Horton

Re: Synchronizing slots from primary to standby

Bertrand Drouvot <bertranddrouvot.pg@gmail.com>

View thread View on postgr.es
From: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
To: Amit Kapila <amit.kapila16@gmail.com>
Cc: shveta malik <shveta.malik@gmail.com>, Masahiko Sawada <sawada.mshk@gmail.com>, "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.com>, Peter Smith <smithpb2250@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: 2024-02-02T10:15:13Z
Lists: pgsql-hackers 
Hi,

On Fri, Feb 02, 2024 at 12:25:30PM +0530, Amit Kapila wrote:
> 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.

Big +1 for having this kind of function in user's hands (as the standby's slots
may be lagging behind during a switchover for example). As far the name, I think
it would make sense to add "replication" or "repl" something like
pg_sync_replication_slots()? (that would be aligned with
 pg_create_logical_replication_slot() and friends).

> 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?

I think that makes sense, specially if we're also creating a user callable
function to sync the slot(s) at wish.

Regards,

-- 
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com

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).