pg.ddx.io pgsql-committers@postgresql.org mailing list archivehelp / color / mirror / Atom feed
pgsql: Implement WAIT FOR command 2+ messages / 2 participants [nested] [flat]
Commits from this thread: 2026-01-29 20a8f783e1 Wake LSN waiters before recovery target stop
* pgsql: Implement WAIT FOR command @ 2025-11-05 09:44 Alexander Korotkov <akorotkov@postgresql.org> 0 siblings, 1 reply; 2+ messages in thread From: Alexander Korotkov @ 2025-11-05 09:44 UTC (permalink / raw) To: pgsql-committers@lists.postgresql.org Implement WAIT FOR command WAIT FOR is to be used on standby and specifies waiting for the specific WAL location to be replayed. This option is useful when the user makes some data changes on primary and needs a guarantee to see these changes are on standby. WAIT FOR needs to wait without any snapshot held. Otherwise, the snapshot could prevent the replay of WAL records, implying a kind of self-deadlock. This is why separate utility command seems appears to be the most robust way to implement this functionality. It's not possible to implement this as a function. Previous experience shows that stored procedures also have limitation in this aspect. Discussion: https://www.postgresql.org/message-id/flat/CAPpHfdsjtZLVzxjGT8rJHCYbM0D5dwkO+BBjcirozJ6nYbOW8Q@mail.... Discussion: https://www.postgresql.org/message-id/flat/CABPTF7UNft368x-RgOXkfj475OwEbp%2BVVO-wEXz7StgjD_%3D6sw%4... Author: Kartyshov Ivan <i.kartyshov@postgrespro.ru> Author: Alexander Korotkov <aekorotkov@gmail.com> Author: Xuneng Zhou <xunengzhou@gmail.com> Reviewed-by: Michael Paquier <michael@paquier.xyz> Reviewed-by: Peter Eisentraut <peter.eisentraut@enterprisedb.com> Reviewed-by: Dilip Kumar <dilipbalaut@gmail.com> Reviewed-by: Amit Kapila <amit.kapila16@gmail.com> Reviewed-by: Alexander Lakhin <exclusion@gmail.com> Reviewed-by: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com> Reviewed-by: Euler Taveira <euler@eulerto.com> Reviewed-by: Heikki Linnakangas <hlinnaka@iki.fi> Reviewed-by: Kyotaro Horiguchi <horikyota.ntt@gmail.com> Reviewed-by: jian he <jian.universality@gmail.com> Reviewed-by: Álvaro Herrera <alvherre@kurilemu.de> Reviewed-by: Xuneng Zhou <xunengzhou@gmail.com> Branch ------ master Details ------- https://git.postgresql.org/pg/commitdiff/447aae13b0305780e87cac7b0dd669db6fab3d9d Modified Files -------------- doc/src/sgml/high-availability.sgml | 54 ++++++ doc/src/sgml/ref/allfiles.sgml | 1 + doc/src/sgml/ref/wait_for.sgml | 234 +++++++++++++++++++++++ doc/src/sgml/reference.sgml | 1 + src/backend/access/transam/xact.c | 6 + src/backend/access/transam/xlog.c | 7 + src/backend/access/transam/xlogrecovery.c | 11 ++ src/backend/commands/Makefile | 3 +- src/backend/commands/meson.build | 1 + src/backend/commands/wait.c | 212 +++++++++++++++++++++ src/backend/parser/gram.y | 33 +++- src/backend/storage/lmgr/proc.c | 6 + src/backend/tcop/pquery.c | 12 +- src/backend/tcop/utility.c | 22 +++ src/include/commands/wait.h | 22 +++ src/include/nodes/parsenodes.h | 8 + src/include/parser/kwlist.h | 2 + src/include/tcop/cmdtaglist.h | 1 + src/test/recovery/meson.build | 3 +- src/test/recovery/t/049_wait_for_lsn.pl | 302 ++++++++++++++++++++++++++++++ src/tools/pgindent/typedefs.list | 1 + 21 files changed, 931 insertions(+), 11 deletions(-) ^ permalink raw reply [nested|flat] 2+ messages in thread
* Re: pgsql: Implement WAIT FOR command @ 2026-01-26 23:33 Heikki Linnakangas <hlinnaka@iki.fi> parent: Alexander Korotkov <akorotkov@postgresql.org> 0 siblings, 0 replies; 2+ messages in thread From: Heikki Linnakangas @ 2026-01-26 23:33 UTC (permalink / raw) To: Alexander Korotkov <akorotkov@postgresql.org>; +Cc: pgsql-hackers@postgresql.org <pgsql-hackers@postgresql.org> On 05/11/2025 11:44, Alexander Korotkov wrote: > Implement WAIT FOR command Happened to just spot this: > @@ -1831,20 +1832,30 @@ PerformWalRecovery(void) > */ > ApplyWalRecord(xlogreader, record, &replayTLI); > > /* Exit loop if we reached inclusive recovery target */ > if (recoveryStopsAfter(xlogreader)) > { > reachedRecoveryTarget = true; > break; > } > > + /* > + * If we replayed an LSN that someone was waiting for then walk > + * over the shared memory array and set latches to notify the > + * waiters. > + */ > + if (waitLSNState && > + (XLogRecoveryCtl->lastReplayedEndRecPtr >= > + pg_atomic_read_u64(&waitLSNState->minWaitedLSN[WAIT_LSN_TYPE_REPLAY]))) > + WaitLSNWakeup(WAIT_LSN_TYPE_REPLAY, XLogRecoveryCtl->lastReplayedEndRecPtr); > + > /* Else, try to fetch the next WAL record */ > record = ReadRecord(xlogprefetcher, LOG, false, replayTLI); > } while (record != NULL); > > /* > * end of main redo apply loop > */ > > if (reachedRecoveryTarget) > { I think that WaitLSNWakeup() call is a little misplaced. It's after the recoveryStopsAfter() call, so if recovery is paused right after the record, the waiters won't be woken up until recovery is continued. And I suppose if recovery is stopped and the server is promoted, the waiters will never be woken up, although I didn't verify that. To fix, that should be moved to between the ApplyWalRecord() and recoveryStopsHere() calls. - Heikki ^ permalink raw reply [nested|flat] 2+ messages in thread
end of thread, other threads:[~2026-01-26 23:33 UTC | newest] Thread overview: 2+ messages (download: mbox mbox.gz follow: Atom feed) -- links below jump to the message on this page -- 2025-11-05 09:44 pgsql: Implement WAIT FOR command Alexander Korotkov <akorotkov@postgresql.org> 2026-01-26 23:33 ` Heikki Linnakangas <hlinnaka@iki.fi>
This inbox is served by DDX for PostgreSQL; see mirroring instructions for how to clone and mirror all data and code used for this inbox