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: Peter Smith <smithpb2250@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: 2024-03-04T03:38:20Z
Lists: pgsql-hackers 
On Mon, Mar 4, 2024 at 6:57 AM Peter Smith <smithpb2250@gmail.com> wrote:
>
> On Sun, Mar 3, 2024 at 2:56 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
> >
> > On Sun, Mar 3, 2024 at 5:17 AM Peter Smith <smithpb2250@gmail.com> wrote:
> > >
> ...
> > > 9. NeedToWaitForWal
> > >
> > > + /*
> > > + * Check if the standby slots have caught up to the flushed position. It
> > > + * is good to wait up to flushed position and then let it send the changes
> > > + * to logical subscribers one by one which are already covered in flushed
> > > + * position without needing to wait on every change for standby
> > > + * confirmation. Note that after receiving the shutdown signal, an ERROR
> > > + * is reported if any slots are dropped, invalidated, or inactive. This
> > > + * measure is taken to prevent the walsender from waiting indefinitely.
> > > + */
> > > + if (NeedToWaitForStandby(target_lsn, flushed_lsn, wait_event))
> > > + return true;
> > >
> > > I felt it was confusing things for this function to also call to the
> > > other one -- it seems an overlapping/muddling of the purpose of these.
> > > I think it will be easier to understand if the calling code just calls
> > > to one or both of these functions as required.
> > >
> >
> > I felt otherwise because the caller has to call these functions at
> > more than one place which makes the caller's code difficult to follow.
> > It is better to encapsulate the computation of wait_event.
> >
>
> You may have misinterpreted my review comment because I didn't say
> anything about changing the encapsulation of the computation of the
> wait_event.
>

No, I have understood it in the same way as you have outlined in this
email and liked the way the current patch has it.

-- 
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).