v10_REL_18-0001-Remove-the-validation-from-the-GUC-check-.txt

From cb305a8bd8f96a7b95083d6423c6bc77fe21238e Mon Sep 17 00:00:00 2001
From: Shlok Kyal <shlok.kyal.oss@gmail.com>
Date: Wed, 10 Sep 2025 15:08:23 +0530
Subject: [PATCH v10_REL_18] Remove the validation from the GUC check hook and
 add parsing check

The validation in check_synchronized_standby_slots cannot be run
in postmaster and hence can result inconsistent values in some
backends that inherit the value from postmaster and those
that are started newly. Also, this validation results in parallel
workers fail to with error. This causes all the commands run by
parallel workers to fail, which seems unnecesary. This validation
already happens in StandbySlotsHaveCaughtup() where this GUC is
used, so it can be removed from the GUC check. Also added a
parsing check for the slot names specified in this GUC.
---
 src/backend/replication/slot.c                | 59 +++++--------------
 .../unsafe_tests/expected/guc_privs.out       | 10 ++++
 .../modules/unsafe_tests/sql/guc_privs.sql    |  8 +++
 3 files changed, 34 insertions(+), 43 deletions(-)

diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index ac910f6a74a..101157ed8c9 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -2743,53 +2743,32 @@ GetSlotInvalidationCauseName(ReplicationSlotInvalidationCause cause)
 static bool
 validate_sync_standby_slots(char *rawname, List **elemlist)
 {
-	bool		ok;
-
 	/* Verify syntax and parse string into a list of identifiers */
-	ok = SplitIdentifierString(rawname, ',', elemlist);
-
-	if (!ok)
+	if (!SplitIdentifierString(rawname, ',', elemlist))
 	{
 		GUC_check_errdetail("List syntax is invalid.");
+		return false;
 	}
-	else if (MyProc)
+
+	/* Iterate the list to validate each slot name */
+	foreach_ptr(char, name, *elemlist)
 	{
-		/*
-		 * Check that each specified slot exist and is physical.
-		 *
-		 * Because we need an LWLock, we cannot do this on processes without a
-		 * PGPROC, so we skip it there; but see comments in
-		 * StandbySlotsHaveCaughtup() as to why that's not a problem.
-		 */
-		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
+		int			err_code;
+		char	   *err_msg = NULL;
+		char	   *err_hint = NULL;
 
-		foreach_ptr(char, name, *elemlist)
+		if (!ReplicationSlotValidateNameInternal(name, &err_code, &err_msg,
+												 &err_hint))
 		{
-			ReplicationSlot *slot;
-
-			slot = SearchNamedReplicationSlot(name, false);
-
-			if (!slot)
-			{
-				GUC_check_errdetail("Replication slot \"%s\" does not exist.",
-									name);
-				ok = false;
-				break;
-			}
-
-			if (!SlotIsPhysical(slot))
-			{
-				GUC_check_errdetail("\"%s\" is not a physical replication slot.",
-									name);
-				ok = false;
-				break;
-			}
+			GUC_check_errcode(err_code);
+			GUC_check_errdetail("%s", err_msg);
+			if (err_hint != NULL)
+				GUC_check_errhint("%s", err_hint);
+			return false;
 		}
-
-		LWLockRelease(ReplicationSlotControlLock);
 	}
 
-	return ok;
+	return true;
 }
 
 /*
@@ -2947,12 +2926,6 @@ StandbySlotsHaveCaughtup(XLogRecPtr wait_for_lsn, int elevel)
 		/*
 		 * If a slot name provided in synchronized_standby_slots does not
 		 * exist, report a message and exit the loop.
-		 *
-		 * Though validate_sync_standby_slots (the GUC check_hook) tries to
-		 * avoid this, it can nonetheless happen because the user can specify
-		 * a nonexistent slot name before server startup. That function cannot
-		 * validate such a slot during startup, as ReplicationSlotCtl is not
-		 * initialized by then.  Also, the user might have dropped one slot.
 		 */
 		if (!slot)
 		{
diff --git a/src/test/modules/unsafe_tests/expected/guc_privs.out b/src/test/modules/unsafe_tests/expected/guc_privs.out
index 6c0ad898341..7f76b675c8c 100644
--- a/src/test/modules/unsafe_tests/expected/guc_privs.out
+++ b/src/test/modules/unsafe_tests/expected/guc_privs.out
@@ -581,6 +581,16 @@ DROP ROLE regress_host_resource_newadmin;  -- ok, nothing was transferred
 -- Use "drop owned by" so we can drop the role
 DROP OWNED BY regress_host_resource_admin;  -- ok
 DROP ROLE regress_host_resource_admin;  -- ok
+-- Test for GUC synchronized standby slots
+-- Cannot set synchronized_standby_slots to an invalid slot name
+ALTER SYSTEM SET synchronized_standby_slots='invalid*';
+ERROR:  invalid value for parameter "synchronized_standby_slots": "invalid*"
+DETAIL:  replication slot name "invalid*" contains invalid character
+HINT:  Replication slot names may only contain lower case letters, numbers, and the underscore character.
+-- Can set synchronized_standby_slots to a non-existent slot name
+ALTER SYSTEM SET synchronized_standby_slots='missing';
+-- Reset the GUC
+ALTER SYSTEM RESET synchronized_standby_slots;
 -- Clean up
 RESET SESSION AUTHORIZATION;
 DROP ROLE regress_admin; -- ok
diff --git a/src/test/modules/unsafe_tests/sql/guc_privs.sql b/src/test/modules/unsafe_tests/sql/guc_privs.sql
index 9bcbbfa9040..ccbff5a5358 100644
--- a/src/test/modules/unsafe_tests/sql/guc_privs.sql
+++ b/src/test/modules/unsafe_tests/sql/guc_privs.sql
@@ -262,6 +262,14 @@ DROP ROLE regress_host_resource_newadmin;  -- ok, nothing was transferred
 DROP OWNED BY regress_host_resource_admin;  -- ok
 DROP ROLE regress_host_resource_admin;  -- ok
 
+-- Test for GUC synchronized standby slots
+-- Cannot set synchronized_standby_slots to an invalid slot name
+ALTER SYSTEM SET synchronized_standby_slots='invalid*';
+-- Can set synchronized_standby_slots to a non-existent slot name
+ALTER SYSTEM SET synchronized_standby_slots='missing';
+-- Reset the GUC
+ALTER SYSTEM RESET synchronized_standby_slots;
+
 -- Clean up
 RESET SESSION AUTHORIZATION;
 DROP ROLE regress_admin; -- ok
-- 
2.34.1