Horton

Re: Synchronizing slots from primary to standby

shveta malik <shveta.malik@gmail.com>

View thread View on postgr.es
From: shveta malik <shveta.malik@gmail.com>
To: "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.com>
Cc: Amit Kapila <amit.kapila16@gmail.com>, Bertrand Drouvot <bertranddrouvot.pg@gmail.com>, Ajin Cherian <itsajin@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>, shveta malik <shveta.malik@gmail.com>
Date: 2024-03-29T04:02:41Z
Lists: pgsql-hackers

Attachments

On Fri, Mar 29, 2024 at 6:36 AM Zhijie Hou (Fujitsu)
<houzj.fnst@fujitsu.com> wrote:
>
> Attach a new version patch which fixed an un-initialized variable issue and
> added some comments. Also, temporarily enable DEBUG2 for the 040 tap-test so that
> we can analyze the possible CFbot failures easily.

As suggested by Amit in [1], for the fix being discussed where we need
to advance the synced slot on standby, we need to skip the dbid check
in fast_forward mode in CreateDecodingContext(). We tried few tests to
make sure that there was no table-access done during fast-forward mode

1) Initially we tried avoiding database-id check in
CreateDecodingContext() only when called by
pg_logical_replication_slot_advance(). 'make check-world' passed on
HEAD for the same.

2) But the more generic solution was to skip the database check if
"fast_forward" is true. It was tried and 'make check-world' passed on
HEAD for that as well.

3) Another thing tried by Hou-San was to run pgbench after skipping db
check in the fast_forward logical decoding case.
pgbench was run to generate some changes and then the logical slot was
advanced to the latest position in another database. A LOG was added
in relation_open to catch table access. It was found that there was no
table-access in fast forward logical decoding i.e. no LOGS for
table-open were generated during the test. Steps given at [2]

[1]: https://www.postgresql.org/message-id/CAA4eK1KMiKangJa4NH_K1oFc87Y01n3rnpuwYagT59Y%3DADW8Dw%40mail.gmail.com

[2]:
--------------
1. apply the DEBUG patch (attached as .txt) which will log the
relation open and table cache access.

2. create a slot:
SELECT 'init' FROM pg_create_logical_replication_slot('logicalslot',
'test_decoding', false, false, true);

3. run pgbench to generate some data.
pgbench -i postgres
pgbench --aggregate-interval=5 --time=5 --client=10 --log --rate=1000
--latency-limit=10 --failures-detailed --max-tries=10 postgres

4. start a fresh session in a different db and advance the slot to the
latest position. There should be no relation open or CatCache log
between the LOG "starting logical decoding for slot .." and LOG
"decoding over".
SELECT pg_replication_slot_advance('logicalslot', pg_current_wal_lsn());
--------------

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).