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

On Fri, Aug 19, 2022 at 7:10 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>
> On Fri, Aug 19, 2022 at 2:36 PM Peter Smith <smithpb2250(at)gmail(dot)com> wrote:
> >
> > Here are my review comments for the v23-0005 patch:
> >
> > ======
> >
> > Commit Message says:
> > main_worker_pid is Process ID of the main apply worker, if this process is a
> > apply background worker. NULL if this process is a main apply worker or a
> > synchronization worker.
> > The new column can make it easier to distinguish main apply worker and apply
> > background worker.
> >
> > --
> >
> > Having a column called ‘main_worker_pid’ which is defined to be NULL
> > if the process *is* the main apply worker does not make any sense to
> > me.
> >
>
> I haven't read this part of a patch but it seems to me we have
> something similar for parallel query workers. Refer 'leader_pid'
> column in pg_stat_activity.
>

IIUC (from the patch 0005 commit message) the intention is to be able
to easily distinguish the worker types.

I thought using a leader PID (by whatever name) seemed a poor way to
achieve that in this case because the PID is either NULL or not NULL,
but there are 3 kinds of subscription workers, not 2.

------
Kind Regards,
Peter Smith.
Fujitsu Australia