Horton

Re: Synchronizing slots from primary to standby

Peter Smith <smithpb2250@gmail.com>

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From: Peter Smith <smithpb2250@gmail.com>
To: Amit Kapila <amit.kapila16@gmail.com>
Cc: "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.com>, shveta malik <shveta.malik@gmail.com>, Masahiko Sawada <sawada.mshk@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>, Bertrand Drouvot <bertranddrouvot.pg@gmail.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: 2024-02-29T03:43:30Z
Lists: pgsql-hackers 
On Tue, Feb 27, 2024 at 11:35 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
>
> On Tue, Feb 27, 2024 at 12:48 PM Peter Smith <smithpb2250@gmail.com> wrote:
> >
> > Here are some review comments for v99-0001
> >
> > ==========
> > 0. GENERAL.
> >
> > +#standby_slot_names = '' # streaming replication standby server slot names that
> > + # logical walsender processes will wait for
> >
> > IMO the GUC name is too generic. There is nothing in this name to
> > suggest it has anything to do with logical slot synchronization; that
> > meaning is only found in the accompanying comment -- it would be
> > better if the GUC name itself were more self-explanatory.
> >
> > e.g. Maybe like 'wal_sender_sync_standby_slot_names' or
> > 'wal_sender_standby_slot_names', 'wal_sender_wait_for_standby_slots',
> > or ...
> >
>
> It would be wrong and or misleading to append wal_sender to this GUC
> name as this is used during SQL APIs as well.

Fair enough, but the fact that some SQL functions might wait is also
not mentioned in the config file comment, nor in the documentation for
GUC  'standby_slot_names'. Seems like a docs omission?

> Also, adding wait sounds
> more like a boolean. So, I don't see the proposed names any better
> than the current one.
>

Anyway, the point is that the current GUC name 'standby_slot_names' is
not ideal IMO because it doesn't have enough meaning by itself -- e.g.
you have to read the accompanying comment or documentation to have any
idea of its purpose.

My suggested GUC names were mostly just to get people thinking about
it. Maybe others can come up with better names.

======
Kind Regards,
Peter Smith.
Fujitsu Australia

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).