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Re: Perform streaming logical transactions by background workers and parallel apply

Amit Kapila <amit.kapila16@gmail.com>

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From: Amit Kapila <amit.kapila16@gmail.com>
To: Masahiko Sawada <sawada.mshk@gmail.com>
Cc: "houzj.fnst@fujitsu.com" <houzj.fnst@fujitsu.com>, "wangw.fnst@fujitsu.com" <wangw.fnst@fujitsu.com>, Peter Smith <smithpb2250@gmail.com>, Dilip Kumar <dilipbalaut@gmail.com>, "shiy.fnst@fujitsu.com" <shiy.fnst@fujitsu.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2022-12-07T07:31:34Z
Lists: pgsql-hackers 
On Wed, Dec 7, 2022 at 10:10 AM Masahiko Sawada <sawada.mshk@gmail.com> wrote:
>
> On Wed, Dec 7, 2022 at 1:29 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
> >
> > Right, but the leader will anyway exit at some point either due to an
> > ERROR like "lost connection ... to parallel worker" or with a LOG
> > like: "... will restart because of a parameter change" but I see your
> > point. So, will it be better if we have a LOG message here and then
> > proc_exit()? Do you have something else in mind for this?
>
> No, I was thinking that too. It's better to write a LOG message and do
> proc_exit().
>
> Regarding the error "lost connection ... to parallel worker", it could
> still happen depending on the timing even if the parallel worker
> cleanly exits due to parameter changes, right? If so, I'm concerned
> that it could lead to disable the subscription unexpectedly if
> disable_on_error is enabled.
>

If we want to avoid this then I think we have the following options
(a) parallel apply skips checking parameter change (b) parallel worker
won't exit on parameter change but will silently absorb the parameter
and continue its processing; anyway, the leader will detect it and
stop the worker for the parameter change

Among these, the advantage of (b) is that it will allow reflecting the
parameter change (that doesn't need restart) in the parallel worker.
Do you have any better idea to deal with this?

-- 
With Regards,
Amit Kapila.

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Fix invalid memory access during the shutdown of the parallel apply worker.

  2. Fix assertion failure in apply worker.

  3. Use elog to report unexpected action in handle_streamed_transaction().

  4. Use appropriate wait event when sending data in the apply worker.

  5. Allow the logical_replication_mode to be used on the subscriber.

  6. Rename GUC logical_decoding_mode to logical_replication_mode.

  7. Display the leader apply worker's PID for parallel apply workers.

  8. Improve the code to decide and process the apply action.

  9. Document the newly added wait events added by commit 216a784829.

  10. Perform apply of large transactions by parallel workers.

  11. Wake up a subscription's replication worker processes after DDL.

  12. Add copyright notices to meson files

  13. Better document logical replication parameters

  14. Add a common function to generate the origin name.

  15. Harmonize parameter names in storage and AM code.

  16. Avoid using list_length() to test for empty list.

  17. Improve two comments related to a boolean DefElem's value

  18. Fix partition table's REPLICA IDENTITY checking on the subscriber.

  19. Fix data inconsistency between publisher and subscriber.

  20. Fix cache look-up failures while applying changes in logical replication.