Horton

Re: Synchronizing slots from primary to standby

shveta malik <shveta.malik@gmail.com>

View thread View on postgr.es
From: shveta malik <shveta.malik@gmail.com>
To: Ajin Cherian <itsajin@gmail.com>
Cc: Amit Kapila <amit.kapila16@gmail.com>, "Drouvot, Bertrand" <bertranddrouvot.pg@gmail.com>, Peter Smith <smithpb2250@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>, shveta malik <shveta.malik@gmail.com>
Date: 2023-11-13T06:38:37Z
Lists: pgsql-hackers 
On Mon, Nov 13, 2023 at 11:02 AM Ajin Cherian <itsajin@gmail.com> wrote:
>
> On Thu, Nov 9, 2023 at 9:54 PM shveta malik <shveta.malik@gmail.com> wrote:
> >
> > PFA v32 patches which has below changes:
> Testing with this patch, I see that if the failover enabled slot is
> invalidated on the primary, then the corresponding synced slot is not
> invalidated on the standby. Instead, I see that it continuously gets
> the below error:
> " WARNING:  not synchronizing slot sub; synchronization would move it backwards"
>
> In the code, I see that:
>         if (remote_slot->restart_lsn < MyReplicationSlot->data.restart_lsn)
>         {
>             ereport(WARNING,
>                     errmsg("not synchronizing slot %s; synchronization
> would move"
>                            " it backwards", remote_slot->name));
>
>             ReplicationSlotRelease();
>             CommitTransactionCommand();
>             return;
>         }
>
> If the restart_lsn of the remote slot is behind, then the
> local_slot_update() function is never called to set the invalidation
> status on the local slot. And for invalidated slots, restart_lsn is
> always NULL.
>

Okay. Thanks for testing Ajin. I think it needs a fix wherein we set
the local-slot's invalidation status (provided it is not invalidated
already) from the remote slot before this check itself. And if the
slot is invalidated locally (either by itself) or by primary_slot
being invalidated, then we should skip the sync. I will fix this in
the next version.

thanks
Shveta

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).