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

On Tuesday, January 10, 2023 7:48 PM Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote:
>
> On Tue, Jan 10, 2023 at 10:26 AM houzj(dot)fnst(at)fujitsu(dot)com
> <houzj(dot)fnst(at)fujitsu(dot)com> wrote:
> >
> > On Monday, January 9, 2023 4:51 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>
> wrote:
> > >
> > > On Sun, Jan 8, 2023 at 11:32 AM houzj(dot)fnst(at)fujitsu(dot)com
> > > <houzj(dot)fnst(at)fujitsu(dot)com> wrote:
> > > >
> > > > On Sunday, January 8, 2023 11:59 AM houzj(dot)fnst(at)fujitsu(dot)com
> > > <houzj(dot)fnst(at)fujitsu(dot)com> wrote:
> > > > > Attach the updated patch set.
> > > >
> > > > Sorry, the commit message of 0001 was accidentally deleted, just
> > > > attach the same patch set again with commit message.
> > > >
> > >
> > > Pushed the first (0001) patch.
> >
> > Thanks for pushing, here are the remaining patches.
> > I reordered the patch number to put patches that are easier to commit
> > in the front of others.
>
> I was looking into 0001, IMHO the pid should continue to represent the main
> apply worker. So the pid will always show the main apply worker which is
> actually receiving all the changes for the subscription (in short working as
> logical receiver) and if it is applying changes through a parallel worker then it
> should put the parallel worker pid in a new column called 'parallel_worker_pid'
> or 'parallel_apply_worker_pid' otherwise NULL. Thoughts?

Thanks for the comment.

IIRC, you mean something like following, right ?
(sorry if I misunderstood)
--
For parallel apply worker:
'pid' column shows the pid of the leader, new column parallel_worker_pid shows its own pid

For leader apply worker:
'pid' column shows its own pid, new column parallel_worker_pid shows 0
--

If so, I am not sure if the above is better, because it is changing the
existing column's('pid') meaning, the 'pid' will no longer represent the pid of
the worker itself. Besides, it seems not consistent with what we have for
parallel query workers in pg_stat_activity. What do you think ?

Best regards,
Hou zj