Horton

Re: Synchronizing slots from primary to standby

Bertrand Drouvot <bertranddrouvot.pg@gmail.com>

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From: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
To: "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.com>
Cc: shveta malik <shveta.malik@gmail.com>, Amit Kapila <amit.kapila16@gmail.com>, Masahiko Sawada <sawada.mshk@gmail.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: 2024-02-23T11:15:51Z
Lists: pgsql-hackers 
Hi,

On Fri, Feb 23, 2024 at 09:46:00AM +0000, Zhijie Hou (Fujitsu) wrote:
> On Friday, February 23, 2024 1:22 PM shveta malik <shveta.malik@gmail.com> wrote:
> 
> > 
> > Thanks for the patches. Had a quick look at v95_2, here are some
> > trivial comments:
> 
> Thanks for the comments.
> 
> > 6) streaming replication standby server slot names that logical walsender
> > processes will wait for
> > 
> > Is it better to say it like this? (I leave this to your preference)
> > 
> > streaming replication standby server slot names for which logical
> > walsender processes will wait.
> 
> I feel the current one seems better, so didn’t change. Other comments have been
> addressed. Here is the V97 patch set which addressed Shveta's comments.
> 
> 
> Besides, I'd like to clarify and discuss the behavior of standby_slot_names once.
> 
> As it stands in the patch, If the slots specified in standby_slot_names are
> dropped or invalidated, the logical walsender will issue a WARNING and continue
> to replicate the changes. Another option for this could be to have the
> walsender pause until the slot in standby_slot_names is re-created or becomes
> valid again. Does anyone else have an opinion on this matter ?

Good point, I'd vote for: the only reasons not to wait are:

- slots mentioned in standby_slot_names exist and valid and do catch up
or
- standby_slot_names is empty

The reason is that setting standby_slot_names to a non empty value means that
one wants the walsender to wait until the standby catchup. The way to remove this
intentional behavior should be by changing the standby_slot_names value (not the
existence or the state of the slot(s) it points too).

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).