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

On Tues, Sep 13, 2022 at 17:49 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>

Thanks for your comments.

> On Fri, Sep 9, 2022 at 2:31 PM houzj(dot)fnst(at)fujitsu(dot)com
> <houzj(dot)fnst(at)fujitsu(dot)com> wrote:
> >
> > On Friday, September 9, 2022 3:02 PM Peter Smith <smithpb2250(at)gmail(dot)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