Horton

Re: Synchronizing slots from primary to standby

Masahiko Sawada <sawada.mshk@gmail.com>

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From: Masahiko Sawada <sawada.mshk@gmail.com>
To: Amit Kapila <amit.kapila16@gmail.com>
Cc: shveta malik <shveta.malik@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>, Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
Date: 2024-02-20T13:10:44Z
Lists: pgsql-hackers 
On Tue, Feb 20, 2024 at 12:44 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
>
> On Tue, Feb 20, 2024 at 8:25 AM Masahiko Sawada <sawada.mshk@gmail.com> wrote:
> >
> > Some comments not related to the patch but to the existing code:
> >
> > ---
> > It might have already been discussed but is the
> > src/backend/replication/logical the right place for the slocsync.c? If
> > it's independent of logical decoding/replication, is under
> > src/backend/replication could be more appropriate?
> >

Thank you for the comment.

>
> This point has not been discussed, so thanks for raising it. I think
> the reasoning behind keeping it in logical is that this file contains
> a code for logical slot syncing and a worker doing that. As it is
> mostly about logical slot syncing so there is an argument to keep it
> under logical. In the future, we may need to extend this functionality
> to have a per-db slot sync worker as well in which case it will
> probably be again somewhat related to logical slots.

That's a valid argument.

> Having said that,
> there is an argument to keep it under replication as well because the
> functionality it provides is for physical standbys.

Another argument to keep it under replication is; all files under the
replication/logical directory are logical decoding and logical
replication infrastructures. IOW these are the functionality built on
top of (logical) replication slots. On the other hand, the slotsync
worker (and slotsync functionality) looks a part of slot management
functionality, which seems the same layer of slot.c.

BTW the slotsync.c of v91 patch includes "replication/logical.h" but
it isn't actually necessary and #include'ing "replication/slot.h" is
sufficient.

Regards

-- 
Masahiko Sawada
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).