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

On Wednesday, December 7, 2022 7:51 PM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
>
> On Mon, Dec 5, 2022 at 1:29 PM houzj(dot)fnst(at)fujitsu(dot)com
> <houzj(dot)fnst(at)fujitsu(dot)com> wrote:
> >
> > On Sunday, December 4, 2022 7:17 PM houzj(dot)fnst(at)fujitsu(dot)com
> <houzj(dot)fnst(at)fujitsu(dot)com>
> > >
> > > Thursday, December 1, 2022 8:40 PM Amit Kapila
> <amit(dot)kapila16(at)gmail(dot)com>
> > > wrote:
> > > > Some other comments:
> > > ...
> > > Attach the new version patch set which addressed most of the comments
> > > received so far except some comments being discussed[1].
> > > [1]
> https://www.postgresql.org/message-id/OS0PR01MB57167BF64FC0891734C
> 8E81A94149%40OS0PR01MB5716.jpnprd01.prod.outlook.com
> >
> > Attach a new version patch set which fixed a testcase failure on CFbot.
>
> ---
> If a value of max_parallel_apply_workers_per_subscription is not
> sufficient, we get the LOG "out of parallel apply workers" every time
> when the apply worker doesn't launch a worker. But do we really need
> this log? It seems not consistent with
> max_sync_workers_per_subscription behavior. I think we can check if
> the number of running parallel workers is less than
> max_parallel_apply_workers_per_subscription before calling
> logicalrep_worker_launch(). What do you think?

(Sorry, I missed this comment in last email)

I personally feel giving a hint might help user to realize that the
max_parallel_applyxxx is not enough for the current workload and then they can
adjust the parameter. Otherwise, user might have an easy way to check if more
workers are needed.

Best regards,
Hou zj