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pgsql: Re-register LSN waiters after stale wakeups 2+ messages / 1 participants [nested] [flat]
* pgsql: Re-register LSN waiters after stale wakeups @ 2026-08-18 12:02 Alexander Korotkov <akorotkov@postgresql.org> 0 siblings, 0 replies; 2+ messages in thread From: Alexander Korotkov @ 2026-08-18 12:02 UTC (permalink / raw) To: pgsql-committers@lists.postgresql.org Re-register LSN waiters after stale wakeups WaitLSNWakeup() removes a waiter from the heap before setting its latch. If the position that caused the wakeup moves backwards before the waiter rechecks it, as can happen when WAL streaming restarts, the waiter may sleep again while no longer registered. Subsequent WAL progress then cannot wake it. When an unmet waiter finds that it is no longer in the heap, add it back and restart the loop. Rereading the position after registration also prevents missing an advance between the previous read and the re-add. Process interrupts before re-registering rather than after, so that a wakeup which goes stale again cannot postpone cancellation, however often it repeats. As a side effect, a pending cancel now wins over an expired timeout, which previously reported a timeout instead. Add deterministic TAP coverage that simulates a stale standby_write wakeup without advancing the actual write or replay positions. Author: Xuneng Zhou <xunengzhou@gmail.com> Reviewed-by: Alexander Korotkov <aekorotkov@gmail.com> Discussion: https://postgr.es/m/CABPTF7UtW_cAa%3DQh4RDfKiUqu3pJJE22ai9tbWJVERbeRyssLw%40mail.gmail.com Backpatch-through: 19 Branch ------ master Details ------- https://git.postgresql.org/pg/commitdiff/70b7e968d5773026ea5105ae7ff23d362bf9723d Modified Files -------------- src/backend/access/transam/xlogwait.c | 37 +++++++- src/test/modules/Makefile | 1 + src/test/modules/meson.build | 1 + src/test/modules/test_wait_lsn/Makefile | 21 +++++ src/test/modules/test_wait_lsn/meson.build | 22 +++++ .../modules/test_wait_lsn/test_wait_lsn--1.0.sql | 14 +++ src/test/modules/test_wait_lsn/test_wait_lsn.c | 99 ++++++++++++++++++++++ .../modules/test_wait_lsn/test_wait_lsn.control | 4 + src/test/recovery/Makefile | 3 +- src/test/recovery/t/049_wait_for_lsn.pl | 85 +++++++++++++++++++ 10 files changed, 284 insertions(+), 3 deletions(-) ^ permalink raw reply [nested|flat] 2+ messages in thread
* pgsql: Re-register LSN waiters after stale wakeups @ 2026-08-18 12:02 Alexander Korotkov <akorotkov@postgresql.org> 0 siblings, 0 replies; 2+ messages in thread From: Alexander Korotkov @ 2026-08-18 12:02 UTC (permalink / raw) To: pgsql-committers@lists.postgresql.org Re-register LSN waiters after stale wakeups WaitLSNWakeup() removes a waiter from the heap before setting its latch. If the position that caused the wakeup moves backwards before the waiter rechecks it, as can happen when WAL streaming restarts, the waiter may sleep again while no longer registered. Subsequent WAL progress then cannot wake it. When an unmet waiter finds that it is no longer in the heap, add it back and restart the loop. Rereading the position after registration also prevents missing an advance between the previous read and the re-add. Process interrupts before re-registering rather than after, so that a wakeup which goes stale again cannot postpone cancellation, however often it repeats. As a side effect, a pending cancel now wins over an expired timeout, which previously reported a timeout instead. Add deterministic TAP coverage that simulates a stale standby_write wakeup without advancing the actual write or replay positions. Author: Xuneng Zhou <xunengzhou@gmail.com> Reviewed-by: Alexander Korotkov <aekorotkov@gmail.com> Discussion: https://postgr.es/m/CABPTF7UtW_cAa%3DQh4RDfKiUqu3pJJE22ai9tbWJVERbeRyssLw%40mail.gmail.com Backpatch-through: 19 Branch ------ REL_19_STABLE Details ------- https://git.postgresql.org/pg/commitdiff/0ec36f4ba325062882eb7a36b8f815e85ff8c123 Modified Files -------------- src/backend/access/transam/xlogwait.c | 37 +++++++- src/test/modules/Makefile | 1 + src/test/modules/meson.build | 1 + src/test/modules/test_wait_lsn/Makefile | 21 +++++ src/test/modules/test_wait_lsn/meson.build | 22 +++++ .../modules/test_wait_lsn/test_wait_lsn--1.0.sql | 14 +++ src/test/modules/test_wait_lsn/test_wait_lsn.c | 99 ++++++++++++++++++++++ .../modules/test_wait_lsn/test_wait_lsn.control | 4 + src/test/recovery/Makefile | 3 +- src/test/recovery/t/049_wait_for_lsn.pl | 85 +++++++++++++++++++ 10 files changed, 284 insertions(+), 3 deletions(-) ^ permalink raw reply [nested|flat] 2+ messages in thread
end of thread, other threads:[~2026-08-18 12:02 UTC | newest] Thread overview: 2+ messages (download: mbox mbox.gz follow: Atom feed) -- links below jump to the message on this page -- 2026-08-18 12:02 pgsql: Re-register LSN waiters after stale wakeups Alexander Korotkov <akorotkov@postgresql.org> 2026-08-18 12:02 pgsql: Re-register LSN waiters after stale wakeups Alexander Korotkov <akorotkov@postgresql.org>
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