */
+	if (dry_run && max_slot_wal_keep_size != -1)
+	{
+		pg_log_warning("publisher requires WAL size must not be restricted");
+		pg_log_warning_hint("Set the configuration parameter \"%s\" to -1 to ensure that required WAL files are not prematurely removed.",
+							"max_slot_wal_keep_size");
+	}
+
 	pg_free(wal_level);
 
 	if (failed)
diff --git a/src/bin/pg_basebackup/t/040_pg_createsubscriber.pl b/src/bin/pg_basebackup/t/040_pg_createsubscriber.pl
index 5426159fa5..c1fc0cfe9e 100644
--- a/src/bin/pg_basebackup/t/040_pg_createsubscriber.pl
+++ b/src/bin/pg_basebackup/t/040_pg_createsubscriber.pl
@@ -318,8 +318,14 @@ $node_p->safe_psql($db1,
 $node_p->wait_for_replay_catchup($node_s);
 $node_s->stop;
 
-# dry run mode on node S
-command_ok(
+# Configure 'max_slot_wal_keep_size = 10MB' on the publisher and
+# reload configuration
+$node_p->append_conf('postgresql.conf', 'max_slot_wal_keep_size = 10MB');
+$node_p->reload;
+
+# dry run mode on node S and verify the warning message for misconfigured
+# 'max_slot_wal_keep_size'
+command_checks_all(
 	[
 		'pg_createsubscriber', '--verbose',
 		'--recovery-timeout', "$PostgreSQL::Test::Utils::timeout_default",
@@ -335,7 +341,18 @@ command_ok(
 		$db1, '--database',
 		$db2
 	],
-	'run pg_createsubscriber --dry-run on node S');
+	0,
+	[qr/./],
+	[
+		qr/pg_createsubscriber: warning: publisher requires WAL size must not be restricted/,
+		qr/Set the configuration parameter "max_slot_wal_keep_size" to -1 to ensure that required WAL files are not prematurely removed./,
+	],
+	'Validate warning for misconfigured max_slot_wal_keep_size on the publisher'
+);
+
+# Reset 'max_slot_wal_keep_size' to default after the test
+$node_p->append_conf('postgresql.conf', 'max_slot_wal_keep_size = -1');
+$node_p->reload;
 
 # Check if node S is still a standby
 $node_s->start;
-- 
2.34.1

diff --git a/src/bin/pg_basebackup/t/040_pg_createsubscriber.pl b/src/bin/pg_basebackup/t/040_pg_createsubscriber.pl
index c1fc0cf..773a27b 100644
--- a/src/bin/pg_basebackup/t/040_pg_createsubscriber.pl
+++ b/src/bin/pg_basebackup/t/040_pg_createsubscriber.pl
@@ -327,7 +327,7 @@ $node_p->reload;
 # 'max_slot_wal_keep_size'
 command_checks_all(
 	[
-		'pg_createsubscriber', '--verbose',
+		'pg_createsubscriber', '--verbose', '--verbose',
 		'--recovery-timeout', "$PostgreSQL::Test::Utils::timeout_default",
 		'--dry-run', '--pgdata',
 		$node_s->data_dir, '--publisher-server',
@@ -350,6 +350,26 @@ command_checks_all(
 	'Validate warning for misconfigured max_slot_wal_keep_size on the publisher'
 );
 
+# And, same again to see the output...
+command_ok(
+	[
+		'pg_createsubscriber', '--verbose', '--verbose',
+		'--recovery-timeout', "$PostgreSQL::Test::Utils::timeout_default",
+		'--dry-run', '--pgdata',
+		$node_s->data_dir, '--publisher-server',
+		$node_p->connstr($db1), '--socketdir',
+		$node_s->host, '--subscriber-port',
+		$node_s->port, '--publication',
+		'pub1', '--publication',
+		'pub2', '--subscription',
+		'sub1', '--subscription',
+		'sub2', '--database',
+		$db1, '--database',
+		$db2
+	],
+	'Ditto above, but this time using command_ok to retain the output'
+);
+
 # Reset 'max_slot_wal_keep_size' to default after the test
 $node_p->append_conf('postgresql.conf', 'max_slot_wal_keep_size = -1');
 $node_p->reload;

From 52edb90bd8bca67948fabc7a22c7708add3e186c Mon Sep 17 00:00:00 2001
From: Khanna <Shubham.Khanna@fujitsu.com>
Date: Tue, 24 Dec 2024 12:27:27 +0530
Subject: [PATCH v9] Validate-max_slot_wal_keep_size-in-pg_createsubscriber

This patch introduces validation for the 'max_slot_wal_keep_size' GUC in the
'pg_createsubscriber' utility. The utility now checks that the publisher's
'max_slot_wal_keep_size' is set to '-1' during subscription creation.
This ensures proper functioning of logical replication slots.

The 'pg_createsubscriber' utility is updated to fetch and validate the
'max_slot_wal_keep_size' setting from the publisher. A warning is raised during
the '--dry-run' mode if the configuration is set to a non-default value.

This patch logs a warning if 'max_slot_wal_keep_size' is not set to '-1',
highlighting a potential risk of required WAL files being deleted on the
publisher, which could disrupt logical replication.
A test case has been added to validate correct warning reporting
when 'max_slot_wal_keep_size' is misconfigured.
---
 doc/src/sgml/ref/pg_createsubscriber.sgml     |  7 +++
 src/bin/pg_basebackup/pg_createsubscriber.c   | 20 ++++++++-
 .../t/040_pg_createsubscriber.pl              | 43 +++++++++++++++++--
 3 files changed, 66 insertions(+), 4 deletions(-)

diff --git a/doc/src/sgml/ref/pg_createsubscriber.sgml b/doc/src/sgml/ref/pg_createsubscriber.sgml
index 26b8e64a4e..40b8fac50e 100644
--- a/doc/src/sgml/ref/pg_createsubscriber.sgml
+++ b/doc/src/sgml/ref/pg_createsubscriber.sgml
@@ -313,6 +313,13 @@ PostgreSQL documentation
     linkend="guc-max-wal-senders"/> configured to a value greater than or equal
     to the number of specified databases and existing WAL sender processes.
    </para>
+
+   <para>
+   Replication failures can occur if required WAL files are missing. To prevent
+   this, the source server must set <xref linkend="guc-max-slot-wal-keep-size"/>
+   to <literal>-1</literal> to ensure that required WAL files are not
+   prematurely removed.
+   </para>
   </refsect2>
 
