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* pgsql: Fix remaining race condition with CLOG truncation and LISTEN/NOT
@ 2025-11-12 19:16 Heikki Linnakangas <heikki.linnakangas@iki.fi>
0 siblings, 0 replies; 7+ messages in thread
From: Heikki Linnakangas @ 2025-11-12 19:16 UTC (permalink / raw)
To: pgsql-committers@lists.postgresql.org
Fix remaining race condition with CLOG truncation and LISTEN/NOTIFY
Previous commit fixed a bug where VACUUM would truncate the CLOG
that's still needed to check the commit status of XIDs in the async
notify queue, but as mentioned in the commit message, it wasn't a full
fix. If a backend is executing asyncQueueReadAllNotifications() and
has just made a local copy of an async SLRU page which contains old
XIDs, vacuum can concurrently truncate the CLOG covering those XIDs,
and the backend still gets an error when it calls
TransactionIdDidCommit() on those XIDs in the local copy. This commit
fixes that race condition.
To fix, hold the SLRU bank lock across the TransactionIdDidCommit()
calls in NOTIFY processing.
Per Tom Lane's idea. Backpatch to all supported versions.
Reviewed-by: Joel Jacobson <joel@compiler.org>
Reviewed-by: Arseniy Mukhin <arseniy.mukhin.dev@gmail.com>
Discussion: https://www.postgresql.org/message-id/2759499.1761756503@sss.pgh.pa.us
Backpatch-through: 14
Branch
------
REL_18_STABLE
Details
-------
https://git.postgresql.org/pg/commitdiff/7b069a1876e46e319690459c578750e8b532520f
Modified Files
--------------
src/backend/commands/async.c | 123 ++++++++++++++++++++++---------------------
1 file changed, 62 insertions(+), 61 deletions(-)
^ permalink raw reply [nested|flat] 7+ messages in thread
* pgsql: Fix remaining race condition with CLOG truncation and LISTEN/NOT
@ 2025-11-12 19:16 Heikki Linnakangas <heikki.linnakangas@iki.fi>
0 siblings, 0 replies; 7+ messages in thread
From: Heikki Linnakangas @ 2025-11-12 19:16 UTC (permalink / raw)
To: pgsql-committers@lists.postgresql.org
Fix remaining race condition with CLOG truncation and LISTEN/NOTIFY
Previous commit fixed a bug where VACUUM would truncate the CLOG
that's still needed to check the commit status of XIDs in the async
notify queue, but as mentioned in the commit message, it wasn't a full
fix. If a backend is executing asyncQueueReadAllNotifications() and
has just made a local copy of an async SLRU page which contains old
XIDs, vacuum can concurrently truncate the CLOG covering those XIDs,
and the backend still gets an error when it calls
TransactionIdDidCommit() on those XIDs in the local copy. This commit
fixes that race condition.
To fix, hold the SLRU bank lock across the TransactionIdDidCommit()
calls in NOTIFY processing.
Per Tom Lane's idea. Backpatch to all supported versions.
Reviewed-by: Joel Jacobson <joel@compiler.org>
Reviewed-by: Arseniy Mukhin <arseniy.mukhin.dev@gmail.com>
Discussion: https://www.postgresql.org/message-id/2759499.1761756503@sss.pgh.pa.us
Backpatch-through: 14
Branch
------
REL_14_STABLE
Details
-------
https://git.postgresql.org/pg/commitdiff/c2e58c0711fe76daef47c7e85a770fc93156b90f
Modified Files
--------------
src/backend/commands/async.c | 123 ++++++++++++++++++++++---------------------
1 file changed, 62 insertions(+), 61 deletions(-)
^ permalink raw reply [nested|flat] 7+ messages in thread
* pgsql: Fix remaining race condition with CLOG truncation and LISTEN/NOT
@ 2025-11-12 19:16 Heikki Linnakangas <heikki.linnakangas@iki.fi>
0 siblings, 1 reply; 7+ messages in thread
From: Heikki Linnakangas @ 2025-11-12 19:16 UTC (permalink / raw)
To: pgsql-committers@lists.postgresql.org
Fix remaining race condition with CLOG truncation and LISTEN/NOTIFY
Previous commit fixed a bug where VACUUM would truncate the CLOG
that's still needed to check the commit status of XIDs in the async
notify queue, but as mentioned in the commit message, it wasn't a full
fix. If a backend is executing asyncQueueReadAllNotifications() and
has just made a local copy of an async SLRU page which contains old
XIDs, vacuum can concurrently truncate the CLOG covering those XIDs,
and the backend still gets an error when it calls
TransactionIdDidCommit() on those XIDs in the local copy. This commit
fixes that race condition.
