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

Wei Wang (Fujitsu) <wangw.fnst@fujitsu.com>

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From: "wangw.fnst@fujitsu.com" <wangw.fnst@fujitsu.com>
To: Amit Kapila <amit.kapila16@gmail.com>, "houzj.fnst@fujitsu.com" <houzj.fnst@fujitsu.com>
Cc: Peter Smith <smithpb2250@gmail.com>, Dilip Kumar <dilipbalaut@gmail.com>, Masahiko Sawada <sawada.mshk@gmail.com>, "shiy.fnst@fujitsu.com" <shiy.fnst@fujitsu.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2022-09-15T05:20:54Z
Lists: pgsql-hackers 
On Tues, Sep 13, 2022 at 17:49 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
>

Thanks for your comments.

> On Fri, Sep 9, 2022 at 2:31 PM houzj.fnst@fujitsu.com
> <houzj.fnst@fujitsu.com> wrote:
> >
> > On Friday, September 9, 2022 3:02 PM Peter Smith <smithpb2250@gmail.com>
> wrote:
> > >
> >
> > > 3.
> > >
> > > max_logical_replication_workers (integer)
> > >     Specifies maximum number of logical replication workers. This
> > > includes apply leader workers, parallel apply workers, and table
> > > synchronization workers.
> > >     Logical replication workers are taken from the pool defined by
> > > max_worker_processes.
> > >     The default value is 4. This parameter can only be set at server start.
> > >
> > > ~
> > >
> > > I did not really understand why the default is 4. Because the  default
> > > tablesync workers is 2, and the default parallel workers is 2, but
> > > what about accounting for the apply worker? Therefore, shouldn't
> > > max_logical_replication_workers default be 5 instead of 4?
> >
> > The parallel apply is disabled by default, so it's not a must to increase this
> > global default value as discussed[1]
> >
> > [1] https://www.postgresql.org/message-
> id/CAD21AoCwaU8SqjmC7UkKWNjDg3Uz4FDGurMpis3zw5SEC%2B27jQ%40mail
> .gmail.com
> >
> 
> Okay, but can we document to increase this value when the parallel
> apply is enabled?

Add the following sentence in the chapter [31.10. Configuration Settings]:
```
In addition, if the subscription parameter <literal>streaming</literal> is set
to <literal>parallel</literal>, please increase
<literal>max_logical_replication_workers</literal> according to the desired
number of parallel apply workers.
```

The new patches were attached in [1].

[1] - https://www.postgresql.org/message-id/OS3PR01MB6275F145878B4A44586C46CE9E499%40OS3PR01MB6275.jpnprd01.prod.outlook.com

Regards,
Wang wei

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.