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: "Drouvot, Bertrand" <bertranddrouvot.pg@gmail.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>, Dilip Kumar <dilipbalaut@gmail.com>, shveta malik <shveta.malik@gmail.com>
Date: 2023-09-06T08:37:20Z
Lists: pgsql-hackers

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On Wed, Aug 30, 2023 at 9:29 AM shveta malik <shveta.malik@gmail.com> wrote:
>
>
> PFA new patch-set which attempts to fix these:
>


PFA v15 which implements below changes:

1) It parses synchronize_slot_names and standby_slot_names and caches
the list to avoid repeated parsing. This parsing is done at Walsender
startup on primary and slot-sync worker startup on standby and then
during each SIGHUP.

2) Handles slots invaliation:
2.1) If the slot is invalidated on primary, it is now invalidated on
standby as well. Standby gets invalidation info from primary using a
new system function 'pg_get_invalidation_cause(slotname)'.
2.2) if the slot is invalidated on standby alone, it is dropped and
recreated as per synchronize_slot_names in next sync-cycle.

3) The test file 051_slot_sync.pl is removed from patch2 for the
time-being. It was testing whether the logical slot on standby is
conflicted or not once slot on primary is removed by 'Drop
Subscription' and WALs needed by logical slot on standby are flushed
on primary (with hot_standby_feedback=off). But as per current
implementation, we drop the slot on standby as soon as subscription is
dropped on primary. So the testcase no longer solves the purpose for
which it was added. Correct set of test cases will be added going
forward.

4) Address most of the comments by Peter.

Change 1 is in patch01 along with patch02, rest are in patch02 alone.

Thank You Ajin for assisting on the above changes.

Next in the pipeline:
1) Currently it allows specifying logical slots in standby_slot_names.
This should be prohibited.
2) We need to ensure that WAL is replayed on standby before moving the
slot's position to the target location received from the primary.
3) Rest of the comments upthread.

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).