Fix the handling of two GUCs during upgrade.

Previously, the check_hook functions for max_slot_wal_keep_size and
idle_replication_slot_timeout would incorrectly raise an ERROR for values
set in postgresql.conf during upgrade, even though those values were not
actively used in the upgrade process.

To prevent logical slot invalidation during upgrade, we used to set
special values for these GUCs. Now, instead of relying on those values, we
directly prevent WAL removal and logical slot invalidation caused by
max_slot_wal_keep_size and idle_replication_slot_timeout.

Note: PostgreSQL 17 does not include the idle_replication_slot_timeout
GUC, so related changes were not backported.

BUG #18979
Reported-by: jorsol <jorsol@gmail.com>
Author: Dilip Kumar <dilipbalaut@gmail.com>
Reviewed by: vignesh C <vignesh21@gmail.com>
Reviewed by: Alvaro Herrera <alvherre@alvh.no-ip.org>
Backpatch-through: 17, where it was introduced
Discussion: https://postgr.es/m/219561.1751826409@sss.pgh.pa.us
Discussion: https://postgr.es/m/18979-a1b7fdbb7cd181c6@postgresql.org

1 files changed, 8 insertions, 25 deletions

diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index a8cc6402d62..304b60933c9 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -2347,25 +2347,6 @@ check_wal_segment_size(int *newval, void **extra, GucSource source)
 }
 
 /*
- * 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.
  */
@@ -8150,17 +8131,19 @@ KeepLogSeg(XLogRecPtr recptr, XLogSegNo *logSegNo)
 	XLByteToSeg(recptr, currSegNo, wal_segment_size);
 	segno = currSegNo;
 
-	/*
-	 * Calculate how many segments are kept by slots first, adjusting for
-	 * max_slot_wal_keep_size.
-	 */
+	/* Calculate how many segments are kept by slots. */
 	keep = XLogGetReplicationSlotMinimumLSN();
 	if (keep != InvalidXLogRecPtr && keep < recptr)
 	{
 		XLByteToSeg(keep, segno, wal_segment_size);
 
-		/* Cap by max_slot_wal_keep_size ... */
-		if (max_slot_wal_keep_size_mb >= 0)
+		/*
+		 * Account for max_slot_wal_keep_size to avoid keeping more than
+		 * configured.  However, don't do that during a binary upgrade: if
+		 * slots were to be invalidated because of this, it would not be
+		 * possible to preserve logical ones during the upgrade.
+		 */
+		if (max_slot_wal_keep_size_mb >= 0 && !IsBinaryUpgrade)
 		{
 			uint64		slot_keep_segs;