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

On Thu, Jan 12, 2023 at 10:34 AM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>
> On Thu, Jan 12, 2023 at 9:54 AM Peter Smith <smithpb2250(at)gmail(dot)com> wrote:
> >
> >
> > doc/src/sgml/monitoring.sgml
> >
> > 5. pg_stat_subscription
> >
> > @@ -3198,11 +3198,22 @@ SELECT pid, wait_event_type, wait_event FROM
> > pg_stat_activity WHERE wait_event i
> >
> > <row>
> > <entry role="catalog_table_entry"><para role="column_definition">
> > + <structfield>apply_leader_pid</structfield> <type>integer</type>
> > + </para>
> > + <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.
> > + </para></entry>
> > + </row>
> > +
> > + <row>
> > + <entry role="catalog_table_entry"><para role="column_definition">
> > <structfield>relid</structfield> <type>oid</type>
> > </para>
> > <para>
> > OID of the relation that the worker is synchronizing; null for the
> > - main apply worker
> > + main apply worker and the parallel apply worker
> > </para></entry>
> > </row>
> >
> > 5a.
> >
> > (Same as general comment #1 about terminology)
> >
> > "apply_leader_pid" --> "leader_apply_pid"
> >
>
> How about naming this as just leader_pid? I think it could be helpful
> in the future if we decide to parallelize initial sync (aka parallel
> copy) because then we could use this for the leader PID of parallel
> sync workers as well.
>
> --

I still prefer leader_apply_pid.
leader_pid does not tell which 'operation' it belongs to. 'apply'
gives the clarity that it is apply related process.

The terms used in patch look very confusing. I had to read a few lines
multiple times to understand it.

1.
Summary says 'main_worker_pid' to be added but I do not see
'main_worker_pid' added in pg_stat_subscription, instead I see
'apply_leader_pid'. Am I missing something? Also, as stated above
'leader_apply_pid' makes more sense.
it is better to correct it everywhere (apply leader-->leader apply).
Once that is done, it can be reviewed again.

thanks
Shveta