Horton

Re: Synchronizing slots from primary to standby

shveta malik <shveta.malik@gmail.com>

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From: shveta malik <shveta.malik@gmail.com>
To: Amit Kapila <amit.kapila16@gmail.com>
Cc: Peter Smith <smithpb2250@gmail.com>, "Drouvot, Bertrand" <bertranddrouvot.pg@gmail.com>, Nisha Moond <nisha.moond412@gmail.com>, "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.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>, shveta malik <shveta.malik@gmail.com>
Date: 2023-12-19T11:40:57Z
Lists: pgsql-hackers

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On Tue, Dec 19, 2023 at 11:37 AM Amit Kapila <amit.kapila16@gmail.com> wrote:
>
> On Tue, Dec 19, 2023 at 4:51 AM Peter Smith <smithpb2250@gmail.com> wrote:
> >
> >
> > ======
> > doc/src/sgml/system-views.sgml
> >
> > 3.
> > +      <para>
> > +      The hot standby can have any of these sync_state values for the slots but
> > +      on a hot standby, the slots with state 'r' and 'i' can neither be used
> > +      for logical decoding nor dropped by the user.
> > +      The sync_state has no meaning on the primary server; the primary
> > +      sync_state value is default 'n' for all slots but may (if leftover
> > +      from a promoted standby)  also be 'r'.
> > +      </para></entry>
> >
> > I still feel we are exposing too much useless information about the
> > primary server values.
> >
> > Isn't it sufficient to just say "The sync_state values have no meaning
> > on a primary server.", and not bother to mention what those
> > meaningless values might be -- e.g. if they are meaningless then who
> > cares what they are or how they got there?
> >
>
> I feel it would be good to mention somewhere that primary can have
> slots in 'r' state, if not here, some other place.
>
> >
> > 7.
> > +/*
> > + * Exit the slot sync worker with given exit-code.
> > + */
> > +static void
> > +slotsync_worker_exit(const char *msg, int code)
> > +{
> > + ereport(LOG, errmsg("%s", msg));
> > + proc_exit(code);
> > +}
> >
> > This could be written differently (don't pass the exit code, instead
> > pass a bool) like:
> >
> > static void
> > slotsync_worker_exit(const char *msg, bool restart_worker)
> >
> > By doing it this way, you can keep the special exit code values (0,1)
> > within this function where you can comment all about them instead of
> > having scattered comments about exit codes in the callers.
> >
> > SUGGESTION
> > ereport(LOG, errmsg("%s", msg));
> > /* <some big comment here about how the code causes the worker to
> > restart or not> */
> > proc_exit(restart_worker ? 1 : 0);
> >
>
> Hmm, I don't see the need for this function in the first place. We can
> use proc_exit in the two callers directly.
>
> --
> With Regards,
> Amit Kapila.


PFA v50 patch-set which addresses comments for  v48-0002 and v49-0002
given in [1], [2] and [3].

TODO:
--Fix CFBot failure.
--Work on correctness of test to merge patch003 to patch002

[1]: https://www.postgresql.org/message-id/CAA4eK1Ko-EBBDkea2R8V8PeveGg10PBswCF7JQdnRu%2BMJP%2BYBQ%40mail.gmail.com
[2]: https://www.postgresql.org/message-id/CAHut%2BPsyZQZ1A4XcKw-D%3DvcTg16pN9Dw0PzE8W_X7Yz_bv00rQ%40mail.gmail.com
[3]: https://www.postgresql.org/message-id/CAHut%2BPv86wBZiyOLHxycd8Yj9%3Dk5kzVa1x7Gbp%2B%3Dc1VGT9TG2w%40mail.gmail.com


thanks
Shveta

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).