Horton

Re: Synchronizing slots from primary to standby

Bertrand Drouvot <bertranddrouvot.pg@gmail.com>

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From: "Drouvot, Bertrand" <bertranddrouvot.pg@gmail.com>
To: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>, shveta malik <shveta.malik@gmail.com>
Cc: Amit Kapila <amit.kapila16@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>
Date: 2023-08-04T07:40:22Z
Lists: pgsql-hackers 
Hi,

On 7/24/23 4:32 AM, Bharath Rupireddy wrote:
> On Fri, Jul 21, 2023 at 5:16 PM shveta malik <shveta.malik@gmail.com> wrote:

> Here are my thoughts about this feature:

Thanks for looking at it!


> 
> Important considerations:
> 
> 1. Does this design guarantee the row versions required by subscribers
> aren't removed on candidate standbys as raised here -
> https://www.postgresql.org/message-id/20220218222319.yozkbhren7vkjbi5%40alap3.anarazel.de?
> 
> It seems safe with logical decoding on standbys feature. Also, a
> test-case from upthread is already in patch sets (in v9 too)
> https://www.postgresql.org/message-id/CAAaqYe9FdKODa1a9n%3Dqj%2Bw3NiB9gkwvhRHhcJNginuYYRCnLrg%40mail.gmail.com.
> However, we need to verify the use cases extensively.

Agree. We also discussed up-thread that we'd have to drop any "sync" slots if they
are invalidated. And they should be re-created based on the synchronize_slot_names.

> Please feel free to add the list if I'm missing anything.
> 

We'd also have to ensure that "sync" slots can't be consumed on the standby (this has been
discussed up-thread).

Regards,

-- 
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.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).