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: Peter Eisentraut <peter.eisentraut@enterprisedb.com>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2021-11-24T06:11:51Z
Lists: pgsql-hackers 
On Sun, Oct 31, 2021 at 7:08 PM Peter Eisentraut
<peter.eisentraut@enterprisedb.com> wrote:
>
> I want to reactivate $subject.  I took Petr Jelinek's patch from [0],
> rebased it, added a bit of testing.  It basically works, but as
> mentioned in [0], there are various issues to work out.

Thank you for working on this feature!

>
> The idea is that the standby runs a background worker to periodically
> fetch replication slot information from the primary.  On failover, a
> logical subscriber would then ideally find up-to-date replication slots
> on the new publisher and can just continue normally.
>
>   I have also found that this breaks some seemingly unrelated tests in
> the recovery test suite.  I have disabled these here.  I'm not sure if
> the patch actually breaks anything or if these are just differences in
> timing or implementation dependencies.

I haven’t looked at the patch deeply but regarding 007_sync_rep.pl,
the tests seem to fail since the tests rely on the order of the wal
sender array on the shared memory. Since a background worker for
synchronizing replication slots periodically connects to the walsender
on the primary and disconnects, it breaks the assumption of the order.
Regarding 010_logical_decoding_timelines.pl, I guess that the patch
breaks the test because the background worker for synchronizing slots
on the replica periodically advances the replica's slot. I think we
need to have a way to disable the slot synchronization or to specify
the slot name to sync with the primary. I'm not sure we already
discussed this topic but I think we need it at least for testing
purposes.

Regards,

--
Masahiko Sawada
EDB:  https://www.enterprisedb.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).