   <refsect2>
diff --git a/src/bin/pg_basebackup/pg_createsubscriber.c b/src/bin/pg_basebackup/pg_createsubscriber.c
index faf18ccf13..7433c7ae2a 100644
--- a/src/bin/pg_basebackup/pg_createsubscriber.c
+++ b/src/bin/pg_basebackup/pg_createsubscriber.c
@@ -849,6 +849,7 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 	int			max_walsenders;
 	int			cur_walsenders;
 	int			max_prepared_transactions;
+	char	   *max_slot_wal_keep_size;
 
 	pg_log_info("checking settings on publisher");
 
@@ -872,6 +873,7 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 	 * - wal_level = logical
 	 * - max_replication_slots >= current + number of dbs to be converted
 	 * - max_wal_senders >= current + number of dbs to be converted
+	 * - max_slot_wal_keep_size = -1 (to prevent deletion of required WAL files)
 	 * -----------------------------------------------------------------------
 	 */
 	res = PQexec(conn,
@@ -880,7 +882,8 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 				 " (SELECT count(*) FROM pg_catalog.pg_replication_slots),"
 				 " pg_catalog.current_setting('max_wal_senders'),"
 				 " (SELECT count(*) FROM pg_catalog.pg_stat_activity WHERE backend_type = 'walsender'),"
-				 " pg_catalog.current_setting('max_prepared_transactions')");
+				 " pg_catalog.current_setting('max_prepared_transactions'),"
+				 " pg_catalog.current_setting('max_slot_wal_keep_size')");
 
 	if (PQresultStatus(res) != PGRES_TUPLES_OK)
 	{
@@ -895,6 +898,7 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 	max_walsenders = atoi(PQgetvalue(res, 0, 3));
 	cur_walsenders = atoi(PQgetvalue(res, 0, 4));
 	max_prepared_transactions = atoi(PQgetvalue(res, 0, 5));
+	max_slot_wal_keep_size = pg_strdup(PQgetvalue(res, 0, 6));
 
 	PQclear(res);
 
@@ -905,6 +909,8 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 	pg_log_debug("publisher: current wal senders: %d", cur_walsenders);
 	pg_log_debug("publisher: max_prepared_transactions: %d",
 				 max_prepared_transactions);
+	pg_log_debug("publisher: max_slot_wal_keep_size: %s",
+				 max_slot_wal_keep_size);
 
 	disconnect_database(conn, false);
 
@@ -939,6 +945,18 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 							  "Prepared transactions will be replicated at COMMIT PREPARED.");
 	}
 
+	/*
+	 * Validate 'max_slot_wal_keep_size'. If this parameter is set to a
+	 * non-default value, it may cause replication failures due to required
+	 * WAL files being prematurely removed.
+	 */
+	if (dry_run && (strcmp(max_slot_wal_keep_size, "-1") != 0))
+	{
+		pg_log_warning("publisher requires WAL size must not be restricted");
+		pg_log_warning_hint("Set the configuration parameter \"%s\" to -1 to ensure that required WAL files are not prematurely removed.",
+							"max_slot_wal_keep_size");
+	}
+
 	pg_free(wal_level);
 
 	if (failed)
diff --git a/src/bin/pg_basebackup/t/040_pg_createsubscriber.pl b/src/bin/pg_basebackup/t/040_pg_createsubscriber.pl
index 5426159fa5..773a27bf06 100644
--- a/src/bin/pg_basebackup/t/040_pg_createsubscriber.pl
+++ b/src/bin/pg_basebackup/t/040_pg_createsubscriber.pl
@@ -318,10 +318,42 @@ $node_p->safe_psql($db1,
 $node_p->wait_for_replay_catchup($node_s);
 $node_s->stop;
 
-# dry run mode on node S
+# Configure 'max_slot_wal_keep_size = 10MB' on the publisher and
+# reload configuration
+$node_p->append_conf('postgresql.conf', 'max_slot_wal_keep_size = 10MB');
+$node_p->reload;
+
+# dry run mode on node S and verify the warning message for misconfigured
+# 'max_slot_wal_keep_size'
+command_checks_all(
+	[
+		'pg_createsubscriber', '--verbose', '--verbose',
+		'--recovery-timeout', "$PostgreSQL::Test::Utils::timeout_default",
+		'--dry-run', '--pgdata',
+		$node_s->data_dir, '--publisher-server',
+		$node_p->connstr($db1), '--socketdir',
+		$node_s->host, '--subscriber-port',
+		$node_s->port, '--publication',
+		'pub1', '--publication',
+		'pub2', '--subscription',
+		'sub1', '--subscription',
+		'sub2', '--database',
+		$db1, '--database',
+		$db2
+	],
+	0,
+	[qr/./],
+	[
+		qr/pg_createsubscriber: warning: publisher requires WAL size must not be restricted/,
+		qr/Set the configuration parameter "max_slot_wal_keep_size" to -1 to ensure that required WAL files are not prematurely removed./,
+	],
+	'Validate warning for misconfigured max_slot_wal_keep_size on the publisher'
+);
+
+# And, same again to see the output...
 command_ok(
 	[
-		'pg_createsubscriber', '--verbose',
+		'pg_createsubscriber', '--verbose', '--verbose',
 		'--recovery-timeout', "$PostgreSQL::Test::Utils::timeout_default",
 		'--dry-run', '--pgdata',
 		$node_s->data_dir, '--publisher-server',
@@ -335,7 +367,12 @@ command_ok(
 		$db1, '--database',
 		$db2
 	],
-	'run pg_createsubscriber --dry-run on node S');
+	'Ditto above, but this time using command_ok to retain the output'
+);
+
+# Reset 'max_slot_wal_keep_size' to default after the test
+$node_p->append_conf('postgresql.conf', 'max_slot_wal_keep_size = -1');
+$node_p->reload;
 
 # Check if node S is still a standby
 $node_s->start;
-- 
2.41.0.windows.3

From 07a34d2541687779fb07ce1a294454659279b4e2 Mon Sep 17 00:00:00 2001
From: Khanna <Shubham.Khanna@fujitsu.com>
Date: Tue, 24 Dec 2024 12:27:27 +0530
Subject: [PATCH v10] Validate-max_slot_wal_keep_size-in-pg_createsubscriber

This patch introduces validation for the 'max_slot_wal_keep_size' GUC in the
'pg_createsubscriber' utility. The utility now checks that the publisher's
'max_slot_wal_keep_size' is set to '-1' during subscription creation.
This ensures proper functioning of logical replication slots.

The 'pg_createsubscriber' utility is updated to fetch and validate the
'max_slot_wal_keep_size' setting from the publisher. A warning is raised during
the '--dry-run' mode if the configuration is set to a non-default value.

