Horton

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: Peter Smith <smithpb2250@gmail.com>
Cc: "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.com>, Amit Kapila <amit.kapila16@gmail.com>, shveta malik <shveta.malik@gmail.com>, Masahiko Sawada <sawada.mshk@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>
Date: 2024-03-01T07:15:45Z
Lists: pgsql-hackers 
Hi,

On Fri, Mar 01, 2024 at 03:22:55PM +1100, Peter Smith wrote:
> Here are some review comments for v102-0001.
> 
> ======
> doc/src/sgml/config.sgml
> 
> 1.
> +       <para>
> +        Lists the streaming replication standby server slot names that logical
> +        WAL sender processes will wait for. Logical WAL sender processes will
> +        send decoded changes to plugins only after the specified replication
> +        slots confirm receiving WAL. This guarantees that logical replication
> +        slots with failover enabled do not consume changes until those changes
> +        are received and flushed to corresponding physical standbys. If a
> +        logical replication connection is meant to switch to a physical standby
> +        after the standby is promoted, the physical replication slot for the
> +        standby should be listed here. Note that logical replication will not
> +        proceed if the slots specified in the standby_slot_names do
> not exist or
> +        are invalidated.
> +       </para>
> 
> Should this also mention the effect this GUC has on those 2 SQL
> functions? E.g. Commit message says:
> 
> Additionally, The SQL functions pg_logical_slot_get_changes and
> pg_replication_slot_advance are modified to wait for the replication
> slots mentioned in 'standby_slot_names' to catch up before returning.

I think that's also true for all the ones that rely on
pg_logical_slot_get_changes_guts(), means:

- pg_logical_slot_get_changes
- pg_logical_slot_peek_changes
- pg_logical_slot_get_binary_changes
- pg_logical_slot_peek_binary_changes

Not sure it's worth to mention the "binary" ones though as their doc mention
they behave as their "non binary" counterpart.

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).