Horton

Re: Synchronizing slots from primary to standby

shveta malik <shveta.malik@gmail.com>

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From: shveta malik <shveta.malik@gmail.com>
To: Amit Kapila <amit.kapila16@gmail.com>
Cc: Masahiko Sawada <sawada.mshk@gmail.com>, "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.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>, Bertrand Drouvot <bertranddrouvot.pg@gmail.com>, shveta malik <shveta.malik@gmail.com>
Date: 2024-02-21T06:43:43Z
Lists: pgsql-hackers

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On Tue, Feb 20, 2024 at 6:56 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
>
> Miscellaneous comments:

Thanks for the comments.

> ========================
> 1.
> +void
> +ShutDownSlotSync(void)
> +{
> + SpinLockAcquire(&SlotSyncCtx->mutex);
> +
> + SlotSyncCtx->stopSignaled = true;
>
> This flag is never reset back. I think we should reset this once the
> promotion is complete. Though offhand, I don't see any problem with
> this but it doesn't look clean and can be a source of bugs in the
> future.

Did reset of flag in MaybeStartSlotSyncWorker() when we attempt to
start the worker after promotion completion and find that stopSignaled
is true while pmState is PM_RUN. From that point onwards, we can rely
on pmState to prevent the launch of the slot sync worker and thus can
reset stopSignaled.

> 2.
> +char *
> +CheckDbnameInConninfo(void)
>  {
>   char    *dbname;
>
> Let's name this function as CheckAndGetDbnameFromConninfo().

Modified.

> Apart from the above, I have made cosmetic changes in the attached.

Included these changes. Thanks.

Here are the v93 patches. It also addresses Swada-san's comment of
converting LOG to ERROR on receiving wal_level < logical.

I have also incorporated one more change wherein we check that
'Shutdown <= SmartShutdown' before launching the slot sync worker.
Since we do not need slot sync process to help in the rest of the
shutdown process, so better not to start it when shutdown (immediate
or fast) is going on. I have done this based on the details in [1]. It
is similar to WalReceiver behaviour.  Thoughts?

[1]: https://www.postgresql.org/message-id/flat/CAJpy0uCeQm2aFJLkx-D0BeAEvSdViTZf4wD7zT9coDHfLv1NaA%40mail.gmail.com

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).