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: Ajin Cherian <itsajin@gmail.com>
Cc: Amit Kapila <amit.kapila16@gmail.com>, Bertrand Drouvot <bertranddrouvot.pg@gmail.com>, Masahiko Sawada <sawada.mshk@gmail.com>, "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.com>, Dilip Kumar <dilipbalaut@gmail.com>, Peter Smith <smithpb2250@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>, shveta malik <shveta.malik@gmail.com>
Date: 2024-01-23T11:43:12Z
Lists: pgsql-hackers

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On Tue, Jan 23, 2024 at 2:38 PM Ajin Cherian <itsajin@gmail.com> wrote:
>
> I was doing some testing on this. What I noticed is that creating subscriptions with failover enabled is taking a lot longer compared with a subscription with failover disabled. The setup has primary configured with standby_slot_names and that standby is enabled with enable_synclot turned on.
>

Thanks Ajin for testing the patch. PFA v66 which fixes this issue.

The overall changes in this version are:

patch 001
1) Restricted enabling failover for user created slots on standby.
2) Fixed a wrong NOTICE during alter-sub which was always saying that
'changed the failover state to false' even if it was switched to true.

patch 002:
3) Addressed Peter's comment in [1]

patch 003:
4) Fixed the drop-db issue reported by Swada-San in [2]
5) Added other signal-handlers.
6) Fixed CFBot Windows compilation failure.

patch 004:
7) Fixed the issue reported by Ajin above in [3]. The performance
issue was due to the additional wait in WalSndWaitForWal() for
failover slots. Create Subscription calls
DecodingContextFindStartpoint() which then reads WALs to build the
initial snapshot which ends up calling WalSndWaitForWal() which waits
for standby confirmation for the case of failover slots. Addressed it
by skipping the wait during Create Sub as it is not needed there. We
now wait only if 'replication_active' is true.

Thanks Nisha for reporting the NOTICE issue (addressed in 2) and
working on issue #6.

Thanks Hou-San for working on #7.

[1]: https://www.postgresql.org/message-id/CAHut%2BPs6p6Km8_Hfy6X0KTuyqBKkhC84u23sQnnkhqkHuDL%2BDQ%40mail.gmail.com
[2]: https://www.postgresql.org/message-id/CAD21AoBgzONdt3o5mzbQ4MtqAE%3DWseiXUOq0LMqne-nWGjZBsA%40mail.gmail.com
[3]: https://www.postgresql.org/message-id/CAFPTHDbsZ%2BpxAubb9d9BwVNt5OB3_2s77bG6nHcAgUPPhEVmMQ%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).