Horton

Re: [HACKERS] logical decoding of two-phase transactions

Amit Kapila <amit.kapila16@gmail.com>

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From: Amit Kapila <amit.kapila16@gmail.com>
To: Peter Smith <smithpb2250@gmail.com>
Cc: Ajin Cherian <itsajin@gmail.com>, PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Date: 2020-11-25T09:18:24Z
Lists: pgsql-hackers 
On Wed, Nov 25, 2020 at 12:54 PM Peter Smith <smithpb2250@gmail.com> wrote:
>
> Hi Amit.
>
> IIUC the tablesync worker runs in a single transaction.
>
> Last week I discovered and described [1] a problem where/if (by
> unlucky timing) the tablesync worker gets to handle the 2PC PREPARE
> TRANSACTION then that whole single tx is getting committed, regardless
> that a COMMIT PREPARED was not even been executed yet. i.e. It means
> if the publisher subsequently does a ROLLBACK PREPARED then the table
> records on Pub/Sub nodes will no longer be matching.
>
> AFAIK this is a new problem for the current WIP patch because prior to
> this the PREPARE had no decoding.
>
> Please let me know if this issue description is still not clear.
>
> Did you have any thoughts how we might address this issue?
>

I think we need to disable two_phase_commit for table sync workers. We
anyway wanted to expose a parater via subscription for that and we can
use that to do it. Also, there were some other comments [1] related to
tablesync worker w.r.t prepared transactions which would possibly be
addressed by doing it. Kindly check those comments [1] and let me know
if anything additional is required.

[1] - https://www.postgresql.org/message-id/87zhxrwgvh.fsf%40ars-thinkpad

-- 
With Regards,
Amit Kapila.

Commits

  1. Add prepare API support for streaming transactions in logical replication.

  2. Doc: minor improvements for logical replication protocol documentation.

  3. Fix test failure in 021_twophase.pl.

  4. Refactor to make common functions in proto.c and worker.c.

  5. Unify PostgresNode's new() and get_new_node() methods

  6. Fix potential buffer overruns in proto.c.

  7. Add support for prepared transactions to built-in logical replication.

  8. Refactor function parse_subscription_options.

  9. Allow enabling two-phase option via replication protocol.

  10. Don't use Asserts to check for violations of replication protocol.

  11. Improve psql tab completion for options of subcriptions and publications

  12. Rearrange logrep worker's snapshot handling some more.

  13. doc: Update information of new messages for logical replication.

  14. ALTER SUBSCRIPTION ... ADD/DROP PUBLICATION

  15. Allow pgoutput to send logical decoding messages.

  16. Refactor function parse_output_parameters.

  17. Avoid repeated decoding of prepared transactions after a restart.

  18. Fix an oversight in ReorderBufferFinishPrepared.

  19. Allow multiple xacts during table sync in logical replication.

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

  21. Fix 'skip-empty-xacts' option in test_decoding for streaming mode.

  22. Use Enum for top level logical replication message types.

  23. Add support for streaming to built-in logical replication.

  24. Fix the logical streaming test.

  25. Implement streaming mode in ReorderBuffer.

  26. Extend the logical decoding output plugin API with stream methods.

  27. Store 2PC GID in commit/abort WAL recs for logical decoding