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: Peter Smith <smithpb2250@gmail.com>
Cc: "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.com>, Amit Kapila <amit.kapila16@gmail.com>, shveta malik <shveta.malik@gmail.com>, Masahiko Sawada <sawada.mshk@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: 2024-02-27T10:37:40Z
Lists: pgsql-hackers 
Hi,

On Tue, Feb 27, 2024 at 06:17:44PM +1100, Peter Smith wrote:
> +static bool
> +validate_standby_slots(char **newval)
> +{
> + char    *rawname;
> + List    *elemlist;
> + ListCell   *lc;
> + bool ok;
> +
> + /* Need a modifiable copy of string */
> + rawname = pstrdup(*newval);
> +
> + /* Verify syntax and parse string into a list of identifiers */
> + ok = SplitIdentifierString(rawname, ',', &elemlist);
> +
> + if (!ok)
> + {
> + GUC_check_errdetail("List syntax is invalid.");
> + }
> +
> + /*
> + * If the replication slots' data have been initialized, verify if the
> + * specified slots exist and are logical slots.
> + */
> + else if (ReplicationSlotCtl)
> + {
> + foreach(lc, elemlist)
> 
> 6a.
> So, if the ReplicationSlotCtl is NULL, it is possible to return
> ok=true without ever checking if the slots exist or are of the correct
> kind. I am wondering what are the ramifications of that. -- e.g.
> assuming names are OK when maybe they aren't OK at all. AFAICT this
> works because it relies on getting subsequent WARNINGS when calling
> FilterStandbySlots(). If that is correct then maybe the comment here
> can be enhanced to say so.
> 
> Indeed, if it works like that, now I am wondering do we need this for
> loop validation at all. e.g. it seems just a matter of timing whether
> we get ERRORs validating the GUC here, or WARNINGS later in the
> FilterStandbySlots. Maybe we don't need the double-checking and it is
> enough to check in FilterStandbySlots?

Good point, I have the feeling that it is enough to check in FilterStandbySlots().

Indeed, if the value is syntactically correct, then I think that its actual value
"really" matters when the logical decoding is starting/running, does it provide
additional benefits "before" that?

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).