On Tue, Feb 15, 2022 at 10:14:04PM -0800, Nathan Bossart wrote:
> It looks like register_unlink_segment() is called prior to the checkpoint,
> but the checkpointer is not calling RememberSyncRequest() until after
> SyncPreCheckpoint(). This means that the requests are registered with the
> next checkpoint cycle count, so they aren't processed until the next
> checkpoint.
Calling AbsorbSyncRequests() before advancing the checkpoint cycle counter
seems to fix the issue. However, this requires moving SyncPreCheckpoint()
out of the critical section in CreateCheckPoint(). Patch attached.
--
Nathan Bossart
Amazon Web Services: https://aws.amazon.com
>From 188fbe8ab12387c423081edfb85b26e43b342f4e Mon Sep 17 00:00:00 2001
From: Nathan Bossart <nathandboss...@gmail.com>
Date: Tue, 15 Feb 2022 22:53:04 -0800
Subject: [PATCH v1 1/1] call AbsorbSyncRequests() before advancing checkpoint
cycle counter
---
src/backend/access/transam/xlog.c | 14 +++++++-------
src/backend/storage/sync/sync.c | 6 ++++++
2 files changed, 13 insertions(+), 7 deletions(-)
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 60d0f3d99e..c72d6faa88 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -9042,6 +9042,13 @@ CreateCheckPoint(int flags)
MemSet(&CheckpointStats, 0, sizeof(CheckpointStats));
CheckpointStats.ckpt_start_t = GetCurrentTimestamp();
+ /*
+ * Let smgr prepare for checkpoint; this has to happen before we determine
+ * the REDO pointer. Note that smgr must not do anything that'd have to
+ * be undone if we decide no checkpoint is needed.
+ */
+ SyncPreCheckpoint();
+
/*
* Use a critical section to force system panic if we have trouble.
*/
@@ -9055,13 +9062,6 @@ CreateCheckPoint(int flags)
LWLockRelease(ControlFileLock);
}
- /*
- * Let smgr prepare for checkpoint; this has to happen before we determine
- * the REDO pointer. Note that smgr must not do anything that'd have to
- * be undone if we decide no checkpoint is needed.
- */
- SyncPreCheckpoint();
-
/* Begin filling in the checkpoint WAL record */
MemSet(&checkPoint, 0, sizeof(checkPoint));
checkPoint.time = (pg_time_t) time(NULL);
diff --git a/src/backend/storage/sync/sync.c b/src/backend/storage/sync/sync.c
index 543f691f2d..8ffb3b8279 100644
--- a/src/backend/storage/sync/sync.c
+++ b/src/backend/storage/sync/sync.c
@@ -180,6 +180,12 @@ InitSync(void)
void
SyncPreCheckpoint(void)
{
+ /*
+ * Some operations assume that the next checkpoint will process recently
+ * forwarded requests, so absorb them before we advance the cycle counter.
+ */
+ AbsorbSyncRequests();
+
/*
* Any unlink requests arriving after this point will be assigned the next
* cycle counter, and won't be unlinked until next checkpoint.
--
2.25.1