This patch logs a warning if 'max_slot_wal_keep_size' is not set to '-1',
highlighting a potential risk of required WAL files being deleted on the
publisher, which could disrupt logical replication.
A test case has been added to validate correct warning reporting
when 'max_slot_wal_keep_size' is misconfigured.
---
 doc/src/sgml/ref/pg_createsubscriber.sgml     |  7 ++
 src/bin/pg_basebackup/pg_createsubscriber.c   | 20 +++++-
 .../t/040_pg_createsubscriber.pl              | 64 +++++++++++++++----
 3 files changed, 76 insertions(+), 15 deletions(-)

diff --git a/doc/src/sgml/ref/pg_createsubscriber.sgml b/doc/src/sgml/ref/pg_createsubscriber.sgml
index 26b8e64a4e..40b8fac50e 100644
--- a/doc/src/sgml/ref/pg_createsubscriber.sgml
+++ b/doc/src/sgml/ref/pg_createsubscriber.sgml
@@ -313,6 +313,13 @@ PostgreSQL documentation
     linkend="guc-max-wal-senders"/> configured to a value greater than or equal
     to the number of specified databases and existing WAL sender processes.
    </para>
+
+   <para>
+   Replication failures can occur if required WAL files are missing. To prevent
+   this, the source server must set <xref linkend="guc-max-slot-wal-keep-size"/>
+   to <literal>-1</literal> to ensure that required WAL files are not
+   prematurely removed.
+   </para>
   </refsect2>
 
   <refsect2>
diff --git a/src/bin/pg_basebackup/pg_createsubscriber.c b/src/bin/pg_basebackup/pg_createsubscriber.c
index faf18ccf13..7433c7ae2a 100644
--- a/src/bin/pg_basebackup/pg_createsubscriber.c
+++ b/src/bin/pg_basebackup/pg_createsubscriber.c
@@ -849,6 +849,7 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 	int			max_walsenders;
 	int			cur_walsenders;
 	int			max_prepared_transactions;
+	char	   *max_slot_wal_keep_size;
 
 	pg_log_info("checking settings on publisher");
 
@@ -872,6 +873,7 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 	 * - wal_level = logical
 	 * - max_replication_slots >= current + number of dbs to be converted
 	 * - max_wal_senders >= current + number of dbs to be converted
+	 * - max_slot_wal_keep_size = -1 (to prevent deletion of required WAL files)
 	 * -----------------------------------------------------------------------
 	 */
 	res = PQexec(conn,
@@ -880,7 +882,8 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 				 " (SELECT count(*) FROM pg_catalog.pg_replication_slots),"
 				 " pg_catalog.current_setting('max_wal_senders'),"
 				 " (SELECT count(*) FROM pg_catalog.pg_stat_activity WHERE backend_type = 'walsender'),"
-				 " pg_catalog.current_setting('max_prepared_transactions')");
+				 " pg_catalog.current_setting('max_prepared_transactions'),"
+				 " pg_catalog.current_setting('max_slot_wal_keep_size')");
 
 	if (PQresultStatus(res) != PGRES_TUPLES_OK)
 	{
@@ -895,6 +898,7 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 	max_walsenders = atoi(PQgetvalue(res, 0, 3));
 	cur_walsenders = atoi(PQgetvalue(res, 0, 4));
 	max_prepared_transactions = atoi(PQgetvalue(res, 0, 5));
+	max_slot_wal_keep_size = pg_strdup(PQgetvalue(res, 0, 6));
 
 	PQclear(res);
 
@@ -905,6 +909,8 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 	pg_log_debug("publisher: current wal senders: %d", cur_walsenders);
 	pg_log_debug("publisher: max_prepared_transactions: %d",
 				 max_prepared_transactions);
+	pg_log_debug("publisher: max_slot_wal_keep_size: %s",
+				 max_slot_wal_keep_size);
 
 	disconnect_database(conn, false);
 
@@ -939,6 +945,18 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 							  "Prepared transactions will be replicated at COMMIT PREPARED.");
 	}
 
+	/*
+	 * Validate 'max_slot_wal_keep_size'. If this parameter is set to a
+	 * non-default value, it may cause replication failures due to required
+	 * WAL files being prematurely removed.
+	 */
+	if (dry_run && (strcmp(max_slot_wal_keep_size, "-1") != 0))
+	{
+		pg_log_warning("publisher requires WAL size must not be restricted");
+		pg_log_warning_hint("Set the configuration parameter \"%s\" to -1 to ensure that required WAL files are not prematurely removed.",
+							"max_slot_wal_keep_size");
+	}
+
 	pg_free(wal_level);
 
 	if (failed)
diff --git a/src/bin/pg_basebackup/t/040_pg_createsubscriber.pl b/src/bin/pg_basebackup/t/040_pg_createsubscriber.pl
index 5426159fa5..d55fd78009 100644
--- a/src/bin/pg_basebackup/t/040_pg_createsubscriber.pl
+++ b/src/bin/pg_basebackup/t/040_pg_createsubscriber.pl
@@ -318,24 +318,60 @@ $node_p->safe_psql($db1,
 $node_p->wait_for_replay_catchup($node_s);
 $node_s->stop;
 
