Re: [HACKERS] make async slave to wait for lsn to be replayed

Hi Alexander,

16.09.2024 21:55, Alexander Korotkov wrote:
> Please find two patches attached.  The first one does minor cleanup
> including misuse of words you've pointed.  The second one adds missing
> wait_for_catchup().  That should fix the test failure you've spotted.
> Please, check if it fixes an issue for you.

Thank you for looking at that!

Unfortunately, the issue is still here — the test failed for me 6 out of
10 runs, as below:
[05:14:02.807](0.135s) ok 8 - got error after standby promote
error running SQL: 'psql:<stdin>:1: ERROR:  recovery is not in progress
HINT:  Waiting for LSN can only be executed during recovery.'
while running 'psql -XAtq -d port=12734 host=/tmp/04hQ75NuXf dbname='postgres' -f - -v ON_ERROR_STOP=1' with sql 'CALL

pg_wal_replay_wait('0/300F248');' at .../src/test/recovery/../../../src/test/perl/PostgreSQL/Test/Cluster.pm line
2140.

043_wal_replay_wait_standby.log:
2024-09-17 05:14:02.714 UTC [1817258] 043_wal_replay_wait.pl ERROR: recovery is not in progress
2024-09-17 05:14:02.714 UTC [1817258] 043_wal_replay_wait.pl DETAIL:  Recovery ended before replaying target LSN 
2/570CD648; last replay LSN 0/300F210.
2024-09-17 05:14:02.714 UTC [1817258] 043_wal_replay_wait.pl STATEMENT:  CALL pg_wal_replay_wait('2/570CD648');
2024-09-17 05:14:02.714 UTC [1817155] LOG:  checkpoint starting: force
2024-09-17 05:14:02.714 UTC [1817154] LOG:  database system is ready to accept connections
2024-09-17 05:14:02.811 UTC [1817270] 043_wal_replay_wait.pl LOG: statement: CALL pg_wal_replay_wait('0/300F248');
2024-09-17 05:14:02.811 UTC [1817270] 043_wal_replay_wait.pl ERROR: recovery is not in progress

pg_waldump -p .../t_043_wal_replay_wait_primary_data/pgdata/pg_wal/ 000000010000000000000003
rmgr: Transaction len (rec/tot):     34/    34, tx:        748, lsn: 0/0300F1E8, prev 0/0300F1A8, desc: COMMIT 
2024-09-17 05:14:01.654874 UTC
rmgr: Standby     len (rec/tot):     50/    50, tx:          0, lsn: 0/0300F210, prev 0/0300F1E8, desc: RUNNING_XACTS 
nextXid 749 latestCompletedXid 748 oldestRunningXid 749

I wonder, can you reproduce this with that bgwriter's modification?

I've also found two more "achievements" coined by 3c5db1d6b:
doc/src/sgml/func.sgml:   It may also happen that target <acronym>lsn</acronym> is not achieved
src/backend/access/transam/xlog.c-       * recovery was ended before achieving the target LSN.

Best regards,
Alexander