Horton

Re: Synchronizing slots from primary to standby

Masahiko Sawada <sawada.mshk@gmail.com>

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From: Masahiko Sawada <sawada.mshk@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>, 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: 2024-03-06T06:37:00Z
Lists: pgsql-hackers 
On Fri, Mar 1, 2024 at 3:22 PM Peter Smith <smithpb2250@gmail.com> wrote:
>
> On Fri, Mar 1, 2024 at 5:11 PM Masahiko Sawada <sawada.mshk@gmail.com> wrote:
> >
> ...
> > +        /*
> > +         * "*" is not accepted as in that case primary will not be able to know
> > +         * for which all standbys to wait for. Even if we have physical slots
> > +         * info, there is no way to confirm whether there is any standby
> > +         * configured for the known physical slots.
> > +         */
> > +        if (strcmp(*newval, "*") == 0)
> > +        {
> > +                GUC_check_errdetail("\"*\" is not accepted for
> > standby_slot_names");
> > +                return false;
> > +        }
> >
> > Why only '*' is checked aside from validate_standby_slots()? I think
> > that the doc doesn't mention anything about '*' and '*' cannot be used
> > as a replication slot name. So even if we don't have this check, it
> > might be no problem.
> >
>
> Hi, a while ago I asked this same question. See [1 #28] for the response..

Thanks. Quoting the response from the email:

SplitIdentifierString() does not give error for '*' and '*' can be considered
as valid value which if accepted can mislead user that all the standbys's slots
are now considered, which is not the case here. So we want to explicitly call
out this case i.e. '*' is not accepted as valid value for standby_slot_names.

IIUC we're concerned with a case like where the user confused
standby_slot_names values with synchronous_standby_names values. Which
means we would need to keep thath check consistent with available
values of synchronous_standby_names. For example, if we support a
regexp for synchronous_standby_names, we will have to update the check
so we disallow other special characters. Also, if we add a new
replication-related parameter that accepts other special characters as
the value in the future, will we want to raise an error also for such
values in check_standby_slot_names()?

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).