Horton

Re: Synchronizing slots from primary to standby

Ajin Cherian <itsajin@gmail.com>

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From: Ajin Cherian <itsajin@gmail.com>
To: shveta malik <shveta.malik@gmail.com>
Cc: Amit Kapila <amit.kapila16@gmail.com>, Bertrand Drouvot <bertranddrouvot.pg@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>, Alvaro Herrera <alvherre@alvh.no-ip.org>
Date: 2024-01-23T09:07:50Z
Lists: pgsql-hackers 
On Mon, Jan 22, 2024 at 10:30 PM shveta malik <shveta.malik@gmail.com>
wrote:
>
> On Mon, Jan 22, 2024 at 3:10 PM Amit Kapila <amit.kapila16@gmail.com>
wrote:
> >
> > minor comments on the patch:
> > =======================
>
> PFA v65 addressing the comments.
>
> Addressed comments by Peter in [1], comments by Hou-San in [2],
> comments by Amit in [3] and [4]
>
> TODO:
> Analyze the issue reported by Swada-san in [5] (pt 2)
> Disallow subscription creation on standby with failover=true (as we do
> not support sync on cascading standbys)
>
> [1]:
https://www.postgresql.org/message-id/CAHut%2BPt5Pk_xJkb54oahR%2Bf9oawgfnmbpewvkZPgnRhoJ3gkYg%40mail.gmail.com
> [2]:
https://www.postgresql.org/message-id/OS0PR01MB57160C7184E17C6765AAE38294752%40OS0PR01MB5716.jpnprd01.prod.outlook.com
> [3]:
https://www.postgresql.org/message-id/CAA4eK1JPB-zpGYTbVOP5Qp26tNQPMjDuYzNZ%2Ba9RFiN5nE1tEA%40mail.gmail.com
> [4]:
https://www.postgresql.org/message-id/CAA4eK1Jhy1-bsu6vc0%3DNja7aw5-EK_%3D101pnnuM3ATqTA8%2B%3DSg%40mail.gmail.com
> [5]:
https://www.postgresql.org/message-id/CAD21AoBgzONdt3o5mzbQ4MtqAE%3DWseiXUOq0LMqne-nWGjZBsA%40mail.gmail.com
>
>
I was doing some testing on this. What I noticed is that creating
subscriptions with failover enabled is taking a lot longer compared with a
subscription with failover disabled. The setup has primary configured with
standby_slot_names and that standby is enabled with enable_synclot turned
on.

Publisher has one publication, no tables.
subscriber:
postgres=# \timing
Timing is on.
postgres=# CREATE SUBSCRIPTION sub CONNECTION 'dbname=postgres
host=localhost port=6972' PUBLICATION pub with (failover = true);
NOTICE:  created replication slot "sub" on publisher
CREATE SUBSCRIPTION
Time: 10011.829 ms (00:10.012)

== drop the sub

postgres=# CREATE SUBSCRIPTION sub CONNECTION 'dbname=postgres
host=localhost port=6972' PUBLICATION pub with (failover = false);
NOTICE:  created replication slot "sub" on publisher
CREATE SUBSCRIPTION
Time: 46.317 ms

With failover=true, it takes 10011 ms while failover=false takes 46 ms.

I don't see a similar delay when creating slot on the primary with
pg_create_logical_replication_slot() with failover flag enabled.

Then on primary:
postgres=# SELECT 'init' FROM
pg_create_logical_replication_slot('lsub2_slot', 'pgoutput', false, false,
true);
?column?
----------
init
(1 row)

Time: 36.125 ms
postgres=# SELECT 'init' FROM
pg_create_logical_replication_slot('lsub1_slot', 'pgoutput', false, false,
false);
?column?
----------
init
(1 row)

Time: 53.981 ms

regards,
Ajin Cherian
Fujitsu Australia

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).