To fix, hold the SLRU bank lock across the TransactionIdDidCommit()
calls in NOTIFY processing.
Per Tom Lane's idea. Backpatch to all supported versions.
Reviewed-by: Joel Jacobson <joel@compiler.org>
Reviewed-by: Arseniy Mukhin <arseniy.mukhin.dev@gmail.com>
Discussion: https://www.postgresql.org/message-id/2759499.1761756503@sss.pgh.pa.us
Backpatch-through: 14
Branch
------
REL_16_STABLE
Details
-------
https://git.postgresql.org/pg/commitdiff/44e8c60be66c7c174431c4cd7948c1ff015fe516
Modified Files
--------------
src/backend/commands/async.c | 123 ++++++++++++++++++++++---------------------
1 file changed, 62 insertions(+), 61 deletions(-)
^ permalink raw reply [nested|flat] 7+ messages in thread
* pgsql: Fix remaining race condition with CLOG truncation and LISTEN/NOT
@ 2025-11-12 19:16 Heikki Linnakangas <heikki.linnakangas@iki.fi>
0 siblings, 0 replies; 7+ messages in thread
From: Heikki Linnakangas @ 2025-11-12 19:16 UTC (permalink / raw)
To: pgsql-committers@lists.postgresql.org
Fix remaining race condition with CLOG truncation and LISTEN/NOTIFY
Previous commit fixed a bug where VACUUM would truncate the CLOG
that's still needed to check the commit status of XIDs in the async
notify queue, but as mentioned in the commit message, it wasn't a full
fix. If a backend is executing asyncQueueReadAllNotifications() and
has just made a local copy of an async SLRU page which contains old
XIDs, vacuum can concurrently truncate the CLOG covering those XIDs,
and the backend still gets an error when it calls
TransactionIdDidCommit() on those XIDs in the local copy. This commit
fixes that race condition.
To fix, hold the SLRU bank lock across the TransactionIdDidCommit()
calls in NOTIFY processing.
Per Tom Lane's idea. Backpatch to all supported versions.
Reviewed-by: Joel Jacobson <joel@compiler.org>
Reviewed-by: Arseniy Mukhin <arseniy.mukhin.dev@gmail.com>
Discussion: https://www.postgresql.org/message-id/2759499.1761756503@sss.pgh.pa.us
Backpatch-through: 14
Branch
------
REL_17_STABLE
Details
-------
https://git.postgresql.org/pg/commitdiff/c2682810ab7d7127b99b4ce0db73d5db28a67c3f
Modified Files
--------------
src/backend/commands/async.c | 123 ++++++++++++++++++++++---------------------
1 file changed, 62 insertions(+), 61 deletions(-)
^ permalink raw reply [nested|flat] 7+ messages in thread
* pgsql: Fix remaining race condition with CLOG truncation and LISTEN/NOT
@ 2025-11-12 19:16 Heikki Linnakangas <heikki.linnakangas@iki.fi>
0 siblings, 0 replies; 7+ messages in thread
From: Heikki Linnakangas @ 2025-11-12 19:16 UTC (permalink / raw)
To: pgsql-committers@lists.postgresql.org
Fix remaining race condition with CLOG truncation and LISTEN/NOTIFY
Previous commit fixed a bug where VACUUM would truncate the CLOG
that's still needed to check the commit status of XIDs in the async
notify queue, but as mentioned in the commit message, it wasn't a full
fix. If a backend is executing asyncQueueReadAllNotifications() and
has just made a local copy of an async SLRU page which contains old
XIDs, vacuum can concurrently truncate the CLOG covering those XIDs,
and the backend still gets an error when it calls
TransactionIdDidCommit() on those XIDs in the local copy. This commit
fixes that race condition.
To fix, hold the SLRU bank lock across the TransactionIdDidCommit()
calls in NOTIFY processing.
Per Tom Lane's idea. Backpatch to all supported versions.