-# dry run mode on node S
+# Configure 'max_slot_wal_keep_size = 10MB' on the publisher and
+# reload configuration
+$node_p->append_conf('postgresql.conf', 'max_slot_wal_keep_size = 10MB');
+$node_p->reload;
+
+# dry run mode on node S and verify the warning message for misconfigured
+# 'max_slot_wal_keep_size'
+command_checks_all(
+	[
+		'pg_createsubscriber', '--verbose',
+		'--verbose', '--recovery-timeout',
+		"$PostgreSQL::Test::Utils::timeout_default", '--dry-run',
+		'--pgdata', $node_s->data_dir,
+		'--publisher-server', $node_p->connstr($db1),
+		'--socketdir', $node_s->host,
+		'--subscriber-port', $node_s->port,
+		'--publication', 'pub1',
+		'--publication', 'pub2',
+		'--subscription', 'sub1',
+		'--subscription', 'sub2',
+		'--database', $db1,
+		'--database', $db2
+	],
+	0,
+	[qr/./],
+	[
+		qr/pg_createsubscriber: warning: publisher requires WAL size must not be restricted/,
+		qr/Set the configuration parameter "max_slot_wal_keep_size" to -1 to ensure that required WAL files are not prematurely removed./,
+	],
+	'Validate warning for misconfigured max_slot_wal_keep_size on the publisher'
+);
+
+# And, same again to see the output...
 command_ok(
 	[
 		'pg_createsubscriber', '--verbose',
-		'--recovery-timeout', "$PostgreSQL::Test::Utils::timeout_default",
-		'--dry-run', '--pgdata',
-		$node_s->data_dir, '--publisher-server',
-		$node_p->connstr($db1), '--socketdir',
-		$node_s->host, '--subscriber-port',
-		$node_s->port, '--publication',
-		'pub1', '--publication',
-		'pub2', '--subscription',
-		'sub1', '--subscription',
-		'sub2', '--database',
-		$db1, '--database',
-		$db2
+		'--verbose', '--recovery-timeout',
+		"$PostgreSQL::Test::Utils::timeout_default", '--dry-run',
+		'--pgdata', $node_s->data_dir,
+		'--publisher-server', $node_p->connstr($db1),
+		'--socketdir', $node_s->host,
+		'--subscriber-port', $node_s->port,
+		'--publication', 'pub1',
+		'--publication', 'pub2',
+		'--subscription', 'sub1',
+		'--subscription', 'sub2',
+		'--database', $db1,
+		'--database', $db2
 	],
-	'run pg_createsubscriber --dry-run on node S');
+	'Ditto above, but this time using command_ok to retain the output');
+
+# Reset 'max_slot_wal_keep_size' to default after the test
+$node_p->append_conf('postgresql.conf', 'max_slot_wal_keep_size = -1');
+$node_p->reload;
 
 # Check if node S is still a standby
 $node_s->start;
-- 
2.34.1

From 4d1532fd5ffa3715d69049971272d9f4a3e13455 Mon Sep 17 00:00:00 2001
From: Khanna <Shubham.Khanna@fujitsu.com>
Date: Tue, 24 Dec 2024 12:27:27 +0530
Subject: [PATCH v11] Validate-max_slot_wal_keep_size-in-pg_createsubscriber

This patch introduces validation for the 'max_slot_wal_keep_size' GUC in the
'pg_createsubscriber' utility. The utility now checks that the publisher's
'max_slot_wal_keep_size' is set to '-1' during subscription creation.
This ensures proper functioning of logical replication slots.

The 'pg_createsubscriber' utility is updated to fetch and validate the
'max_slot_wal_keep_size' setting from the publisher. A warning is raised during
the '--dry-run' mode if the configuration is set to a non-default value.

This patch logs a warning if 'max_slot_wal_keep_size' is not set to '-1',
highlighting a potential risk of required WAL files being deleted on the
publisher, which could disrupt logical replication.
A test case has been added to validate correct warning reporting
when 'max_slot_wal_keep_size' is misconfigured.
---
 doc/src/sgml/ref/pg_createsubscriber.sgml     |  7 ++
 src/bin/pg_basebackup/pg_createsubscriber.c   | 20 +++++-
 .../t/040_pg_createsubscriber.pl              | 64 +++++++++++++++----
 3 files changed, 76 insertions(+), 15 deletions(-)

diff --git a/doc/src/sgml/ref/pg_createsubscriber.sgml b/doc/src/sgml/ref/pg_createsubscriber.sgml
index 26b8e64a4e..d56487fe2c 100644
--- a/doc/src/sgml/ref/pg_createsubscriber.sgml
+++ b/doc/src/sgml/ref/pg_createsubscriber.sgml
@@ -377,6 +377,13 @@ PostgreSQL documentation
     server.  If the target server has a standby, replication will break and a
     fresh standby should be created.
    </para>
+
+   <para>
+    Replication failures can occur if required WAL files are missing. To prevent
+    this, the source server must set
+    <xref linkend="guc-max-slot-wal-keep-size"/> to <literal>-1</literal> to
+    ensure that required WAL files are not prematurely removed.
+   </para>
   </refsect2>
 
   <refsect2>
diff --git a/src/bin/pg_basebackup/pg_createsubscriber.c b/src/bin/pg_basebackup/pg_createsubscriber.c
index faf18ccf13..7433c7ae2a 100644
--- a/src/bin/pg_basebackup/pg_createsubscriber.c
+++ b/src/bin/pg_basebackup/pg_createsubscriber.c
@@ -849,6 +849,7 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 	int			max_walsenders;
 	int			cur_walsenders;
 	int			max_prepared_transactions;
+	char	   *max_slot_wal_keep_size;
 
 	pg_log_info("checking settings on publisher");
 
@@ -872,6 +873,7 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 	 * - wal_level = logical
 	 * - max_replication_slots >= current + number of dbs to be converted
 	 * - max_wal_senders >= current + number of dbs to be converted
+	 * - max_slot_wal_keep_size = -1 (to prevent deletion of required WAL files)
 	 * -----------------------------------------------------------------------
 	 */
 	res = PQexec(conn,
@@ -880,7 +882,8 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 				 " (SELECT count(*) FROM pg_catalog.pg_replication_slots),"
 				 " pg_catalog.current_setting('max_wal_senders'),"
 				 " (SELECT count(*) FROM pg_catalog.pg_stat_activity WHERE backend_type = 'walsender'),"
-				 " pg_catalog.current_setting('max_prepared_transactions')");
+				 " pg_catalog.current_setting('max_prepared_transactions'),"
+				 " pg_catalog.current_setting('max_slot_wal_keep_size')");
 
 	if (PQresultStatus(res) != PGRES_TUPLES_OK)
 	{
@@ -895,6 +898,7 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 	max_walsenders = atoi(PQgetvalue(res, 0, 3));
 	cur_walsenders = atoi(PQgetvalue(res, 0, 4));
 	max_prepared_transactions = atoi(PQgetvalue(res, 0, 5));
+	max_slot_wal_keep_size = pg_strdup(PQgetvalue(res, 0, 6));
 
 	PQclear(res);
 
@@ -905,6 +909,8 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 	pg_log_debug("publisher: current wal senders: %d", cur_walsenders);
 	pg_log_debug("publisher: max_prepared_transactions: %d",
 				 max_prepared_transactions);
+	pg_log_debug("publisher: max_slot_wal_keep_size: %s",
+				 max_slot_wal_keep_size);
 
 	disconnect_database(conn, false);
 
@@ -939,6 +945,18 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 							  "Prepared transactions will be replicated at COMMIT PREPARED.");
 	}
 
