From 8bfb231b43d7f6058041483f2b823dd52eac7bf8 Mon Sep 17 00:00:00 2001
From: Amit Kapila <akapila@postgresql.org>
Date: Fri, 10 Nov 2023 08:45:01 +0530
Subject: [PATCH] Prohibit max_slot_wal_keep_size to value other than -1 during
 upgrade.

We don't want existing slots in the old cluster to get invalidated during
the upgrade. During an upgrade, we set this variable to -1 via the command
line in an attempt to prevent such invalidations, but users have ways to
override it. This patch ensures the value is not overridden by the user.

Author: Kyotaro Horiguchi
Reviewed-by: Peter Smith, Alvaro Herrera
Discussion: http://postgr.es/m/20231027.115759.2206827438943188717.horikyota.ntt@gmail.com
---
 src/backend/access/transam/xlog.c   | 19 +++++++++++++++++++
 src/backend/replication/slot.c      | 16 +++++-----------
 src/backend/utils/misc/guc_tables.c |  2 +-
 src/include/utils/guc_hooks.h       |  2 ++
 4 files changed, 27 insertions(+), 12 deletions(-)

diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b541be8eec..1159dff1a6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -2063,6 +2063,25 @@ check_wal_segment_size(int *newval, void **extra, GucSource source)
 	return true;
 }
 
+/*
+ * GUC check_hook for max_slot_wal_keep_size
+ *
+ * We don't allow the value of max_slot_wal_keep_size other than -1 during the
+ * binary upgrade. See start_postmaster() in pg_upgrade for more details.
+ */
+bool
+check_max_slot_wal_keep_size(int *newval, void **extra, GucSource source)
+{
+	if (IsBinaryUpgrade && *newval != -1)
+	{
+		GUC_check_errdetail("\"%s\" must be set to -1 during binary upgrade mode.",
+							"max_slot_wal_keep_size");
+		return false;
+	}
+
+	return true;
+}
+
 /*
  * At a checkpoint, how many WAL segments to recycle as preallocated future
  * XLOG segments? Returns the highest segment that should be preallocated.
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 99823df3c7..781aa43cc4 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1424,18 +1424,12 @@ InvalidatePossiblyObsoleteSlot(ReplicationSlotInvalidationCause cause,
 		SpinLockRelease(&s->mutex);
 
 		/*
-		 * The logical replication slots shouldn't be invalidated as
-		 * max_slot_wal_keep_size GUC is set to -1 during the upgrade.
-		 *
-		 * The following is just a sanity check.
+		 * The logical replication slots shouldn't be invalidated as GUC
+		 * max_slot_wal_keep_size is set to -1 during the binary upgrade. See
+		 * check_old_cluster_for_valid_slots() where we ensure that no
+		 * invalidated before the upgrade.
 		 */
-		if (*invalidated && SlotIsLogical(s) && IsBinaryUpgrade)
-		{
-			ereport(ERROR,
-					errcode(ERRCODE_INVALID_PARAMETER_VALUE),
-					errmsg("replication slots must not be invalidated during the upgrade"),
-					errhint("\"max_slot_wal_keep_size\" must be set to -1 during the upgrade"));
-		}
+		Assert(!(*invalidated && SlotIsLogical(s) && IsBinaryUpgrade));
 
 		if (active_pid != 0)
 		{
diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c
index beed72abbd..b764ef6998 100644
--- a/src/backend/utils/misc/guc_tables.c
+++ b/src/backend/utils/misc/guc_tables.c
@@ -2845,7 +2845,7 @@ struct config_int ConfigureNamesInt[] =
 		},
 		&max_slot_wal_keep_size_mb,
 		-1, -1, MAX_KILOBYTES,
-		NULL, NULL, NULL
+		check_max_slot_wal_keep_size, NULL, NULL
 	},
 
 	{
diff --git a/src/include/utils/guc_hooks.h b/src/include/utils/guc_hooks.h
index 2a191830a8..3d74483f44 100644
--- a/src/include/utils/guc_hooks.h
+++ b/src/include/utils/guc_hooks.h
@@ -84,6 +84,8 @@ extern bool check_maintenance_io_concurrency(int *newval, void **extra,
 extern void assign_maintenance_io_concurrency(int newval, void *extra);
 extern bool check_max_connections(int *newval, void **extra, GucSource source);
 extern bool check_max_wal_senders(int *newval, void **extra, GucSource source);
+extern bool check_max_slot_wal_keep_size(int *newval, void **extra,
+										 GucSource source);
 extern void assign_max_wal_size(int newval, void *extra);
 extern bool check_max_worker_processes(int *newval, void **extra,
 									   GucSource source);
-- 
2.39.5