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: 2021-03-01T10:10:43Z
Lists: pgsql-hackers 
On Fri, Feb 26, 2021 at 4:28 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
>
> On Fri, Feb 26, 2021 at 9:56 AM Amit Kapila <amit.kapila16@gmail.com> wrote:
> >
> > On Thu, Feb 25, 2021 at 12:32 PM Peter Smith <smithpb2250@gmail.com> wrote:
> > >
> >
> > 5. You need to write/sync the spool file at prepare time because after
> > restart between prepare and commit prepared the changes can be lost
> > and won't be resent by the publisher assuming there are commits of
> > other transactions between prepare and commit prepared. For the same
> > reason, I am not sure if we can just rely on the in-memory hash table
> > for it (prepare_spoolfile_exists). Sure, if it exists and there is no
> > restart then it would be cheap to check in the hash table but I don't
> > think it is guaranteed.
> >
>
> As we can't rely on the hash table, I think we can get rid of it and
> always check if the corresponding file exists.
>

Few more related points:
====================
1. Currently, the patch will always clean up the files if there is an
error because SharedFileSetInit registers the cleanup function.
However, we want the files to be removed only if any error happens
before flushing prepare. Once prepare is flushed, we expect the file
will be cleaned up by commit prepared. So, we need to probably call
SharedFileSetUnregister after prepare has been flushed to file.

2. The other point is that I think we need to drop these files (if
any) on Drop Subscription. Investigate if any variant of Alter needs
similar handling.

-- 
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