+	/*
+	 * Validate 'max_slot_wal_keep_size'. If this parameter is set to a
+	 * non-default value, it may cause replication failures due to required
+	 * WAL files being prematurely removed.
+	 */
+	if (dry_run && (strcmp(max_slot_wal_keep_size, "-1") != 0))
+	{
+		pg_log_warning("publisher requires WAL size must not be restricted");
+		pg_log_warning_hint("Set the configuration parameter \"%s\" to -1 to ensure that required WAL files are not prematurely removed.",
+							"max_slot_wal_keep_size");
+	}
+
 	pg_free(wal_level);
 
 	if (failed)
diff --git a/src/bin/pg_basebackup/t/040_pg_createsubscriber.pl b/src/bin/pg_basebackup/t/040_pg_createsubscriber.pl
index 5426159fa5..d55fd78009 100644
--- a/src/bin/pg_basebackup/t/040_pg_createsubscriber.pl
+++ b/src/bin/pg_basebackup/t/040_pg_createsubscriber.pl
@@ -318,24 +318,60 @@ $node_p->safe_psql($db1,
 $node_p->wait_for_replay_catchup($node_s);
 $node_s->stop;
 
-# dry run mode on node S
+# Configure 'max_slot_wal_keep_size = 10MB' on the publisher and
+# reload configuration
+$node_p->append_conf('postgresql.conf', 'max_slot_wal_keep_size = 10MB');
+$node_p->reload;
+
+# dry run mode on node S and verify the warning message for misconfigured
+# 'max_slot_wal_keep_size'
+command_checks_all(
+	[
+		'pg_createsubscriber', '--verbose',
+		'--verbose', '--recovery-timeout',
+		"$PostgreSQL::Test::Utils::timeout_default", '--dry-run',
+		'--pgdata', $node_s->data_dir,
+		'--publisher-server', $node_p->connstr($db1),
+		'--socketdir', $node_s->host,
+		'--subscriber-port', $node_s->port,
+		'--publication', 'pub1',
+		'--publication', 'pub2',
+		'--subscription', 'sub1',
+		'--subscription', 'sub2',
+		'--database', $db1,
+		'--database', $db2
+	],
+	0,
+	[qr/./],
+	[
+		qr/pg_createsubscriber: warning: publisher requires WAL size must not be restricted/,
+		qr/Set the configuration parameter "max_slot_wal_keep_size" to -1 to ensure that required WAL files are not prematurely removed./,
+	],
+	'Validate warning for misconfigured max_slot_wal_keep_size on the publisher'
+);
+
+# And, same again to see the output...
 command_ok(
 	[
 		'pg_createsubscriber', '--verbose',
-		'--recovery-timeout', "$PostgreSQL::Test::Utils::timeout_default",
-		'--dry-run', '--pgdata',
-		$node_s->data_dir, '--publisher-server',
-		$node_p->connstr($db1), '--socketdir',
-		$node_s->host, '--subscriber-port',
-		$node_s->port, '--publication',
-		'pub1', '--publication',
-		'pub2', '--subscription',
-		'sub1', '--subscription',
-		'sub2', '--database',
-		$db1, '--database',
-		$db2
+		'--verbose', '--recovery-timeout',
+		"$PostgreSQL::Test::Utils::timeout_default", '--dry-run',
+		'--pgdata', $node_s->data_dir,
+		'--publisher-server', $node_p->connstr($db1),
+		'--socketdir', $node_s->host,
+		'--subscriber-port', $node_s->port,
+		'--publication', 'pub1',
+		'--publication', 'pub2',
+		'--subscription', 'sub1',
+		'--subscription', 'sub2',
+		'--database', $db1,
+		'--database', $db2
 	],
-	'run pg_createsubscriber --dry-run on node S');
+	'Ditto above, but this time using command_ok to retain the output');
+
+# Reset 'max_slot_wal_keep_size' to default after the test
+$node_p->append_conf('postgresql.conf', 'max_slot_wal_keep_size = -1');
+$node_p->reload;
 
 # Check if node S is still a standby
 $node_s->start;
-- 
2.41.0.windows.3

From 80a8e6d61f955f94a08f7f6cb443fc44035cd45c Mon Sep 17 00:00:00 2001
From: Khanna <Shubham.Khanna@fujitsu.com>
Date: Wed, 22 Jan 2025 16:32:58 +0530
Subject: [PATCH v12] Validate-max_slot_wal_keep_size-in-pg_createsubscriber

This patch introduces validation for the 'max_slot_wal_keep_size' GUC in the
'pg_createsubscriber' utility. The utility now checks that the publisher's
'max_slot_wal_keep_size' is set to '-1' during subscription creation.
This ensures proper functioning of logical replication slots.

The 'pg_createsubscriber' utility is updated to fetch and validate the
'max_slot_wal_keep_size' setting from the publisher. A warning is raised during
the '--dry-run' mode if the configuration is set to a non-default value.

This patch logs a warning if 'max_slot_wal_keep_size' is not set to '-1',
highlighting a potential risk of required WAL files being deleted on the
publisher, which could disrupt logical replication.
A test case has been added to validate correct warning reporting
when 'max_slot_wal_keep_size' is misconfigured.
---
 doc/src/sgml/ref/pg_createsubscriber.sgml     |  7 ++
 src/bin/pg_basebackup/pg_createsubscriber.c   | 20 +++++-
 .../t/040_pg_createsubscriber.pl              | 67 ++++++++++++++-----
 3 files changed, 77 insertions(+), 17 deletions(-)

diff --git a/doc/src/sgml/ref/pg_createsubscriber.sgml b/doc/src/sgml/ref/pg_createsubscriber.sgml
index 26b8e64a4e..d56487fe2c 100644
--- a/doc/src/sgml/ref/pg_createsubscriber.sgml
+++ b/doc/src/sgml/ref/pg_createsubscriber.sgml
@@ -377,6 +377,13 @@ PostgreSQL documentation
     server.  If the target server has a standby, replication will break and a
     fresh standby should be created.
    </para>
+
+   <para>
+    Replication failures can occur if required WAL files are missing. To prevent
+    this, the source server must set
+    <xref linkend="guc-max-slot-wal-keep-size"/> to <literal>-1</literal> to
+    ensure that required WAL files are not prematurely removed.
+   </para>
   </refsect2>
 
   <refsect2>
diff --git a/src/bin/pg_basebackup/pg_createsubscriber.c b/src/bin/pg_basebackup/pg_createsubscriber.c
index faf18ccf13..7433c7ae2a 100644
--- a/src/bin/pg_basebackup/pg_createsubscriber.c
+++ b/src/bin/pg_basebackup/pg_createsubscriber.c
@@ -849,6 +849,7 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 	int			max_walsenders;
 	int			cur_walsenders;
 	int			max_prepared_transactions;
+	char	   *max_slot_wal_keep_size;
 
 	pg_log_info("checking settings on publisher");
 
