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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: Peter Smith <smithpb2250@gmail.com>
Cc: "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.com>, Masahiko Sawada <sawada.mshk@gmail.com>, Amit Kapila <amit.kapila16@gmail.com>, Ajin Cherian <itsajin@gmail.com>, Bertrand Drouvot <bertranddrouvot.pg@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>, shveta malik <shveta.malik@gmail.com>
Date: 2024-02-07T09:32:40Z
Lists: pgsql-hackers

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On Wed, Feb 7, 2024 at 9:30 AM Peter Smith <smithpb2250@gmail.com> wrote:
>
> Here are some review comments for v79-0001

Thanks for the feedback. Addressed the comments in v80 patch-set.
Please find my response inline for few.

> src/sgml/logicaldecoding.sgml
> 3.
> +   <sect2 id="logicaldecoding-replication-slots-synchronization">
> +    <title>Replication Slot Synchronization</title>
> +    <para>
> +     A logical replication slot on the primary can be synchronized to the hot
> +     standby by enabling the <literal>failover</literal> option for the slot
> +     and calling <function>pg_sync_replication_slots</function>
> +     on the standby. The <literal>failover</literal> option of the slot
> +     can be enabled either by enabling
> +     <link linkend="sql-createsubscription-params-with-failover">
> +     <literal>failover</literal></link>
> +     option during subscription creation or by providing
> <literal>failover</literal>
> +     parameter during
> +     <link linkend="pg-create-logical-replication-slot">
> +     <function>pg_create_logical_replication_slot</function></link>.
>
> IMO it will be better to slightly reword this (like was suggested for
> the Commit Message). I felt it is also better to refer/link to "CREATE
> SUBSCRIPTION" instead of saying "during subscription creation".

Regarding link to create-sub, the
'sql-createsubscription-params-with-failover' takes you to the
failover property of Create-Subscription page. Won't that suffice?

>
> 8.
> +/*
> + * Register the callback function to clean up the shared memory of slot
> + * synchronization.
> + */
> +void
> +SlotSyncInitialize(void)
> +{
> + before_shmem_exit(SlotSyncShmemExit, 0);
> +}
>
> This is only doing registration for cleanup of shmem stuff. So, does
> it really need it to be a separate function, or can this be registered
> within SlotSyncShmemInit() itself?

I think it makes more sense to call it from BaseInit() where we have
all such calls like InitTemporaryFileAccess(),
ReplicationSlotInitialize() etc which do similar callback
registrations using before_shmem_exit().

Attached the patches for v80. Overall changes are:

--Addressed comments by Peter (which I responded above) and Amit given
in [1] and [2].
--Also improved commit msg and comment around 'wal_level' as suggested
by Bertrand in [3].

[1]: https://www.postgresql.org/message-id/CAHut%2BPvtysbVd8tj2AADk%3DeNo0VY9Ov9wkBP-K%2B9tj1wRS4M4w%40mail.gmail.com
[2]: https://www.postgresql.org/message-id/CAA4eK1%2Bar0N1xXnZZ26BG1qO4LHRS8v3wnH9Pnz4BWmk6SDTHw%40mail.gmail.com
[3]: https://www.postgresql.org/message-id/ZcHX4SXkqtGe27a6%40ip-10-97-1-34.eu-west-3.compute.internal

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).