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

Dilip Kumar <dilipbalaut@gmail.com>

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From: Dilip Kumar <dilipbalaut@gmail.com>
To: "houzj.fnst@fujitsu.com" <houzj.fnst@fujitsu.com>
Cc: Amit Kapila <amit.kapila16@gmail.com>, Masahiko Sawada <sawada.mshk@gmail.com>, "wangw.fnst@fujitsu.com" <wangw.fnst@fujitsu.com>, Peter Smith <smithpb2250@gmail.com>, "shiy.fnst@fujitsu.com" <shiy.fnst@fujitsu.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2023-01-11T06:03:50Z
Lists: pgsql-hackers 
On Wed, Jan 11, 2023 at 9:34 AM houzj.fnst@fujitsu.com
<houzj.fnst@fujitsu.com> wrote:
>

> > I was looking into 0001, IMHO the pid should continue to represent the main
> > apply worker. So the pid will always show the main apply worker which is
> > actually receiving all the changes for the subscription (in short working as
> > logical receiver) and if it is applying changes through a parallel worker then it
> > should put the parallel worker pid in a new column called 'parallel_worker_pid'
> > or 'parallel_apply_worker_pid' otherwise NULL.  Thoughts?
>
> Thanks for the comment.
>
> IIRC, you mean something like following, right ?
> (sorry if I misunderstood)
> --
> For parallel apply worker:
> 'pid' column shows the pid of the leader, new column parallel_worker_pid shows its own pid
>
> For leader apply worker:
> 'pid' column shows its own pid, new column parallel_worker_pid shows 0
> --
>
> If so, I am not sure if the above is better, because it is changing the
> existing column's('pid') meaning, the 'pid' will no longer represent the pid of
> the worker itself. Besides, it seems not consistent with what we have for
> parallel query workers in pg_stat_activity. What do you think ?

Actually, I always imagined the pid is the process id of the worker
which is actually receiving the changes for the subscriber. Keeping
the pid to represent the leader makes more sense.  But as you said,
that parallel worker for backend is already following the terminology
as you have in your patch to show the pid as the pid of the applying
worker so I am fine with the way you have.

-- 
Regards,
Dilip Kumar
EnterpriseDB: http://www.enterprisedb.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.