Horton

RE: Synchronizing slots from primary to standby

Zhijie Hou (Fujitsu) <houzj.fnst@fujitsu.com>

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From: "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.com>
To: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
Cc: shveta malik <shveta.malik@gmail.com>, Ajin Cherian <itsajin@gmail.com>, Amit Kapila <amit.kapila16@gmail.com>, Peter Smith <smithpb2250@gmail.com>, Masahiko Sawada <sawada.mshk@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>
Date: 2024-06-05T02:19:41Z
Lists: pgsql-hackers 
On Wednesday, May 8, 2024 5:21 PM Bertrand Drouvot <bertranddrouvot.pg@gmail.com> wrote:
> A few comments:
Thanks for the comments!

> 2 ===
> 
> +test_sub=# SELECT
> +               array_agg(slotname) AS slots
> +           FROM
> +           ((
> +               SELECT r.srsubid AS subid, CONCAT('pg_', srsubid, '_sync_',
> srrelid, '_', ctl.system_identifier) AS slotname
> +               FROM pg_control_system() ctl, pg_subscription_rel r,
> pg_subscription s
> +               WHERE r.srsubstate = 'f' AND s.oid = r.srsubid AND
> s.subfailover
> +           ) UNION (
> 
> I guess this format comes from ReplicationSlotNameForTablesync(). What
> about creating a SQL callable function on top of it and make use of it in the
> query above? (that would ensure to keep the doc up to date even if the format
> changes in ReplicationSlotNameForTablesync()).

We could add a new function as suggested but I think it's not the right
time(beta1) to add this function because new function will bring
catversion bump which I think may not be worth at this stage. I think we can
consider this after releasing and maybe gather more use cases for the new
function you suggested.

> 
> 3 ===
> 
> +test_sub=# SELECT
> +               MAX(remote_lsn) AS remote_lsn_on_subscriber
> +           FROM
> +           ((
> +               SELECT (CASE WHEN r.srsubstate = 'f' THEN
> pg_replication_origin_progress(CONCAT('pg_', r.srsubid, '_', r.srrelid), false)
> +                           WHEN r.srsubstate IN ('s', 'r') THEN r.srsublsn
> END) AS remote_lsn
> +               FROM pg_subscription_rel r, pg_subscription s
> +               WHERE r.srsubstate IN ('f', 's', 'r') AND s.oid = r.srsubid AND
> s.subfailover
> +           ) UNION (
> +               SELECT pg_replication_origin_progress(CONCAT('pg_',
> s.oid), false) AS remote_lsn
> +               FROM pg_subscription s
> +               WHERE s.subfailover
> +           ));
> 
> What about adding a join to pg_replication_origin to get rid of the "hardcoded"
> format "CONCAT('pg_', r.srsubid, '_', r.srrelid)" and "CONCAT('pg_', s.oid)"?

I tried a bit, but it doesn't seem feasible to get the relationship between
subscription and origin by querying pg_subscription and
pg_replication_origin.

Best Regards,
Hou zj

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).