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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: Amit Kapila <amit.kapila16@gmail.com>, Masahiko Sawada <sawada.mshk@gmail.com>, "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.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>, 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: 2024-02-23T07:51:43Z
Lists: pgsql-hackers 
Hi,

On Fri, Feb 23, 2024 at 08:35:44AM +0530, shveta malik wrote:
> On Thu, Feb 22, 2024 at 4:35 PM Bertrand Drouvot
> <bertranddrouvot.pg@gmail.com> wrote:
> >
> > Suppose that in synchronize_slots() the query would be:
> >
> >     const char *query = "SELECT slot_name, plugin, confirmed_flush_lsn,"
> >         " restart_lsn, catalog_xmin, two_phase, failover,"
> >         " database, conflict_reason"
> >         " FROM pg_catalog.pg_replication_slots"
> >         " WHERE failover and NOT temporary and 1 = 1";
> >
> > Then my comment is to rewrite it to:
> >
> >     const char *query = "SELECT slot_name, plugin, confirmed_flush_lsn,"
> >         " restart_lsn, catalog_xmin, two_phase, failover,"
> >         " database, conflict_reason"
> >         " FROM pg_catalog.pg_replication_slots"
> >         " WHERE failover and NOT temporary and 1 OPERATOR(pg_catalog.=) 1";
> >
> > to ensure the operator "=" is coming from the pg_catalog schema.
> >
> 
> Thanks for the details, but slot-sync does not use SPI calls, it uses
> libpqrcv calls.

Sorry for the confusion, I meant to say "remote SQL calls".

> So is this change needed?

The example I provided is a "fake" one (as currently the "=" operator is not
used in the const char *query in synchronize_slots()). So there is currently
nothing to change here. I just want to highlight that if we are using (or will
use) operators in the remote SQL calls then we should ensure they are coming from
the pg_catalog schema (as in the example provided above).

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).