Horton

Re: Synchronizing slots from primary to standby

Amit Kapila <amit.kapila16@gmail.com>

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From: Amit Kapila <amit.kapila16@gmail.com>
To: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
Cc: shveta malik <shveta.malik@gmail.com>, Masahiko Sawada <sawada.mshk@gmail.com>, "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.com>, Dilip Kumar <dilipbalaut@gmail.com>, Peter Smith <smithpb2250@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>, Ajin Cherian <itsajin@gmail.com>, Alvaro Herrera <alvherre@alvh.no-ip.org>
Date: 2024-01-22T09:40:26Z
Lists: pgsql-hackers 
On Mon, Jan 22, 2024 at 1:11 PM Bertrand Drouvot
<bertranddrouvot.pg@gmail.com> wrote:
>
> Hi,
>

Thanks for sharing the feedback.

>
> > Then we also discussed whether extending libpqwalreceiver's connect
> > API is a good idea and whether we need to further extend it in the
> > future. As far as I can see, slotsync worker's primary requirement is
> > to execute SQL queries which the current API is sufficient, and don't
> > see something that needs any drastic change in this API. Note that
> > tablesync worker that executes SQL also uses these APIs, so we may
> > need something in the future for either of those. Then finally we need
> > a slotsync worker to also connect to a database to use SQL and fetch
> > results.
> >
>
> On my side the nits concerns about using the libpqrcv_connect / walrcv_connect are:
>
> - cosmetic: the "rcv" do not really align with the sync slot worker
>

But note that the same API is even used for apply worker as well. One
can think that this is a connection used to receive WAL or slot_info.

minor comments on the patch:
=======================
1.
+ /* First time slot update, the function must return true */
+ Assert(local_slot_update(remote_slot));

Isn't moving this code to Assert in update_and_persist_slot() wrong?
It will make this function call no-op in non-assert builds?

2.
+ ereport(LOG,
+ errmsg("newly locally created slot \"%s\" is sync-ready now",

I think even without 'locally' in the above LOG message, it is clear.

3.
+/*
+ * walrcv_get_dbinfo_for_failover_slots_fn
+ *
+ * Run LIST_DBID_FOR_FAILOVER_SLOTS on primary server to get the
+ * list of unique DBIDs for failover logical slots
+ */
+typedef List *(*walrcv_get_dbinfo_for_failover_slots_fn)
(WalReceiverConn *conn);

This looks like a leftover from the previous version of the patch.

-- 
With Regards,
Amit Kapila.

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).