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: 2021-02-27T03:17:54Z
Lists: pgsql-hackers 
On Sat, Feb 27, 2021 at 7:31 AM Peter Smith <smithpb2250@gmail.com> wrote:
>
> On Fri, Feb 26, 2021 at 9:58 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
> > 6.
> > + * XXX - Is there a potential timing problem here - e.g. if signal arrives
> > + * while executing this then maybe we will set table_states_valid without
> > + * refetching them?
> > + */
> > +static void
> > +FetchTableStates(bool *started_tx)
> > ..
> >
> > Can you explain which race condition you are worried about here which
> > is not possible earlier but can happen after this patch?
> >
>
> Yes, my question (in that XXX comment) was not about anything new for
> the current patch, because this FetchTableStates function has exactly
> the same logic as the HEAD code.
>
> I was only wondering if there is any possibility that one of the
> function calls (inside the if block) can end up calling
> CHECK_INTERRUPTS. If that could happen, then perhaps the
> table_states_valid  flag could be assigned false (by the
> invalidate_syncing_table_states signal handler) only to be
> immediately/wrongly overwritten as table_states_valid  = true in this
> FetchTableStates code.
>

This is not related to CHECK_FOR_INTERRUPTS. The
invalidate_syncing_table_states() can be called only when we process
invalidation messages which we do while locking the relation via
GetSubscriptionRelationstable_open->relation_open->LockRelationOid.
After that, it won't be done in that part of the code. So, I think we
don't need this comment.

-- 
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