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

On Tue, Jan 17, 2023 at 6:14 PM houzj(dot)fnst(at)fujitsu(dot)com
<houzj(dot)fnst(at)fujitsu(dot)com> wrote:
>
> On Tuesday, January 17, 2023 2:46 PM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
> >
> > On Tue, Jan 17, 2023 at 12:37 PM houzj(dot)fnst(at)fujitsu(dot)com
> > <houzj(dot)fnst(at)fujitsu(dot)com> wrote:
> > > Attach the new version 0001 patch which addressed all other comments.
> > >
> >
> > Thank you for updating the patch. Here is one comment:
> >
> > @@ -426,14 +427,24 @@ pg_stat_get_activity(PG_FUNCTION_ARGS)
> >
> > /*
> > * Show the leader only for active parallel
> > workers. This
> > - * leaves the field as NULL for the
> > leader of a parallel
> > - * group.
> > + * leaves the field as NULL for the
> > leader of a parallel group
> > + * or the leader of parallel apply workers.
> > */
> > if (leader && leader->pid !=
> > beentry->st_procpid)
> > {
> > values[28] =
> > Int32GetDatum(leader->pid);
> > nulls[28] = false;
> > }
> > + else
> > + {
> > + int
> > leader_pid = GetLeaderApplyWorkerPid(beentry->st_procpid);
> > +
> > + if (leader_pid != InvalidPid)
> > + {
> > + values[28] =
> > Int32GetDatum(leader_pid);
> > + nulls[28] = false;
> > + }
> > + }
> > }
> >
> > I'm slightly concerned that there could be overhead of executing
> > GetLeaderApplyWorkerPid () for every backend process except for parallel
> > query workers. The number of such backends could be large and
> > GetLeaderApplyWorkerPid() acquires the lwlock. For example, does it make
> > sense to check (st_backendType == B_BG_WORKER) before calling
> > GetLeaderApplyWorkerPid()? Or it might not be a problem since it's
> > LogicalRepWorkerLock which is not likely to be contended.
>
> Thanks for the comment and I think your suggestion makes sense.
> I have added the check before getting the leader pid. Here is the new version patch.

Thank you for updating the patch. Looks good to me.

Regards,

--
Masahiko Sawada
Amazon Web Services: https://aws.amazon.com