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: Amit Kapila <amit.kapila16@gmail.com>
Cc: "shveta.malik@gmail.com" <shveta.malik@gmail.com>, Peter Smith <smithpb2250@gmail.com>, Bertrand Drouvot <bertranddrouvot.pg@gmail.com>, Ajin Cherian <itsajin@gmail.com>, Masahiko Sawada <sawada.mshk@gmail.com>, Dilip Kumar <dilipbalaut@gmail.com>, Euler Taveira <euler@eulerto.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: 2024-02-05T03:49:23Z
Lists: pgsql-hackers

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On Thursday, February 1, 2024 12:20 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
> 
> On Thu, Feb 1, 2024 at 8:15 AM Euler Taveira <euler@eulerto.com> wrote:
> >
> > On Mon, Jan 29, 2024, at 10:17 AM, Zhijie Hou (Fujitsu) wrote:
> >
> > Attach the V72-0001 which addressed above comments, other patches will
> be
> > rebased and posted after pushing first patch. Thanks Shveta for helping
> address
> > the comments.
> >
> >
> > While working on another patch I noticed a new NOTICE message:
> >
> > NOTICE:  changed the failover state of replication slot "foo" on publisher to
> false
> >
> > I wasn't paying much attention to this thread then I start reading the 2
> > patches that was recently committed. The message above surprises me
> because
> > pg_createsubscriber starts to emit this message. The reason is that it doesn't
> > create the replication slot during the CREATE SUBSCRIPTION. Instead, it
> creates
> > the replication slot with failover = false and no such option is informed
> > during CREATE SUBSCRIPTION which means it uses the default value (failover
> =
> > false). I expect that I don't see any message because it is *not* changing the
> > behavior. I was wrong. It doesn't check the failover state on publisher, it
> > just executes walrcv_alter_slot() and emits a message.
> >
> > IMO if we are changing an outstanding property on node A from node B,
> node B
> > already knows (or might know) about that behavior change (because it is
> sending
> > the command), however, node A doesn't (unless log_replication_commands
> = on --
> > it is not the default).
> >
> > Do we really need this message as NOTICE?
> >
> 
> The reason for adding this NOTICE was to keep it similar to other
> Notice messages in these commands like create/drop slot. However, here
> the difference is we may not have altered the slot as the property is
> already the same as we want to set on the publisher. So, I am not sure
> whether we should follow the existing behavior or just get rid of it.
> And then do we remove similar NOTICE in AlterSubscription() as well?
> Normally, I think NOTICE intends to let users know if we did anything
> with slots while executing subscription commands. Does anyone else
> have an opinion on this point?
> 
> A related point, I think we can avoid setting the 'failover' property
> in ReplicationSlotAlter() if it is not changed, the advantage is we
> will avoid saving slots. OTOH, this won't be a frequent operation so
> we can leave it as it is as well.

Here is a patch to remove the NOTICE and improve the ReplicationSlotAlter.
The patch also includes few cleanups based on Peter's feedback.

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).