Horton

Re: Synchronizing slots from primary to standby

Bertrand Drouvot <bertranddrouvot.pg@gmail.com>

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From: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
To: shveta malik <shveta.malik@gmail.com>
Cc: "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.com>, Amit Kapila <amit.kapila16@gmail.com>, Masahiko Sawada <sawada.mshk@gmail.com>, Peter Smith <smithpb2250@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>, Ajin Cherian <itsajin@gmail.com>, Alvaro Herrera <alvherre@alvh.no-ip.org>
Date: 2024-01-04T13:54:44Z
Lists: pgsql-hackers 
Hi,

On Thu, Jan 04, 2024 at 10:27:31AM +0530, shveta malik wrote:
> On Thu, Jan 4, 2024 at 9:18 AM shveta malik <shveta.malik@gmail.com> wrote:
> >
> > On Wed, Jan 3, 2024 at 6:33 PM Zhijie Hou (Fujitsu)
> > <houzj.fnst@fujitsu.com> wrote:
> > >
> > > On Tuesday, January 2, 2024 6:32 PM shveta malik <shveta.malik@gmail.com> wrote:
> > > > On Fri, Dec 29, 2023 at 10:25 AM Amit Kapila <amit.kapila16@gmail.com>
> > > >
> > > > The topup patch has also changed app_name to
> > > > {cluster_name}_slotsyncworker so that we do not confuse between walreceiver
> > > > and slotsyncworker entry.
> > > >
> > > > Please note that there is no change in rest of the patches, changes are in
> > > > additional 0004 patch alone.
> > >
> > > Attach the V56 patch set which supports ALTER SUBSCRIPTION SET (failover).
> > > This is useful when user want to refresh the publication tables, they can now alter the
> > > failover option to false and then execute the refresh command.
> > >
> > > Best Regards,
> > > Hou zj
> >
> > The patches no longer apply to HEAD due to a recent commit 007693f. I
> > am working on rebasing and will post the new patches soon
> >
> > thanks
> > Shveta
> 
> Commit 007693f has changed 'conflicting' to 'conflict_reason', so
> adjusted the code around that in the slotsync worker.
> 
> Also removed function 'pg_get_slot_invalidation_cause' as now
> conflict_reason tells the same.
> 
> PFA rebased patches with above changes.
> 

Thanks!

Looking at 0004:

1 ====

-libpqrcv_connect(const char *conninfo, bool logical, bool must_use_password,
-                                const char *appname, char **err)
+libpqrcv_connect(const char *conninfo, bool replication, bool logical,
+                                bool must_use_password, const char *appname, char **err)

What about adjusting the preceding comment a bit to describe what the new replication
parameter is for?

2 ====

+       /* We can not have logical w/o replication */

what about replacing w/o by without?

3 ===

+       if(!replication)
+               Assert(!logical);
+
+       if (replication)
        {

what about using "if () else" instead (to avoid unnecessary test)?


Having said that the patch seems a reasonable way to implement non-replication
connection in slotsync worker.

4 ===

Looking closer, the only place where walrcv_connect() is called with replication
set to false and logical set to false is in ReplSlotSyncWorkerMain().

That does make sense, but what do you think about creating dedicated libpqslotsyncwrkr_connect
and slotsyncwrkr_connect (instead of using the libpqrcv_connect / walrcv_connect ones)?

That way we could make use of slotsyncwrkr_connect() in ReplSlotSyncWorkerMain()
as I think it's confusing to use "rcv" functions while the process using them is
not of backend type walreceiver.

I'm not sure that worth the extra complexity though, what do you think?

Regards,

-- 
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
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).