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: Masahiko Sawada <sawada.mshk@gmail.com>
Cc: shveta malik <shveta.malik@gmail.com>, Ajin Cherian <itsajin@gmail.com>, "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.com>, Peter Smith <smithpb2250@gmail.com>, Bertrand Drouvot <bertranddrouvot.pg@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: 2024-02-06T11:21:02Z
Lists: pgsql-hackers 
On Tue, Feb 6, 2024 at 3:33 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
>
> On Tue, Feb 6, 2024 at 1:09 PM Masahiko Sawada <sawada.mshk@gmail.com> wrote:
> >
> > On Tue, Feb 6, 2024 at 3:19 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
> > >
> > > I think users can refer to LOGs to see if it has changed since the
> > > first time it was configured. I tried by existing parameter and see
> > > the following in LOG:
> > > LOG:  received SIGHUP, reloading configuration files
> > > 2024-02-06 11:38:59.069 IST [9240] LOG:  parameter "autovacuum" changed to "on"
> > >
> > > If the user can't confirm then it is better to follow the steps
> > > mentioned in the patch. Do you want something else to be written in
> > > docs for this? If so, what?
> >
> > IIUC even if a wrong slot name is specified to standby_slot_names or
> > even standby_slot_names is empty, the standby server might not be
> > lagging behind the subscribers depending on the timing. But when
> > checking it the next time, the standby server might lag behind the
> > subscribers. So what I wanted to know is how the user can confirm if a
> > failover-enabled subscription is ensured not to go in front of
> > failover-candidate standbys (i.e., standbys using the slots listed in
> > standby_slot_names).
> >
>
> But isn't the same explained by two steps ((a) Firstly, on the
> subscriber node check the last replayed WAL. (b) Next, on the standby
> server check that the last-received WAL location is ahead of the
> replayed WAL location on the subscriber identified above.) in the
> latest *_0004 patch.
>

Additionally, I would like to add that the users can use the queries
mentioned in the doc after the primary has failed and before promoting
the standby. If she wants to do that when both primary and standby are
available, the value of 'standby_slot_names' on primary should be
referred. Isn't those two sufficient that there won't be false
positives?

-- 
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).