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Re: Implement waiting for wal lsn replay: reloaded

Thomas Munro <thomas.munro@gmail.com>

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From: Thomas Munro <thomas.munro@gmail.com>
To: Xuneng Zhou <xunengzhou@gmail.com>
Cc: Alexander Korotkov <aekorotkov@gmail.com>, Álvaro Herrera <alvherre@kurilemu.de>, Chao Li <li.evan.chao@gmail.com>, pgsql-hackers <pgsql-hackers@lists.postgresql.org>, Andres Freund <andres@anarazel.de>, Michael Paquier <michael@paquier.xyz>, jian he <jian.universality@gmail.com>, Tomas Vondra <tomas@vondra.me>, Yura Sokolov <y.sokolov@postgrespro.ru>
Date: 2026-01-06T05:42:59Z
Lists: pgsql-hackers 
Could this be causing the recent flapping failures on CI/macOS in
recovery/031_recovery_conflict?  I didn't have time to dig personally
but f30848cb looks relevant:

Waiting for replication conn standby's replay_lsn to pass 0/03467F58 on primary
error running SQL: 'psql:<stdin>:1: ERROR:  canceling statement due to
conflict with recovery
DETAIL:  User was or might have been using tablespace that must be dropped.'
while running 'psql --no-psqlrc --no-align --tuples-only --quiet
--dbname port=25195
host=/var/folders/g9/7rkt8rt1241bwwhd3_s8ndp40000gn/T/LqcCJnsueI
dbname='postgres' --file - --variable ON_ERROR_STOP=1' with sql 'WAIT
FOR LSN '0/03467F58' WITH (MODE 'standby_replay', timeout '180s',
no_throw);' at /Users/admin/pgsql/src/test/perl/PostgreSQL/Test/Cluster.pm
line 2300.

https://cirrus-ci.com/task/5771274900733952

The master branch in time-descending order, macOS tasks only:

     task_id      | substring |  status
------------------+-----------+-----------
 6460882231754752 | c970bdc0  | FAILED
 5771274900733952 | 6ca8506e  | FAILED
 6217757068361728 | 63ed3bc7  | FAILED
 5980650261446656 | ae283736  | FAILED
 6585898394976256 | 5f13999a  | COMPLETED
 4527474786172928 | 7f9acc9b  | COMPLETED
 4826100842364928 | e8d4e94a  | COMPLETED
 4540563027918848 | b9ee5f2d  | FAILED
 6358528648019968 | c5af141c  | FAILED
 5998005284765696 | e212a0f8  | COMPLETED
 6488580526178304 | b85d5dc0  | FAILED
 5034091344560128 | 7dc95cc3  | ABORTED
 5688692477526016 | bb048e31  | COMPLETED
 5481187977723904 | d351063e  | COMPLETED
 5101831568752640 | f30848cb  | COMPLETED <-- the change
 6395317408497664 | 3f33b63d  | COMPLETED
 6741325208354816 | 877ae5db  | COMPLETED
 4594007789010944 | de746e0d  | COMPLETED
 6497208998035456 | 461b8cc9  | COMPLETED

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Clean up 019_replslot_limit.pl comments

  2. Stabilize 019_replslot_limit.pl: wait on slot restart_lsn

  3. Fix memory ordering in WAIT FOR LSN wakeup mechanism

  4. Improve WAIT FOR LSN test coverage

  5. Remove redundant WAIT FOR LSN caller-side pre-checks

  6. Use barrier semantics when reading/writing writtenUpto

  7. Use replay position as floor for WAIT FOR LSN standby_(write|flush)

  8. Wake standby_write/standby_flush waiters from the WAL replay loop

  9. Minimal fix for WAIT FOR ... MODE 'standby_flush'

  10. Avoid syscache lookup while building a WAIT FOR tuple descriptor

  11. Document that WAIT FOR may be interrupted by recovery conflicts

  12. Use WAIT FOR LSN in PostgreSQL::Test::Cluster::wait_for_catchup()

  13. Wake LSN waiters before recovery target stop

  14. Remove redundant pg_unreachable() after elog(ERROR) from ExecWaitStmt()

  15. Revert "Use WAIT FOR LSN in PostgreSQL::Test::Cluster::wait_for_catchup()"

  16. Fix variable usage in wakeupWaiters()

  17. Add tab completion for the WAIT FOR LSN MODE option

  18. Add the MODE option to the WAIT FOR LSN command

  19. Extend xlogwait infrastructure with write and flush wait types

  20. Unify error messages

  21. Optimize shared memory usage for WaitLSNProcInfo

  22. Fix WaitLSNWakeup() fast-path check for InvalidXLogRecPtr

  23. Fix incorrect function name in comments

  24. Add infrastructure for efficient LSN waiting

  25. Add pairingheap_initialize() for shared memory usage

  26. Implement WAIT FOR command