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

Masahiko Sawada <sawada.mshk@gmail.com>

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From: Masahiko Sawada <sawada.mshk@gmail.com>
To: Amit Kapila <amit.kapila16@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: 2022-12-08T07:10:22Z
Lists: pgsql-hackers 
On Thu, Dec 8, 2022 at 1:52 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
>
> On Wed, Dec 7, 2022 at 6:33 PM houzj.fnst@fujitsu.com
> <houzj.fnst@fujitsu.com> wrote:
> >
> > On Wednesday, December 7, 2022 7:51 PM Masahiko Sawada <sawada.mshk@gmail.com> wrote:
> > >
> >
> > > ---
> > > When max_parallel_apply_workers_per_subscription is changed to a value
> > > lower than the number of parallel worker running at that time, do we
> > > need to stop extra workers?
> >
> > I think we can do this, like adding a check in the main loop of leader worker, and
> > check every time after reloading the conf. OTOH, we will also stop the worker after
> > finishing a transaction, so I am slightly not sure do we need to add another check logic here.
> > But I am fine to add it if you think it would be better.
> >
>
> I think this is tricky because it is possible that all active workers
> are busy with long-running transactions, so, I think stopping them
> doesn't make sense.

Right, we should not stop running parallel workers.

> I think as long as we are freeing them after use
> it seems okay to me. OTOH, each time after finishing the transaction,
> we can stop the workers, if the workers in the free pool exceed
> 'max_parallel_apply_workers_per_subscription'.

Or the apply leader worker can check that after reloading the config file.

Regards,

-- 
Masahiko Sawada
Amazon Web Services: https://aws.amazon.com

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.