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: shveta malik <shveta.malik@gmail.com>
Cc: Masahiko Sawada <sawada.mshk@gmail.com>, "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.com>, Peter Smith <smithpb2250@gmail.com>, Bertrand Drouvot <bertranddrouvot.pg@gmail.com>, Ajin Cherian <itsajin@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: 2024-02-02T06:55:30Z
Lists: pgsql-hackers 
On Thu, Feb 1, 2024 at 5:29 PM shveta malik <shveta.malik@gmail.com> wrote:
>
> On Thu, Feb 1, 2024 at 2:35 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
> >
> > Agreed, and I am fine with merging 0001, 0002, and 0004 as suggested
> > by you though I have a few minor comments on 0002 and 0004. I was
> > thinking about what will be a logical way to split the slot sync
> > worker patch (combined result of 0001, 0002, and 0004), and one idea
> > occurred to me is that we can have the first patch as
> > synchronize_solts() API and the functionality required to implement
> > that API then the second patch would be a slot sync worker which uses
> > that API to synchronize slots and does all the required validations.
> > Any thoughts?
>
> If we shift 'synchronize_slots()' to the first patch but there is no
> caller of it, we may have a compiler warning for the same. The only
> way it can be done is if we temporarily add SQL function on standby
> which uses 'synchronize_slots()'. This SQL function can then be
> removed in later patches where we actually have a caller for
> 'synchronize_slots'.
>

Can such a SQL function say pg_synchronize_slots() which can sync all
slots that have a failover flag set be useful in general apart from
just writing tests for this new API? I am thinking maybe users want
more control over when to sync the slots and write their bgworker or
simply do it just before shutdown once (sort of planned switchover) or
at some other pre-defined times. BTW, we also have
pg_log_standby_snapshot() which otherwise would be done periodically
by background processes.

>
> 1) Re-arranged the patches:
> 1.1) 'libpqrc' related changes (from v74-001 and v74-004) are
> separated out in v75-001 as those are independent changes.

Bertrand, Sawada-San, and others, do you see a problem with such a
split? Can we go ahead with v75_0001 separately after fixing the open
comments?

-- 
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).