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: Amit Kapila <amit.kapila16@gmail.com>
Cc: shveta malik <shveta.malik@gmail.com>, "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.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: 2024-01-05T08:15:46Z
Lists: pgsql-hackers 
Hi,

On Fri, Jan 05, 2024 at 10:00:53AM +0530, Amit Kapila wrote:
> On Fri, Jan 5, 2024 at 8:59 AM shveta malik <shveta.malik@gmail.com> wrote:
> >
> > On Thu, Jan 4, 2024 at 7:24 PM Bertrand Drouvot
> > <bertranddrouvot.pg@gmail.com> wrote:
> > >
> > > 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?
> >
> > I gave it a thought earlier, but then I was not sure even if I create
> > a new function w/o "rcv" in it then where should it be placed as the
> > existing file name itself is libpq'walreceiver'.c. Shall we be
> > creating a new file then? But it does not seem good to create a new
> > setup (new file, function pointers  other stuff) around 1 function.

Yeah...

> > And thus reusing the same function with 'replication' (new arg) felt
> > like a better choice than other options. If in future, there is any
> > other module trying to do the same, then it can use current
> > walrcv_connect() with rep=false. If I make it specific to slot-sync
> > worker, then it will not be reusable by other modules (if needed).

Yeah good point, it would need to be more generic.

> I agree that the benefit of creating a new API is not very clear.

Yeah, that would be more for cosmetic purpose (and avoid using a WalReceiverConn
while a PGconn could/should suffice).

> How
> about adjusting the description in the file header of
> libpqwalreceiver.c. 

Agree, that seems to be a better option (not sure that building the new API is
worth the extra work).

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).