@@ -872,6 +873,7 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 	 * - wal_level = logical
 	 * - max_replication_slots >= current + number of dbs to be converted
 	 * - max_wal_senders >= current + number of dbs to be converted
+	 * - max_slot_wal_keep_size = -1 (to prevent deletion of required WAL files)
 	 * -----------------------------------------------------------------------
 	 */
 	res = PQexec(conn,
@@ -880,7 +882,8 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 				 " (SELECT count(*) FROM pg_catalog.pg_replication_slots),"
 				 " pg_catalog.current_setting('max_wal_senders'),"
 				 " (SELECT count(*) FROM pg_catalog.pg_stat_activity WHERE backend_type = 'walsender'),"
-				 " pg_catalog.current_setting('max_prepared_transactions')");
+				 " pg_catalog.current_setting('max_prepared_transactions'),"
+				 " pg_catalog.current_setting('max_slot_wal_keep_size')");
 
 	if (PQresultStatus(res) != PGRES_TUPLES_OK)
 	{
@@ -895,6 +898,7 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 	max_walsenders = atoi(PQgetvalue(res, 0, 3));
 	cur_walsenders = atoi(PQgetvalue(res, 0, 4));
 	max_prepared_transactions = atoi(PQgetvalue(res, 0, 5));
+	max_slot_wal_keep_size = pg_strdup(PQgetvalue(res, 0, 6));
 
 	PQclear(res);
 
@@ -905,6 +909,8 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 	pg_log_debug("publisher: current wal senders: %d", cur_walsenders);
 	pg_log_debug("publisher: max_prepared_transactions: %d",
 				 max_prepared_transactions);
+	pg_log_debug("publisher: max_slot_wal_keep_size: %s",
+				 max_slot_wal_keep_size);
 
 	disconnect_database(conn, false);
 
@@ -939,6 +945,18 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 							  "Prepared transactions will be replicated at COMMIT PREPARED.");
 	}
 
+	/*
+	 * Validate 'max_slot_wal_keep_size'. If this parameter is set to a
+	 * non-default value, it may cause replication failures due to required
+	 * WAL files being prematurely removed.
+	 */
+	if (dry_run && (strcmp(max_slot_wal_keep_size, "-1") != 0))
+	{
+		pg_log_warning("publisher requires WAL size must not be restricted");
+		pg_log_warning_hint("Set the configuration parameter \"%s\" to -1 to ensure that required WAL files are not prematurely removed.",
+							"max_slot_wal_keep_size");
+	}
+
 	pg_free(wal_level);
 
 	if (failed)
diff --git a/src/bin/pg_basebackup/t/040_pg_createsubscriber.pl b/src/bin/pg_basebackup/t/040_pg_createsubscriber.pl
index c8dbdb7e9b..c52ae8a40a 100644
--- a/src/bin/pg_basebackup/t/040_pg_createsubscriber.pl
+++ b/src/bin/pg_basebackup/t/040_pg_createsubscriber.pl
@@ -331,25 +331,60 @@ $node_p->safe_psql($db1,
 $node_p->wait_for_replay_catchup($node_s);
 $node_s->stop;
 
-# dry run mode on node S
+# Configure 'max_slot_wal_keep_size = 10MB' on the publisher and
+# reload configuration
+$node_p->append_conf('postgresql.conf', 'max_slot_wal_keep_size = 10MB');
+$node_p->reload;
+
+# dry run mode on node S and verify the warning message for misconfigured
+# 'max_slot_wal_keep_size'
+command_checks_all(
+	[
+		'pg_createsubscriber', '--verbose',
+		'--verbose', '--recovery-timeout',
+		"$PostgreSQL::Test::Utils::timeout_default", '--dry-run',
+		'--pgdata', $node_s->data_dir,
+		'--publisher-server', $node_p->connstr($db1),
+		'--socketdir', $node_s->host,
+		'--subscriber-port', $node_s->port,
+		'--publication', 'pub1',
+		'--publication', 'pub2',
+		'--subscription', 'sub1',
+		'--subscription', 'sub2',
+		'--database', $db1,
+		'--database', $db2
+	],
+	0,
+	[qr/./],
+	[
+		qr/pg_createsubscriber: warning: publisher requires WAL size must not be restricted/,
+		qr/Set the configuration parameter "max_slot_wal_keep_size" to -1 to ensure that required WAL files are not prematurely removed./,
+	],
+	'Validate warning for misconfigured max_slot_wal_keep_size on the publisher'
+);
+
+# And, same again to see the output...
 command_ok(
 	[
-		'pg_createsubscriber',
-		'--verbose',
-		'--dry-run',
-		'--recovery-timeout' => $PostgreSQL::Test::Utils::timeout_default,
-		'--pgdata' => $node_s->data_dir,
-		'--publisher-server' => $node_p->connstr($db1),
-		'--socketdir' => $node_s->host,
-		'--subscriber-port' => $node_s->port,
-		'--publication' => 'pub1',
-		'--publication' => 'pub2',
-		'--subscription' => 'sub1',
-		'--subscription' => 'sub2',
-		'--database' => $db1,
-		'--database' => $db2,
+		'pg_createsubscriber', '--verbose',
+		'--verbose', '--recovery-timeout',
+		"$PostgreSQL::Test::Utils::timeout_default", '--dry-run',
+		'--pgdata', $node_s->data_dir,
+		'--publisher-server', $node_p->connstr($db1),
+		'--socketdir', $node_s->host,
+		'--subscriber-port', $node_s->port,
+		'--publication', 'pub1',
+		'--publication', 'pub2',
+		'--subscription', 'sub1',
+		'--subscription', 'sub2',
+		'--database', $db1,
+		'--database', $db2
 	],
-	'run pg_createsubscriber --dry-run on node S');
+	'Ditto above, but this time using command_ok to retain the output');
+
+# Reset 'max_slot_wal_keep_size' to default after the test
+$node_p->append_conf('postgresql.conf', 'max_slot_wal_keep_size = -1');
+$node_p->reload;
 
 # Check if node S is still a standby
 $node_s->start;
-- 
2.41.0.windows.3

From 1b79a607d8ecd8d46e2f2be45da2a2d1d0976236 Mon Sep 17 00:00:00 2001
From: Khanna <Shubham.Khanna@fujitsu.com>
Date: Wed, 22 Jan 2025 16:32:58 +0530
Subject: [PATCH v13] Validate-max_slot_wal_keep_size-in-pg_createsubscriber

This patch introduces validation for the 'max_slot_wal_keep_size' GUC in the
'pg_createsubscriber' utility. The utility now checks that the publisher's
'max_slot_wal_keep_size' is set to '-1' during subscription creation.
This ensures proper functioning of logical replication slots.

