Horton

Re: Synchronizing slots from primary to standby

Amit Kapila <amit.kapila16@gmail.com>

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From: Amit Kapila <amit.kapila16@gmail.com>
To: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
Cc: "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.com>, shveta malik <shveta.malik@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>, Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.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: 2024-04-02T08:49:30Z
Lists: pgsql-hackers 
On Tue, Apr 2, 2024 at 1:54 PM Bertrand Drouvot
<bertranddrouvot.pg@gmail.com> wrote:
>
> On Tue, Apr 02, 2024 at 07:20:46AM +0000, Zhijie Hou (Fujitsu) wrote:
> > I added one test in 040_standby_failover_slots_sync.pl in 0002 patch, which can
> > reproduce the data loss issue consistently on my machine.
>
> Thanks!
>
> > It may not reproduce
> > in some rare cases if concurrent xl_running_xacts are written by bgwriter, but
> > I think it's still valuable if it can verify the fix in most cases.
>
> What about adding a "wait" injection point in LogStandbySnapshot() to prevent
> checkpointer/bgwriter to log a standby snapshot? Something among those lines:
>
>        if (AmCheckpointerProcess() || AmBackgroundWriterProcess())
>                INJECTION_POINT("bgw-log-standby-snapshot");
>
> And make use of it in the test, something like:
>
>        $node_primary->safe_psql('postgres',
>                "SELECT injection_points_attach('bgw-log-standby-snapshot', 'wait');");
>

Sometimes we want the checkpoint to log the standby snapshot as we
need it at a predictable time, maybe one can use
pg_log_standby_snapshot() instead of that. Can we add an injection
point as a separate patch/commit after a bit more discussion? I want
to discuss this in a separate thread so that later we should not get
an objection to adding an injection_point at this location. One other
idea to make such tests predictable is to add a developer-specific GUC
say debug_bg_log_standby_snapshot or something like that but injection
point sounds like a better idea.

-- 
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).