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

On Fri, Aug 19, 2022 at 7:55 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>
> On Fri, Aug 19, 2022 at 3:05 PM Peter Smith <smithpb2250(at)gmail(dot)com> wrote:
> >
> > 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 think it is only to distinguish between leader apply worker and
> background apply workers. The tablesync worker can be distinguished
> based on relid field.
>

Right. But that's the reason for my question in the first place - why
implement the patch so that the user still has to jump through hoops
just to know the worker type information?

e.g.

Option 1 (patch) - if there is a non-NULL relid field then the worker
type must be a tablesyc worker, otherwise if there is non-NULL a
leader_pid field then the worker type must be an apply background
worker, otherwise the worker type must be an apply main worker.

versus

Option 2 - new worker_type field (values 't','p','a')

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