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: shveta malik <shveta.malik@gmail.com>
Cc: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>, Ajin Cherian <itsajin@gmail.com>, Amit Kapila <amit.kapila16@gmail.com>, Peter Smith <smithpb2250@gmail.com>, Masahiko Sawada <sawada.mshk@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: 2024-04-29T11:58:09Z
Lists: pgsql-hackers

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On Monday, April 29, 2024 5:11 PM shveta malik <shveta.malik@gmail.com> wrote:
> 
> On Mon, Apr 29, 2024 at 11:38 AM shveta malik <shveta.malik@gmail.com>
> wrote:
> >
> > On Mon, Apr 29, 2024 at 10:57 AM Zhijie Hou (Fujitsu)
> > <houzj.fnst@fujitsu.com> wrote:
> > >
> > > On Friday, March 15, 2024 10:45 PM Bertrand Drouvot
> <bertranddrouvot.pg@gmail.com> wrote:
> > > >
> > > > Hi,
> > > >
> > > > On Thu, Mar 14, 2024 at 02:22:44AM +0000, Zhijie Hou (Fujitsu) wrote:
> > > > > Hi,
> > > > >
> > > > > Since the standby_slot_names patch has been committed, I am
> > > > > attaching the last doc patch for review.
> > > > >
> > > >
> > > > Thanks!
> > > >
> > > > 1 ===
> > > >
> > > > +   continue subscribing to publications now on the new primary
> > > > + server
> > > > without
> > > > +   any data loss.
> > > >
> > > > I think "without any data loss" should be re-worded in this
> > > > context. Data loss in the sense "data committed on the primary and
> > > > not visible on the subscriber in case of failover" can still occurs (in case
> synchronous replication is not used).
> > > >
> > > > 2 ===
> > > >
> > > > +   If the result (<literal>failover_ready</literal>) of both above steps is
> > > > +   true, existing subscriptions will be able to continue without data
> loss.
> > > > +  </para>
> > > >
> > > > I don't think that's true if synchronous replication is not used.
> > > > Say,
> > > >
> > > > - synchronous replication is not used
> > > > - primary is not able to reach the standby anymore and
> > > > standby_slot_names is set
> > > > - new data is inserted into the primary
> > > > - then not replicated to subscriber (due to standby_slot_names)
> > > >
> > > > Then I think the both above steps will return true but data would
> > > > be lost in case of failover.
> > >
> > > Thanks for the comments, attach the new version patch which reworded
> > > the above places.
> >
> > Thanks for the patch.
> >
> > Few comments:
> >
> > 1)  Tested the steps, one of the queries still refers to
> > 'conflict_reason'. I think it should refer 'conflicting'.

Thanks for catching this. Fixed.

> >
> > 2) Will it be good to mention that in case of planned promotion, it is
> > recommended to run  pg_sync_replication_slots() as last sync attempt
> > before we run failvoer-ready validation steps? This can be mentioned
> > in high-availaibility.sgml of current patch
> 
> I recall now that with the latest fix, we cannot run
> pg_sync_replication_slots() unless we disable the slot-sync worker.
> Considering that, I think it will be too many steps just to run the SQL function at
> the end without much value added. Thus we can skip this point, we can rely on
> slot sync worker completely.

Agreed. I didn't change this.

Here is the V3 doc patch.

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).