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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: "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.com>, Alexander Lakhin <exclusion@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2023-05-09T02:19:47Z
Lists: pgsql-hackers 
On Mon, May 8, 2023 at 8:09 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
>
> On Fri, May 5, 2023 at 9:14 AM Zhijie Hou (Fujitsu)
> <houzj.fnst@fujitsu.com> wrote:
> >
> > On Wednesday, May 3, 2023 3:17 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
> > >
> >
> > Attach another patch to fix the problem that pa_shutdown will access invalid
> > MyLogicalRepWorker. I personally want to avoid introducing new static variable,
> > so I only reorder the callback registration in this version.
> >
> > When testing this, I notice a rare case that the leader is possible to receive
> > the worker termination message after the leader stops the parallel worker. This
> > is unnecessary and have a risk that the leader would try to access the detached
> > memory queue. This is more likely to happen and sometimes cause the failure in
> > regression tests after the registration reorder patch because the dsm is
> > detached earlier after applying the patch.
> >
>
> I think it is only possible for the leader apply can worker to try to
> receive the error message from an error queue after your 0002 patch.
> Because another place already detached from the queue before stopping
> the parallel apply workers. So, I combined both the patches and
> changed a few comments and a commit message. Let me know what you
> think of the attached.

I have one comment on the detaching error queue part:

+       /*
+        * Detach from the error_mq_handle for the parallel apply worker before
+        * stopping it. This prevents the leader apply worker from trying to
+        * receive the message from the error queue that might already
be detached
+        * by the parallel apply worker.
+        */
+       shm_mq_detach(winfo->error_mq_handle);
+       winfo->error_mq_handle = NULL;

In pa_detach_all_error_mq(), we try to detach error queues of all
workers in the pool. I think we should check if the queue is already
detached (i.e. is NULL) there. Otherwise, we will end up a SEGV if an
error happens after detaching the error queue and before removing the
worker from the pool.

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.