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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: Peter Smith <smithpb2250@gmail.com>
Cc: Amit Kapila <amit.kapila16@gmail.com>, "houzj.fnst@fujitsu.com" <houzj.fnst@fujitsu.com>, shveta malik <shveta.malik@gmail.com>, "wangw.fnst@fujitsu.com" <wangw.fnst@fujitsu.com>, "shiy.fnst@fujitsu.com" <shiy.fnst@fujitsu.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Dilip Kumar <dilipbalaut@gmail.com>
Date: 2023-02-14T14:14:51Z
Lists: pgsql-hackers 
On Tue, Feb 14, 2023 at 3:58 PM Peter Smith <smithpb2250@gmail.com> wrote:
>
> On Tue, Feb 14, 2023 at 5:04 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
> >
> > On Fri, Feb 10, 2023 at 8:56 AM Peter Smith <smithpb2250@gmail.com> wrote:
> > >
> > > On Fri, Feb 10, 2023 at 1:32 PM houzj.fnst@fujitsu.com
> > > <houzj.fnst@fujitsu.com> wrote:
> > > >
> > > > On Tuesday, February 7, 2023 11:17 AM Amit Kapila <amit.kapila16@gmail.com> wrote:
> > > > >
> > > > > On Mon, Feb 6, 2023 at 3:43 PM houzj.fnst@fujitsu.com
> > > > > <houzj.fnst@fujitsu.com> wrote:
> > > > > >
> > > > > > while reading the code, I noticed that in pa_send_data() we set wait
> > > > > > event to WAIT_EVENT_LOGICAL_PARALLEL_APPLY_STATE_CHANGE while
> > > > > sending
> > > > > > the message to the queue. Because this state is used in multiple
> > > > > > places, user might not be able to distinguish what they are waiting
> > > > > > for. So It seems we'd better to use WAIT_EVENT_MQ_SEND here which will
> > > > > > be eaier to distinguish and understand. Here is a tiny patch for that.
> > > > > >
> > > >
> > > > As discussed[1], we'd better invent a new state for this purpose, so here is the patch
> > > > that does the same.
> > > >
> > > > [1] https://www.postgresql.org/message-id/CAA4eK1LTud4FLRbS0QqdZ-pjSxwfFLHC1Dx%3D6Q7nyROCvvPSfw%40mail.gmail.com
> > > >
> > >
> > > My first impression was the
> > > WAIT_EVENT_LOGICAL_PARALLEL_APPLY_SEND_DATA name seemed misleading
> > > because that makes it sound like the parallel apply worker is doing
> > > the sending, but IIUC it's really the opposite.
> > >
> >
> > So, how about WAIT_EVENT_LOGICAL_APPLY_SEND_DATA?
> >
>
> Yes, IIUC all the LR events are named WAIT_EVENT_LOGICAL_xxx.
>
> So names like the below seem correct format:
>
> a) WAIT_EVENT_LOGICAL_APPLY_SEND_DATA
> b) WAIT_EVENT_LOGICAL_LEADER_SEND_DATA
> c) WAIT_EVENT_LOGICAL_LEADER_APPLY_SEND_DATA

Personally I'm fine even without "LEADER" in the wait event name since
we don't have "who is waiting" in it. IIUC a row of pg_stat_activity
shows who, and the wait event name shows "what the process is
waiting". So I prefer (a).

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.