The 'pg_createsubscriber' utility is updated to fetch and validate the
'max_slot_wal_keep_size' setting from the publisher. A warning is raised during
the '--dry-run' mode if the configuration is set to a non-default value.

This patch logs a warning if 'max_slot_wal_keep_size' is not set to '-1',
highlighting a potential risk of required WAL files being deleted on the
publisher, which could disrupt logical replication.
A test case has been added to validate correct warning reporting
when 'max_slot_wal_keep_size' is misconfigured.
---
 doc/src/sgml/ref/pg_createsubscriber.sgml     |  7 +++
 src/bin/pg_basebackup/pg_createsubscriber.c   | 20 ++++++++-
 .../t/040_pg_createsubscriber.pl              | 44 +++++++++++++++++--
 3 files changed, 67 insertions(+), 4 deletions(-)

diff --git a/doc/src/sgml/ref/pg_createsubscriber.sgml b/doc/src/sgml/ref/pg_createsubscriber.sgml
index 26b8e64a4e..d56487fe2c 100644
--- a/doc/src/sgml/ref/pg_createsubscriber.sgml
+++ b/doc/src/sgml/ref/pg_createsubscriber.sgml
@@ -377,6 +377,13 @@ PostgreSQL documentation
     server.  If the target server has a standby, replication will break and a
     fresh standby should be created.
    </para>
+
+   <para>
+    Replication failures can occur if required WAL files are missing. To prevent
+    this, the source server must set
+    <xref linkend="guc-max-slot-wal-keep-size"/> to <literal>-1</literal> to
+    ensure that required WAL files are not prematurely removed.
+   </para>
   </refsect2>
 
   <refsect2>
diff --git a/src/bin/pg_basebackup/pg_createsubscriber.c b/src/bin/pg_basebackup/pg_createsubscriber.c
index faf18ccf13..7433c7ae2a 100644
--- a/src/bin/pg_basebackup/pg_createsubscriber.c
+++ b/src/bin/pg_basebackup/pg_createsubscriber.c
@@ -849,6 +849,7 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 	int			max_walsenders;
 	int			cur_walsenders;
 	int			max_prepared_transactions;
+	char	   *max_slot_wal_keep_size;
 
 	pg_log_info("checking settings on publisher");
 
@@ -872,6 +873,7 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 	 * - wal_level = logical
 	 * - max_replication_slots >= current + number of dbs to be converted
 	 * - max_wal_senders >= current + number of dbs to be converted
+	 * - max_slot_wal_keep_size = -1 (to prevent deletion of required WAL files)
 	 * -----------------------------------------------------------------------
 	 */
 	res = PQexec(conn,
@@ -880,7 +882,8 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 				 " (SELECT count(*) FROM pg_catalog.pg_replication_slots),"
 				 " pg_catalog.current_setting('max_wal_senders'),"
 				 " (SELECT count(*) FROM pg_catalog.pg_stat_activity WHERE backend_type = 'walsender'),"
-				 " pg_catalog.current_setting('max_prepared_transactions')");
+				 " pg_catalog.current_setting('max_prepared_transactions'),"
+				 " pg_catalog.current_setting('max_slot_wal_keep_size')");
 
 	if (PQresultStatus(res) != PGRES_TUPLES_OK)
 	{
@@ -895,6 +898,7 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 	max_walsenders = atoi(PQgetvalue(res, 0, 3));
 	cur_walsenders = atoi(PQgetvalue(res, 0, 4));
 	max_prepared_transactions = atoi(PQgetvalue(res, 0, 5));
+	max_slot_wal_keep_size = pg_strdup(PQgetvalue(res, 0, 6));
 
 	PQclear(res);
 
@@ -905,6 +909,8 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 	pg_log_debug("publisher: current wal senders: %d", cur_walsenders);
 	pg_log_debug("publisher: max_prepared_transactions: %d",
 				 max_prepared_transactions);
+	pg_log_debug("publisher: max_slot_wal_keep_size: %s",
+				 max_slot_wal_keep_size);
 
 	disconnect_database(conn, false);
 
@@ -939,6 +945,18 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 							  "Prepared transactions will be replicated at COMMIT PREPARED.");
 	}
 
+	/*
+	 * Validate 'max_slot_wal_keep_size'. If this parameter is set to a
+	 * non-default value, it may cause replication failures due to required
+	 * WAL files being prematurely removed.
+	 */
+	if (dry_run && (strcmp(max_slot_wal_keep_size, "-1") != 0))
+	{
+		pg_log_warning("publisher requires WAL size must not be restricted");
+		pg_log_warning_hint("Set the configuration parameter \"%s\" to -1 to ensure that required WAL files are not prematurely removed.",
+							"max_slot_wal_keep_size");
+	}
+
 	pg_free(wal_level);
 
 	if (failed)
diff --git a/src/bin/pg_basebackup/t/040_pg_createsubscriber.pl b/src/bin/pg_basebackup/t/040_pg_createsubscriber.pl
index c8dbdb7e9b..5cb9b6c590 100644
--- a/src/bin/pg_basebackup/t/040_pg_createsubscriber.pl
+++ b/src/bin/pg_basebackup/t/040_pg_createsubscriber.pl
@@ -331,11 +331,45 @@ $node_p->safe_psql($db1,
 $node_p->wait_for_replay_catchup($node_s);
 $node_s->stop;
 
