Horton

Synchronizing slots from primary to standby

Peter Eisentraut <peter.eisentraut@enterprisedb.com>

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From: Peter Eisentraut <peter.eisentraut@enterprisedb.com>
To: pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2021-10-31T10:08:18Z
Lists: pgsql-hackers

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I want to reactivate $subject.  I took Petr Jelinek's patch from [0], 
rebased it, added a bit of testing.  It basically works, but as 
mentioned in [0], there are various issues to work out.

The idea is that the standby runs a background worker to periodically 
fetch replication slot information from the primary.  On failover, a 
logical subscriber would then ideally find up-to-date replication slots 
on the new publisher and can just continue normally.

The previous thread didn't have a lot of discussion, but I have gathered 
from off-line conversations that there is a wider agreement on this 
approach.  So the next steps would be to make it more robust and 
configurable and documented.  As I said, I added a small test case to 
show that it works at all, but I think a lot more tests should be added. 
  I have also found that this breaks some seemingly unrelated tests in 
the recovery test suite.  I have disabled these here.  I'm not sure if 
the patch actually breaks anything or if these are just differences in 
timing or implementation dependencies.  This patch adds a LIST_SLOTS 
replication command, but I think this could be replaced with just a 
SELECT FROM pg_replication_slots query now.  (This patch is originally 
older than when you could run SELECT queries over the replication protocol.)

So, again, this isn't anywhere near ready, but there is already a lot 
here to gather feedback about how it works, how it should work, how to 
configure it, and how it fits into an overall replication and HA 
architecture.


[0]: 
https://www.postgresql.org/message-id/flat/3095349b-44d4-bf11-1b33-7eefb585d578%402ndquadrant.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).