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: vignesh C <vignesh21@gmail.com>, PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Date: 2021-03-09T09:41:42Z
Lists: pgsql-hackers 
On Tue, Mar 9, 2021 at 3:02 PM Peter Smith <smithpb2250@gmail.com> wrote:
>
> On Mon, Mar 8, 2021 at 4:58 PM vignesh C <vignesh21@gmail.com> wrote:
> >
> > +               while (AnyTablesyncInProgress())
> > +               {
> > +                       process_syncing_tables(begin_data.final_lsn);
> > +
> > +                       /* This latch is to prevent 100% CPU looping. */
> > +                       (void) WaitLatch(MyLatch,
> > +                                                        WL_LATCH_SET
> > | WL_TIMEOUT | WL_EXIT_ON_PM_DEATH,
> > +                                                        1000L,
> > WAIT_EVENT_LOGICAL_SYNC_STATE_CHANGE);
> > +                       ResetLatch(MyLatch);
> > +               }
> > Should we have CHECK_FOR_INTERRUPTS inside the while loop?
>
> The process_syncing_tables will end up in the
> process_syncing_tables_for_apply() function. And in that function IIUC
> the apply worker is spending most of the time waiting for the
> tablesync to achieve SYNCDONE state.
> See wait_for_relation_state_change(rstate->relid, SUBREL_STATE_SYNCDONE);
>

But, I think for large copy, it won't wait in that state because the
tablesync worker will still be in SUBREL_STATE_DATASYNC state and we
wait for SUBREL_STATE_SYNCDONE state only after the initial copy is
finished. So, I think it is a good idea to call CHECK_FOR_INTERRUPTS
in this loop.

-- 
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