-# dry run mode on node S
+# Configure 'max_slot_wal_keep_size = 10MB' on the publisher and
+# reload configuration
+$node_p->append_conf('postgresql.conf', 'max_slot_wal_keep_size = 10MB');
+$node_p->reload;
+
+# dry run mode on node S and verify the warning message for misconfigured
+# 'max_slot_wal_keep_size'
+command_checks_all(
+	[
+		'pg_createsubscriber',
+		'--dry-run',
+		'--recovery-timeout' => $PostgreSQL::Test::Utils::timeout_default,
+		'--pgdata' => $node_s->data_dir,
+		'--publisher-server' => $node_p->connstr($db1),
+		'--socketdir' => $node_s->host,
+		'--subscriber-port' => $node_s->port,
+		'--publication' => 'pub1',
+		'--publication' => 'pub2',
+		'--subscription' => 'sub1',
+		'--subscription' => 'sub2',
+		'--database' => $db1,
+		'--database' => $db2,
+	],
+	0,
+	[qr/./],
+	[
+		qr/pg_createsubscriber: warning: publisher requires WAL size must not be restricted/,
+		qr/Set the configuration parameter "max_slot_wal_keep_size" to -1 to ensure that required WAL files are not prematurely removed./,
+	],
+	'Validate warning for misconfigured max_slot_wal_keep_size on the publisher'
+);
+
+# Execute the same command again but this time use 'command_ok' so
+# that the log files can be inspected.  --verbose is used twice
+# to show more information.
 command_ok(
 	[
 		'pg_createsubscriber',
-		'--verbose',
+		'--verbose', '--verbose',
 		'--dry-run',
 		'--recovery-timeout' => $PostgreSQL::Test::Utils::timeout_default,
 		'--pgdata' => $node_s->data_dir,
@@ -349,7 +383,11 @@ command_ok(
 		'--database' => $db1,
 		'--database' => $db2,
 	],
-	'run pg_createsubscriber --dry-run on node S');
+	'Ditto above, but this time using command_ok to retain the output');
+
+# Reset 'max_slot_wal_keep_size' to default after the test
+$node_p->append_conf('postgresql.conf', 'max_slot_wal_keep_size = -1');
+$node_p->reload;
 
 # Check if node S is still a standby
 $node_s->start;
-- 
2.41.0.windows.3

From acac447e5c74598dc6b201be466c426e26a29436 Mon Sep 17 00:00:00 2001
From: Khanna <Shubham.Khanna@fujitsu.com>
Date: Wed, 22 Jan 2025 16:32:58 +0530
Subject: [PATCH v14] Validate-max_slot_wal_keep_size-in-pg_createsubscriber

This patch introduces validation for the 'max_slot_wal_keep_size' GUC in the
'pg_createsubscriber' utility. The utility now checks that the publisher's
'max_slot_wal_keep_size' is set to '-1' during subscription creation.
This ensures proper functioning of logical replication slots.

The 'pg_createsubscriber' utility is updated to fetch and validate the
'max_slot_wal_keep_size' setting from the publisher. A warning is raised during
the '--dry-run' mode if the configuration is set to a non-default value.

This patch logs a warning if 'max_slot_wal_keep_size' is not set to '-1',
highlighting a potential risk of required WAL files being deleted on the
publisher, which could disrupt logical replication.
A test case has been added to validate correct warning reporting
when 'max_slot_wal_keep_size' is misconfigured.
---
 doc/src/sgml/ref/pg_createsubscriber.sgml   |  7 +++++++
 src/bin/pg_basebackup/pg_createsubscriber.c | 20 +++++++++++++++++++-
 2 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/doc/src/sgml/ref/pg_createsubscriber.sgml b/doc/src/sgml/ref/pg_createsubscriber.sgml
index 26b8e64a4e0..d56487fe2ca 100644
--- a/doc/src/sgml/ref/pg_createsubscriber.sgml
+++ b/doc/src/sgml/ref/pg_createsubscriber.sgml
@@ -377,6 +377,13 @@ PostgreSQL documentation
     server.  If the target server has a standby, replication will break and a
     fresh standby should be created.
    </para>
+
+   <para>
+    Replication failures can occur if required WAL files are missing. To prevent
+    this, the source server must set
+    <xref linkend="guc-max-slot-wal-keep-size"/> to <literal>-1</literal> to
+    ensure that required WAL files are not prematurely removed.
+   </para>
   </refsect2>
 
   <refsect2>
diff --git a/src/bin/pg_basebackup/pg_createsubscriber.c b/src/bin/pg_basebackup/pg_createsubscriber.c
index 2d881d54f5b..3fe5157fcd1 100644
--- a/src/bin/pg_basebackup/pg_createsubscriber.c
+++ b/src/bin/pg_basebackup/pg_createsubscriber.c
@@ -849,6 +849,7 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 	int			max_walsenders;
 	int			cur_walsenders;
 	int			max_prepared_transactions;
+	char	   *max_slot_wal_keep_size;
 
 	pg_log_info("checking settings on publisher");
 
@@ -872,6 +873,7 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 	 * - wal_level = logical
 	 * - max_replication_slots >= current + number of dbs to be converted
 	 * - max_wal_senders >= current + number of dbs to be converted
+	 * - max_slot_wal_keep_size = -1 (to prevent deletion of required WAL files)
 	 * -----------------------------------------------------------------------
 	 */
 	res = PQexec(conn,
@@ -880,7 +882,8 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 				 " (SELECT count(*) FROM pg_catalog.pg_replication_slots),"
 				 " pg_catalog.current_setting('max_wal_senders'),"
 				 " (SELECT count(*) FROM pg_catalog.pg_stat_activity WHERE backend_type = 'walsender'),"
-				 " pg_catalog.current_setting('max_prepared_transactions')");
+				 " pg_catalog.current_setting('max_prepared_transactions'),"
+				 " pg_catalog.current_setting('max_slot_wal_keep_size')");
 
 	if (PQresultStatus(res) != PGRES_TUPLES_OK)
 	{
@@ -895,6 +898,7 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 	max_walsenders = atoi(PQgetvalue(res, 0, 3));
 	cur_walsenders = atoi(PQgetvalue(res, 0, 4));
 	max_prepared_transactions = atoi(PQgetvalue(res, 0, 5));
+	max_slot_wal_keep_size = pg_strdup(PQgetvalue(res, 0, 6));
 
 	PQclear(res);
 
@@ -905,6 +909,8 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 	pg_log_debug("publisher: current wal senders: %d", cur_walsenders);
 	pg_log_debug("publisher: max_prepared_transactions: %d",
 				 max_prepared_transactions);
+	pg_log_debug("publisher: max_slot_wal_keep_size: %s",
+				 max_slot_wal_keep_size);
 
 	disconnect_database(conn, false);
 
@@ -939,6 +945,18 @@ check_publisher(const struct LogicalRepInfo *dbinfo)
 							  "Prepared transactions will be replicated at COMMIT PREPARED.");
 	}
 
+	/*
+	 * Validate 'max_slot_wal_keep_size'. If this parameter is set to a
+	 * non-default value, it may cause replication failures due to required
+	 * WAL files being prematurely removed.
+	 */
+	if (dry_run && (strcmp(max_slot_wal_keep_size, "-1") != 0))
+	{
+		pg_log_warning("publisher requires WAL size must not be restricted");
+		pg_log_warning_hint("Set the configuration parameter \"%s\" to -1 to ensure that required WAL files are not prematurely removed.",
+							"max_slot_wal_keep_size");
+	}
+
 	pg_free(wal_level);
 
 	if (failed)
-- 
2.41.0.windows.3