Horton

Re: Skipping logical replication transactions on subscriber side

Masahiko Sawada <sawada.mshk@gmail.com>

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From: Masahiko Sawada <sawada.mshk@gmail.com>
To: Amit Kapila <amit.kapila16@gmail.com>
Cc: Peter Eisentraut <peter.eisentraut@enterprisedb.com>, "houzj.fnst@fujitsu.com" <houzj.fnst@fujitsu.com>, vignesh C <vignesh21@gmail.com>, Greg Nancarrow <gregn4422@gmail.com>, "tanghy.fnst@fujitsu.com" <tanghy.fnst@fujitsu.com>, "osumi.takamichi@fujitsu.com" <osumi.takamichi@fujitsu.com>, Alexey Lesovsky <lesovsky@gmail.com>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2021-12-08T11:22:32Z
Lists: pgsql-hackers 
On Wed, Dec 8, 2021 at 4:05 PM Masahiko Sawada <sawada.mshk@gmail.com> wrote:
> > Okay, I understand those cases but note always checking if the
> > prepared xact exists during commit prepared has a cost and that is why
> > we avoided it at the first place.

BTW what costs were we concerned about? Looking at LookupGXact(), we
look for the 2PC state data on shmem while acquiring TwoPhaseStateLock
in shared mode. And we check origin_lsn and origin_timestamp of 2PC by
reading WAL or 2PC state file only if gid matched. On the other hand,
committing the prepared transaction does WAL logging, waits for
synchronous replication, and calls post-commit callbacks, and removes
2PC state file etc. And it requires acquiring TwoPhaseStateLock in
exclusive mode to remove 2PC state entry. So it looks like always
checking if the prepared transaction exists and skipping it if not is
cheaper than always committing prepared transactions.

Regards,

-- 
Masahiko Sawada
EDB:  https://www.enterprisedb.com/

Commits

  1. Test ALIGNOF_DOUBLE==4 compatibility under ALIGNOF_DOUBLE==8.

  2. Reorder subskiplsn in pg_subscription to avoid alignment issues.

  3. Add ALTER SUBSCRIPTION ... SKIP.

  4. Optionally disable subscriptions on error.

  5. Update docs of logical replication for commit 8d74fc96db.

  6. Respect permissions within logical replication.

  7. Fix regression test failure caused by commit 8d74fc96db.

  8. Add a view to show the stats of subscription workers.

  9. Add logical change details to logical replication worker errcontext.

  10. Rename LOGICAL_REP_MSG_STREAM_END to LOGICAL_REP_MSG_STREAM_STOP.

  11. Fix typo in protocol.sgml.

  12. Remove unused argument in apply_handle_commit_internal().

  13. Fix replication of in-progress transactions in tablesync worker.

  14. Reorder pg_sequence columns to avoid alignment issue