Horton

RE: Synchronizing slots from primary to standby

Zhijie Hou (Fujitsu) <houzj.fnst@fujitsu.com>

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From: "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.com>
To: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>, Amit Kapila <amit.kapila16@gmail.com>
Cc: 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: 2024-04-02T04:24:49Z
Lists: pgsql-hackers

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On Monday, April 1, 2024 9:28 PM Bertrand Drouvot <bertranddrouvot.pg@gmail.com> wrote:
> 
> On Mon, Apr 01, 2024 at 05:04:53PM +0530, Amit Kapila wrote:
> > On Mon, Apr 1, 2024 at 2:51 PM Bertrand Drouvot
> 
> >
> > > 2 ===
> > >
> > > +       {
> > > +               if (SnapBuildSnapshotExists(remote_slot->restart_lsn))
> > > +               {
> > >
> > > That could call SnapBuildSnapshotExists() multiple times for the
> > > same "restart_lsn" (for example in case of multiple remote slots to sync).
> > >
> > > What if the sync worker records the last lsn it asks for
> > > serialization (and serialized ? Then we could check that value first
> > > before deciding to call (or not)
> > > SnapBuildSnapshotExists() on it?
> > >
> > > It's not ideal because it would record "only the last one" but that
> > > would be simple enough for now (currently there is only one sync
> > > worker so that scenario is likely to happen).
> > >
> >
> > Yeah, we could do that but I am not sure how much it can help. I guess
> > we could do some tests to see if it helps.
> 
> Yeah not sure either. I just think it can only help and shouldn't make things
> worst (but could avoid extra SnapBuildSnapshotExists() calls).

Thanks for the idea. I tried some tests based on Nisha's setup[1]. I tried to
advance the slots on the primary to the same restart_lsn before calling
sync_replication_slots(), and reduced the data generated by pgbench. The
SnapBuildSnapshotExists is still not noticeable in the profile. So, I feel we
could leave this as a further improvement once we encounter scenarios where
the duplicate SnapBuildSnapshotExists call becomes noticeable.

[1] https://www.postgresql.org/message-id/CALj2ACUeij5tFzJ1-cuoUh%2Bmhj33v%2BYgqD_gHYUpRdXSCSBbhw%40mail.gmail.com

Best Regards,
Hou zj

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).