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: "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.com>, "Drouvot, Bertrand" <bertranddrouvot.pg@gmail.com>, Peter Smith <smithpb2250@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>, shveta malik <shveta.malik@gmail.com>
Date: 2023-11-07T11:25:05Z
Lists: pgsql-hackers

Attachments

On Mon, Nov 6, 2023 at 5:36 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
>
> On Mon, Nov 6, 2023 at 1:57 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
> >
> > On Mon, Nov 6, 2023 at 7:01 AM Zhijie Hou (Fujitsu)
> > <houzj.fnst@fujitsu.com> wrote:
> > >
>
> +static void
> +WalSndGetStandbySlots(List **standby_slots, bool force)
> +{
> + if (!MyReplicationSlot->data.failover)
> + return;
> +
> + if (standby_slot_names_list == NIL && strcmp(standby_slot_names, "") != 0)
> + SlotSyncInitConfig();
> +
> + if (force || StandbySlotNamesPreReload == NULL ||
> + strcmp(StandbySlotNamesPreReload, standby_slot_names) != 0)
> + {
> + list_free(*standby_slots);
> +
> + if (StandbySlotNamesPreReload)
> + pfree(StandbySlotNamesPreReload);
> +
> + StandbySlotNamesPreReload = pstrdup(standby_slot_names);
> + *standby_slots = list_copy(standby_slot_names_list);
> + }
> +}
>
> I find this code bit difficult to understand. I think we don't need to
> maintain a global variable like StandbySlotNamesPreReload. We can use
> a local variable for it on the lines of what we do in
> StartupRereadConfig(). Then, can we think of maintaining
> standby_slot_names_list in something related to decoding like
> LogicalDecodingContext as this will be used during decoding only?
>

Yes, agreed. This code part is now simplified in v31. PFA the patches.

The overall changes are:

1) Caching of the standby_slots list in the logical-decoding context
as suggested above. All the globals have been removed.
2) Dropping of local synced slots for obsolete dbs. Launcher now takes
care of that.
3) There was a repeated warning in the log file due to missing GUCs as
described in [1]. Fixed that.
4) Optimized code in slotsync.c and launcher.c to get rid of globals.
5) Adjusted patch003's wait-for-standby logic in slot-sync workers as
per changes in pt. 1. There is still one optimization left here (in
patch003) to avoid repeated parsing. I have mentioned the TODO
comment. Will be targeted in the next version.

The changes for 1 are in patch01. The changes for 2,3,4 are in patch02.

Thanks Hou-san for implementing the changes for 1 and assisting in 5.

[1]: https://www.postgresql.org/message-id/CAJpy0uDpV0suPbhCp%2B1aRLXEChD9uKp-ffBW_HfZro%3D53JKK5w%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).