From 4ca115725de20ed1b1bb45ceb27b1de28739af70 Mon Sep 17 00:00:00 2001 From: Ants Aasma Date: Sun, 2 Aug 2026 11:53:23 +0200 Subject: [PATCH v5] Checkpoint replication slots later in the checkpoint cycle MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Previously, CheckPointReplicationSlots() ran at the start of CheckPointGuts(), while WAL cleanup occurred much later in CreateCheckPoint() and CreateRestartPoint(), after the buffer write and ProcessSyncRequests() phases. During a spread checkpoint, this gap could be several minutes. During that time, active replication slots could advance their restart_lsn. However, replicationSlotMinLSN had already been computed from the older saved values. As a result, KeepLogSeg() could retain WAL segments that were no longer needed, causing unnecessary pg_wal growth until the next checkpoint or restartpoint. Fix this by moving CheckPointReplicationSlots(), CheckPointSnapBuild(), and CheckPointLogicalRewriteHeap() to just before CheckPointTwoPhase(), after the buffer write and ProcessSyncRequests() phases. This makes WAL retention decisions use the latest replication slot state. The logical snapshot and rewrite heap cleanup decisions also benefit from the updated saved restart_lsn. Author: Ants Aasma Author: Hüseyin Demir Reviewed-by: Fujii Masao Discussion: https://postgr.es/m/CANwKhkPCBcTQ_pk06MD5W5YYNnuYHp8dLNuOUz8-5pMBMPY1Bw%40mail.gmail.com --- src/backend/access/transam/xlog.c | 15 +++++++++++---- 1 file changed, 11 insertions(+), 4 deletions(-) diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f8b939853e9..b23d8bbbdad 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -8049,9 +8049,6 @@ static void CheckPointGuts(XLogRecPtr checkPointRedo, int flags) { CheckPointRelationMap(); - CheckPointReplicationSlots(flags & CHECKPOINT_IS_SHUTDOWN); - CheckPointSnapBuild(); - CheckPointLogicalRewriteHeap(); CheckPointReplicationOrigin(); /* Write out all dirty data in SLRUs and the main buffer pool */ @@ -8071,7 +8068,17 @@ 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 */ + /* + * Run replication slot checkpointing after buffer writes and + * ProcessSyncRequests(), so WAL removal uses a fresher slot retention + * horizon and avoids retaining WAL segments that slots no longer need. + * Then clean up logical snapshots and rewrite mappings based on the + * updated saved restart LSNs. Also delay 2PC checkpointing as long as + * possible. + */ + CheckPointReplicationSlots(flags & CHECKPOINT_IS_SHUTDOWN); + CheckPointSnapBuild(); + CheckPointLogicalRewriteHeap(); CheckPointTwoPhase(checkPointRedo); } -- 2.55.0