Horton

Re: Synchronizing slots from primary to standby

Amit Kapila <amit.kapila16@gmail.com>

View thread View on postgr.es
From: Amit Kapila <amit.kapila16@gmail.com>
To: "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.com>
Cc: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>, shveta malik <shveta.malik@gmail.com>, Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>, Ajin Cherian <itsajin@gmail.com>, Peter Smith <smithpb2250@gmail.com>, Masahiko Sawada <sawada.mshk@gmail.com>, Dilip Kumar <dilipbalaut@gmail.com>, Nisha Moond <nisha.moond412@gmail.com>, "Hayato Kuroda (Fujitsu)" <kuroda.hayato@fujitsu.com>, Peter Eisentraut <peter.eisentraut@enterprisedb.com>, Bruce Momjian <bruce@momjian.us>, Ashutosh Sharma <ashu.coek88@gmail.com>, Andres Freund <andres@anarazel.de>, pgsql-hackers <pgsql-hackers@postgresql.org>, Alvaro Herrera <alvherre@alvh.no-ip.org>
Date: 2024-04-09T05:13:18Z
Lists: pgsql-hackers 
On Mon, Apr 8, 2024 at 7:01 PM Zhijie Hou (Fujitsu)
<houzj.fnst@fujitsu.com> wrote:
>
> Thanks for pushing.
>
> I checked the BF status, and noticed one BF failure, which I think is related to
> a miss in the test code.
> https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=adder&dt=2024-04-08%2012%3A04%3A27
>
> From the following log, I can see the sync failed because the standby is
> lagging behind of the failover slot.
>
> -----
> # No postmaster PID for node "cascading_standby"
> error running SQL: 'psql:<stdin>:1: ERROR:  skipping slot synchronization as the received slot sync LSN 0/4000148 for slot "snap_test_slot" is ahead of the standby position 0/4000114'
> while running 'psql -XAtq -d port=50074 host=/tmp/t4HQFlrDmI dbname='postgres' -f - -v ON_ERROR_STOP=1' with sql 'SELECT pg_sync_replication_slots();' at /home/bf/bf-build/adder/HEAD/pgsql/src/test/perl/PostgreSQL/Test/Cluster.pm line 2042.
> # Postmaster PID for node "publisher" is 3715298
> -----
>
> I think it's because we missed to call wait_for_replay_catchup before syncing
> slots.
>
> -----
> $primary->safe_psql('postgres',
>         "SELECT pg_create_logical_replication_slot('snap_test_slot', 'test_decoding', false, false, true);"
> );
> # ? missed to wait here
> $standby1->safe_psql('postgres', "SELECT pg_sync_replication_slots();");
> -----
>
> While testing, I noticed another place where we were calling
> wait_for_replay_catchup before doing pg_replication_slot_advance, which also has
> a small possibility to cause the failover slot to be ahead of the standby if
> some logs are written in between these two steps. So, I adjusted them together.
>
> Here is a small patch to improve the test.
>

LGTM. I'll push this tomorrow morning unless there are any more
comments or suggestions.

-- 
With Regards,
Amit Kapila.

Commits

  1. Doc: Add the new section "Logical Replication Failover".

  2. Fix the review comments and a bug in the slot sync code.

  3. Fix a test in failover slots regression test.

  4. Fix the intermittent buildfarm failures in 040_standby_failover_slots_sync.

  5. Split XLogCtl->LogwrtResult into separate struct members

  6. Ensure that the sync slots reach a consistent state after promotion without losing data.

  7. Introduce a new GUC 'standby_slot_names'.

  8. Fix BF failure introduced by commit b3f6b14cf4.

  9. Fixups for commit 93db6cbda0.

  10. Fix BF failure in commit 93db6cbda0.

  11. Add a new slot sync worker to synchronize logical slots.

  12. Improve ERROR/LOG messages added by commits ddd5f4f54a and 7a424ece48.

  13. Disable autovacuum on primary in 040_standby_failover_slots_sync test.

  14. Fix the incorrect format specifier used in commit 7a424ece48.

  15. Change the LOG level in 040_standby_failover_slots_sync.pl to DEBUG2.

  16. Add more LOG and DEBUG messages for slot synchronization.

  17. Another try to fix BF failure introduced in commit ddd5f4f54a.

  18. Fix BF introduced in commit ddd5f4f54a.

  19. Add a slot synchronization function.

  20. Clean-ups for 776621a5e4 and 7329240437.

  21. Enhance libpqrcv APIs to support slot synchronization.

  22. Add a failover option to subscriptions.

  23. Allow setting failover property in the replication command.

  24. Allow to enable failover property for replication slots via SQL API.

  25. Add macros for looping through a List without a ListCell.

  26. Track conflict_reason in pg_replication_slots.

  27. Allow upgrades to preserve the full subscription's state.

  28. Add support for incremental backup.

  29. Simplify some logic in CreateReplicationSlot()

  30. Fix uninitialized access to InitialRunningXacts during decoding after ERROR.

  31. Flexible options for CREATE_REPLICATION_SLOT.

  32. Empty search_path in logical replication apply worker and walsender.

  33. Fix oldest xmin and LSN computation across repslots after advancing

  34. Require C99 (and thus MSCV 2013 upwards).