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

On Wed, Jan 11, 2023 at 9:34 AM houzj(dot)fnst(at)fujitsu(dot)com
<houzj(dot)fnst(at)fujitsu(dot)com> wrote:
>
> On Tuesday, January 10, 2023 7:48 PM Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote:
> >
> > 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 existing column's('pid') meaning, the 'pid' will no longer represent the pid of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 ?
>

+1. I think it makes sense to keep it similar to pg_stat_activity.

+ <para>
+ Process ID of the leader apply worker, if this process is a apply
+ parallel worker. NULL if this process is a leader apply worker or a
+ synchronization worker.

Can we change the above description to something like: "Process ID of
the leader apply worker, if this process is a parallel apply worker.
NULL if this process is a leader apply worker or does not participate
in parallel apply, or a synchronization worker."?

--
With Regards,
Amit Kapila.