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: Amit Kapila <amit.kapila16@gmail.com>
Cc: "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.com>, shveta malik <shveta.malik@gmail.com>, Peter Smith <smithpb2250@gmail.com>, Ajin Cherian <itsajin@gmail.com>, Dilip Kumar <dilipbalaut@gmail.com>, Nisha Moond <nisha.moond412@gmail.com>, "Hayato Kuroda (Fujitsu)" <kuroda.hayato@fujitsu.com>, Bertrand Drouvot <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>, Alvaro Herrera <alvherre@alvh.no-ip.org>
Date: 2024-03-06T04:38:04Z
Lists: pgsql-hackers 
On Wed, Mar 6, 2024 at 12:47 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
>
> On Wed, Mar 6, 2024 at 7:36 AM Masahiko Sawada <sawada.mshk@gmail.com> wrote:
> >
> > On Tue, Mar 5, 2024 at 4:21 PM Zhijie Hou (Fujitsu)
> > <houzj.fnst@fujitsu.com> wrote:
> >
> > I have one question about PhysicalWakeupLogicalWalSnd():
> >
> > +/*
> > + * Wake up the logical walsender processes with logical failover slots if the
> > + * currently acquired physical slot is specified in standby_slot_names GUC.
> > + */
> > +void
> > +PhysicalWakeupLogicalWalSnd(void)
> > +{
> > +        List      *standby_slots;
> > +
> > +        Assert(MyReplicationSlot && SlotIsPhysical(MyReplicationSlot));
> > +
> > +        standby_slots = GetStandbySlotList();
> > +
> > +        foreach_ptr(char, name, standby_slots)
> > +        {
> > +                if (strcmp(name, NameStr(MyReplicationSlot->data.name)) == 0)
> > +                {
> > +
> > ConditionVariableBroadcast(&WalSndCtl->wal_confirm_rcv_cv);
> > +                        return;
> > +                }
> > +        }
> > +}
> >
> > IIUC walsender calls this function every time after updating the
> > slot's restart_lsn, which could be very frequently. I'm concerned that
> > it could be expensive to do a linear search on the standby_slot_names
> > list every time. Is it possible to cache the information in walsender
> > local somehow?
> >
>
> We can cache this information for WalSender but not for the case where
> users use pg_physical_replication_slot_advance(). We don't expect this
> list to be long enough to matter, so we can leave this optimization
> for the future especially if we encounter any such case unless you
> think otherwise.

Okay, agreed.

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).