0001-Checkpoint-replication-slots-late-in-the-cycle.patch

From 2878337eb8399c8c5a440b110ce6da4b318acc8c Mon Sep 17 00:00:00 2001
From: Ants Aasma <ants@cybertec.at>
Date: Thu, 7 May 2026 13:13:47 +0300
Subject: [PATCH] Checkpoint replication slots late in the cycle

Syncing replication slots computes XLogCtl->replicationSlotMinLSN which
is used to decide how much WAL to retain. Currently this happens at the
start of the checkpoint cycle, whereas WAL cleanup happens at the end.
For spread checkpoints the information might be considerably stale and
we hold onto too much WAL. Postponing the replication slot sync to the
end of checkpoint makes WAL cleanup use much more recent information.
---
 src/backend/access/transam/xlog.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index f0434da40c9..6e6f411f47f 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -8046,7 +8046,6 @@ static void
 CheckPointGuts(XLogRecPtr checkPointRedo, int flags)
 {
 	CheckPointRelationMap();
-	CheckPointReplicationSlots(flags & CHECKPOINT_IS_SHUTDOWN);
 	CheckPointSnapBuild();
 	CheckPointLogicalRewriteHeap();
 	CheckPointReplicationOrigin();
@@ -8068,7 +8067,11 @@ CheckPointGuts(XLogRecPtr checkPointRedo, int flags)
 	CheckpointStats.ckpt_sync_end_t = GetCurrentTimestamp();
 	TRACE_POSTGRESQL_BUFFER_CHECKPOINT_DONE();
 
-	/* We deliberately delay 2PC checkpointing as long as possible */
+	/*
+	 * We deliberately delay checkpointing of replication slots and 2PC for
+	 * as long as possible.
+	 */
+	CheckPointReplicationSlots(flags & CHECKPOINT_IS_SHUTDOWN);
 	CheckPointTwoPhase(checkPointRedo);
 }
 
-- 
2.51.0