Horton

Re: Synchronizing slots from primary to standby

Masahiko Sawada <sawada.mshk@gmail.com>

View thread View on postgr.es
From: Masahiko Sawada <sawada.mshk@gmail.com>
To: "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.com>
Cc: shveta malik <shveta.malik@gmail.com>, Peter Smith <smithpb2250@gmail.com>, Amit Kapila <amit.kapila16@gmail.com>, Ajin Cherian <itsajin@gmail.com>, Bertrand Drouvot <bertranddrouvot.pg@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: 2024-02-10T12:00:45Z
Lists: pgsql-hackers 
On Fri, Feb 9, 2024 at 4:08 PM Zhijie Hou (Fujitsu)
<houzj.fnst@fujitsu.com> wrote:
>
> On Friday, February 9, 2024 2:44 PM Masahiko Sawada <sawada.mshk@gmail.com> wrote:
> >
> > On Thu, Feb 8, 2024 at 8:01 PM shveta malik <shveta.malik@gmail.com> wrote:
> > >
> > > On Thu, Feb 8, 2024 at 12:08 PM Peter Smith <smithpb2250@gmail.com>
> > wrote:
> > > >
> > > > Here are some review comments for patch v80_2-0001.
> > >
> > > Thanks for the feedback Peter. Addressed the comments in v81.
> > > Attached patch001 for early feedback. Rest of the patches need
> > > rebasing and thus will post those later.
> > >
> > > It also addresses comments by Amit in [1].
> >
> > Thank you for updating the patch! Here are random comments:
>
> Thanks for the comments!
>
> >
> > ---
> > +
> > +        /*
> > +         * Register the callback function to clean up the shared memory of
> > slot
> > +         * synchronization.
> > +         */
> > +        SlotSyncInitialize();
> >
> > I think it would have a wider impact than expected. IIUC this callback is needed
> > only for processes who calls synchronize_slots(). Why do we want all processes
> > to register this callback?
>
> I think the current style is similar to the ReplicationSlotInitialize() above it. For backend,
> both of them can only be used when user calls slot SQL functions. So, I think it could be fine to
> register it at the general place which can also avoid registering the same again for the later
> slotsync worker patch.

Yes, but it seems to be a legitimate case since replication slot code
involves many functions that need the callback to clear the flag. On
the other hand, in the slotsync code, only one function,
SyncReplicationSlots(), needs the callback at least in 0001 patch.

> Another alternative is to register the callback when calling slotsync functions
> and unregister it after the function call. And register the callback in
> slotsyncworkmain() for the slotsync worker patch, although this may adds a few
> more codes.

Another idea is that SyncReplicationSlots() calls synchronize_slots()
in PG_ENSURE_ERROR_CLEANUP() block instead of PG_TRY(), to make sure
to clear the flag in case of ERROR or FATAL. And the slotsync worker
uses the before_shmem_callback to clear the flag.

Regards,

-- 
Masahiko Sawada
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).