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Re: Synchronizing slots from primary to standby

Bertrand Drouvot <bertranddrouvot.pg@gmail.com>

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From: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
To: "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.com>
Cc: Amit Kapila <amit.kapila16@gmail.com>, Masahiko Sawada <sawada.mshk@gmail.com>, Dilip Kumar <dilipbalaut@gmail.com>, shveta malik <shveta.malik@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>, Ajin Cherian <itsajin@gmail.com>, Alvaro Herrera <alvherre@alvh.no-ip.org>
Date: 2024-01-12T06:54:09Z
Lists: pgsql-hackers 
Hi,

On Fri, Jan 12, 2024 at 03:46:00AM +0000, Zhijie Hou (Fujitsu) wrote:
> On Thursday, January 11, 2024 11:42 PM Bertrand Drouvot <bertranddrouvot.pg@gmail.com> wrote:
> 
> Hi,
>  
> > On Thu, Jan 11, 2024 at 04:22:56PM +0530, Amit Kapila wrote:
> > IIUC, this would be a sync slot (so not usable until promotion) that could not be
> > used anyway (invalidated), so I'll vote for drop / re-create then.
> 
> Such race can happen when user drop and re-create the same failover slot on
> primary as well. For example, user dropped one failover slot and them
> immediately created a new one by copying from an old slot(using
> pg_copy_logical_replication_slot). Then the slotsync worker will find the
> restart_lsn of this slot go backwards.
> 
> The steps:
> ----
> SELECT 'init' FROM pg_create_logical_replication_slot('isolation_slot', 'pgoutput', false, false, true);
> SELECT 'init' FROM pg_create_logical_replication_slot('test', 'pgoutput', false, false, true);
> 
> - Advance the restart_lsn of 'test' slot
> CREATE TABLE test2(a int);
> INSERT INTO test2 SELECT generate_series(1,10000,1);
> SELECT slot_name FROM pg_replication_slot_advance('test', pg_current_wal_lsn());
> 
> - re-create the test slot but based on the old isolation_slot.
> SELECT pg_drop_replication_slot('test');
> SELECT 'copy' FROM pg_copy_logical_replication_slot('isolation_slot', 'test');
> 
> Then the restart_lsn of 'test' slot will go backwards.

Yeah, that's right.

BTW, I think it's worth to add those "corner cases" in the TAP tests related to
the sync slot feature (the more coverage the better).

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).