Reviewed-by: Joel Jacobson <joel@compiler.org>
Reviewed-by: Arseniy Mukhin <arseniy.mukhin.dev@gmail.com>
Discussion: https://www.postgresql.org/message-id/2759499.1761756503@sss.pgh.pa.us
Backpatch-through: 14
Branch
------
master
Details
-------
https://git.postgresql.org/pg/commitdiff/797e9ea6e54b06c3e6c79b468dab89fdbf6be179
Modified Files
--------------
src/backend/commands/async.c | 123 ++++++++++++++++++++++---------------------
1 file changed, 62 insertions(+), 61 deletions(-)
^ permalink raw reply [nested|flat] 7+ messages in thread
* pgsql: Fix remaining race condition with CLOG truncation and LISTEN/NOT
@ 2025-11-12 19:16 Heikki Linnakangas <heikki.linnakangas@iki.fi>
0 siblings, 0 replies; 7+ messages in thread
From: Heikki Linnakangas @ 2025-11-12 19:16 UTC (permalink / raw)
To: pgsql-committers@lists.postgresql.org
Fix remaining race condition with CLOG truncation and LISTEN/NOTIFY
Previous commit fixed a bug where VACUUM would truncate the CLOG
that's still needed to check the commit status of XIDs in the async
notify queue, but as mentioned in the commit message, it wasn't a full
fix. If a backend is executing asyncQueueReadAllNotifications() and
has just made a local copy of an async SLRU page which contains old
XIDs, vacuum can concurrently truncate the CLOG covering those XIDs,
and the backend still gets an error when it calls
TransactionIdDidCommit() on those XIDs in the local copy. This commit
fixes that race condition.
To fix, hold the SLRU bank lock across the TransactionIdDidCommit()
calls in NOTIFY processing.
Per Tom Lane's idea. Backpatch to all supported versions.
Reviewed-by: Joel Jacobson <joel@compiler.org>
Reviewed-by: Arseniy Mukhin <arseniy.mukhin.dev@gmail.com>
Discussion: https://www.postgresql.org/message-id/2759499.1761756503@sss.pgh.pa.us
Backpatch-through: 14
Branch
------
REL_15_STABLE
Details
-------
https://git.postgresql.org/pg/commitdiff/0c862646cf2aeba130222ec587702c331fbf3783
Modified Files
--------------
src/backend/commands/async.c | 123 ++++++++++++++++++++++---------------------
1 file changed, 62 insertions(+), 61 deletions(-)
^ permalink raw reply [nested|flat] 7+ messages in thread
* Re: pgsql: Fix remaining race condition with CLOG truncation and LISTEN/NOT
@ 2025-12-17 23:46 Michael Paquier <michael@paquier.xyz>
parent: Heikki Linnakangas <heikki.linnakangas@iki.fi>
0 siblings, 0 replies; 7+ messages in thread
From: Michael Paquier @ 2025-12-17 23:46 UTC (permalink / raw)
To: Heikki Linnakangas <heikki.linnakangas@iki.fi>; +Cc: pgsql-committers@lists.postgresql.org
Hi Heikki,
On Wed, Nov 12, 2025 at 07:16:38PM +0000, Heikki Linnakangas wrote:
> Fix remaining race condition with CLOG truncation and LISTEN/NOTIFY
>
> Previous commit fixed a bug where VACUUM would truncate the CLOG
> that's still needed to check the commit status of XIDs in the async
> notify queue, but as mentioned in the commit message, it wasn't a full
> fix. If a backend is executing asyncQueueReadAllNotifications() and
> has just made a local copy of an async SLRU page which contains old
> XIDs, vacuum can concurrently truncate the CLOG covering those XIDs,
> and the backend still gets an error when it calls
> TransactionIdDidCommit() on those XIDs in the local copy. This commit
> fixes that race condition.
>
> To fix, hold the SLRU bank lock across the TransactionIdDidCommit()
> calls in NOTIFY processing.
While reading through this set of changes, the addition of this commit
across the v14~v16 range has made me smile:
+ * Now that we have let go of the SLRU bank lock, send the notifications
+ * to our backend
SLRU bank locks have been introduced in v17 by Alvaro in 53c2a97a9266.
Just noticed while going through.
--
Michael
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2025-11-12 19:16 pgsql: Fix remaining race condition with CLOG truncation and LISTEN/NOT Heikki Linnakangas <heikki.linnakangas@iki.fi>
2025-11-12 19:16 pgsql: Fix remaining race condition with CLOG truncation and LISTEN/NOT Heikki Linnakangas <heikki.linnakangas@iki.fi>
2025-11-12 19:16 pgsql: Fix remaining race condition with CLOG truncation and LISTEN/NOT Heikki Linnakangas <heikki.linnakangas@iki.fi>
2025-11-12 19:16 pgsql: Fix remaining race condition with CLOG truncation and LISTEN/NOT Heikki Linnakangas <heikki.linnakangas@iki.fi>
2025-12-17 23:46 ` Michael Paquier <michael@paquier.xyz>
2025-11-12 19:16 pgsql: Fix remaining race condition with CLOG truncation and LISTEN/NOT Heikki Linnakangas <heikki.linnakangas@iki.fi>
2025-11-12 19:16 pgsql: Fix remaining race condition with CLOG truncation and LISTEN/NOT Heikki Linnakangas <heikki.linnakangas@iki.fi>
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