Horton

RE: Synchronizing slots from primary to standby

Zhijie Hou (Fujitsu) <houzj.fnst@fujitsu.com>

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From: "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.com>
To: "Drouvot, Bertrand" <bertranddrouvot.pg@gmail.com>, Amit Kapila <amit.kapila16@gmail.com>, shveta malik <shveta.malik@gmail.com>
Cc: Nisha Moond <nisha.moond412@gmail.com>, Peter Smith <smithpb2250@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: 2023-12-12T09:46:05Z
Lists: pgsql-hackers

Attachments

On Monday, December 11, 2023 3:52 PM Drouvot, Bertrand <bertranddrouvot.pg@gmail.com> wrote:

Hi,

> On 12/8/23 10:06 AM, Amit Kapila wrote:
> > On Wed, Dec 6, 2023 at 4:53 PM shveta malik <shveta.malik@gmail.com>
> wrote:
> >>
> >> PFA v43, changes are:
> >>
> >
> > I wanted to discuss 0003 patch about cascading standby's. It is not
> > clear to me whether we want to allow physical standbys to further wait
> > for cascading standby to sync their slots. If we allow such a feature
> > one may expect even primary to wait for all the cascading standby's
> > because otherwise still logical subscriber can be ahead of one of the
> > cascading standby.
> 
> I've the same feeling here. I think it would probably be expected that the
> primary also wait for all the cascading standby.
> 
> > I feel even if we want to allow such a behaviour we can do it later
> > once the main feature is committed.
> 
> Agree.
> 
> > I think it would
> > be good to just allow logical walsenders on primary to wait for
> > physical standbys represented by GUC 'standby_slot_names'.
> 
> That makes sense for me for v1.
> 
> > If we agree
> > on that then it would be good to prohibit setting this GUC on standby
> > or at least it should be a no-op even if this GUC should be set on
> > physical standby.
> 
> I'd prefer to completely prohibit it on standby (to make it very clear it's not
> working at all) as long as one can enable it without downtime once the standby
> is promoted (which is the case currently).

I think we could not check if we are in a standby server in the GUC check_hook,
because the XLogCtl(which is checked in RecoveryInProgress) may have not been
initialized yet. Besides, other GUCs like synchronous_standby_names also don't
work on standby but it will be no-op. So I feel we can also ignore
standby_slot_names on standby. What do you think ?

Here is the V46 patch set which changed the following things:

V46-0001:
* Address Peter[1] and Amit's[2] comments.
* Fix one CFbot failure in meson build.
* Ignore the standby_slot_names on a standby server since we don't support
  syncing slots to cascade standby.

V46-0002:
1) Fix for CFBot make warning.
2) Cascading support removal. Now we do not need to check 'sync_state != 'i''
   in the query while fetching failover slots. This check was needed on the
   cascading standby to fetch failover slots from the first standby.
3) Test correction and optimization.

0003 patch is removed since we agreed not to support syncing slots to cascading
standby.

Thanks Shveta for working on the changes in V46-0002 and thanks Ajin for
working on the test optimization.

--
TODO

There are few pending comments that mentioned in [3][4][5] which are still in
progress.

[1] https://www.postgresql.org/message-id/CAHut%2BPsf9z132WNgy0Gr10ZTnonpNjvTBj74wG8kSxXU4rOD7g%40mail.gmail.com
[2] https://www.postgresql.org/message-id/CAA4eK1%2BCXpfiTLbYRaOoUBP9Z1-xJZdX6QOp14rCdaF5E2gsgQ%40mail.gmail.com
[3] https://www.postgresql.org/message-id/CAJpy0uDaGMNpgmdxie-MgHmMhnD4ET_LDjQNEe76xJ%2BMLqRQ8Q%40mail.gmail.com
[4] https://www.postgresql.org/message-id/CAJpy0uDcOf5Hvk_CdCCAbfx9SY%2Bog%3D%3D%3DtgiuhWKzkYyqebui9g%40mail.gmail.com
[5] https://www.postgresql.org/message-id/CAJpy0uC-8mrn6jakcFjSVmbJiHZs-Okq8YKxGfrMLPD-2%3DwOqQ%40mail.gmail.com

Best Regards,
Hou zj

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).