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

Zhijie Hou (Fujitsu) <houzj.fnst@fujitsu.com>

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From: "houzj.fnst@fujitsu.com" <houzj.fnst@fujitsu.com>
To: Amit Kapila <amit.kapila16@gmail.com>
Cc: Masahiko Sawada <sawada.mshk@gmail.com>, "wangw.fnst@fujitsu.com" <wangw.fnst@fujitsu.com>, Dilip Kumar <dilipbalaut@gmail.com>, "shiy.fnst@fujitsu.com" <shiy.fnst@fujitsu.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Peter Smith <smithpb2250@gmail.com>
Date: 2022-12-13T13:07:06Z
Lists: pgsql-hackers

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On Tuesday, December 13, 2022 6:41 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
> 
> On Tue, Dec 13, 2022 at 4:36 AM Peter Smith <smithpb2250@gmail.com>
> wrote:
> >
> > ~~~
> >
> > 3. pa_set_stream_apply_worker
> >
> > +/*
> > + * Set the worker that required to apply the current streaming transaction.
> > + */
> > +void
> > +pa_set_stream_apply_worker(ParallelApplyWorkerInfo *winfo) {
> > +stream_apply_worker = winfo; }
> >
> > Comment wording seems wrong.
> >
> 
> I think something like "Cache the parallel apply worker information."
> may be more suitable here.

Changed.

> Few more similar cosmetic comments:
> 1.
> + /*
> + * Unlock the shared object lock so that the parallel apply worker
> + * can continue to receive changes.
> + */
> + if (!first_segment)
> + pa_unlock_stream(winfo->shared->xid, AccessExclusiveLock);
> 
> This comment is missing in the new (0002) patch.

Added.

> 2.
> + if (!winfo->serialize_changes)
> + {
> + if (!first_segment)
> + pa_unlock_stream(winfo->shared->xid, AccessExclusiveLock);
> 
> I think we should write some comments on why we are not unlocking when
> serializing changes.

Added.

> 3. Please add a comment like below in the patch to make it clear why in
> stream_abort case we perform locking before sending the message.
> --- a/src/backend/replication/logical/worker.c
> +++ b/src/backend/replication/logical/worker.c
> @@ -1858,6 +1858,13 @@ apply_handle_stream_abort(StringInfo s)
>                          * worker will wait on the lock for the next set of
> changes after
>                          * processing the STREAM_ABORT message if it is not
> already waiting
>                          * for STREAM_STOP message.
> +                        *
> +                        * It is important to perform this locking
> before sending the
> +                        * STREAM_ABORT message so that the leader can
> hold the lock first
> +                        * and the parallel apply worker will wait for
> the leader to release
> +                        * the lock. This is the same as what we do in
> +                        * apply_handle_stream_stop. See Locking
> Considerations atop
> +                        * applyparallelworker.c.
>                          */
>                         if (!toplevel_xact)

Merged.

Attach the new version patch which addressed above comments.
I also slightly refactored logic related to pa_spooled_messages() so that
It doesn't need to wait for a timeout if there are pending spooled messages.

Best regards,
Hou zj

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.