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

On Tue, Jan 17, 2023 at 1:21 PM houzj(dot)fnst(at)fujitsu(dot)com
<houzj(dot)fnst(at)fujitsu(dot)com> wrote:
>
> On Tuesday, January 17, 2023 5:43 AM Peter Smith <smithpb2250(at)gmail(dot)com> wrote:
> >
> > On Mon, Jan 16, 2023 at 5:41 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>
> > wrote:
> > >
> > > On Mon, Jan 16, 2023 at 10:24 AM Peter Smith <smithpb2250(at)gmail(dot)com>
> > wrote:
> > > >
> > > > 2.
> > > >
> > > > /*
> > > > + * Return the pid of the leader apply worker if the given pid is
> > > > +the pid of a
> > > > + * parallel apply worker, otherwise return InvalidPid.
> > > > + */
> > > > +pid_t
> > > > +GetLeaderApplyWorkerPid(pid_t pid)
> > > > +{
> > > > + int leader_pid = InvalidPid;
> > > > + int i;
> > > > +
> > > > + LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
> > > > +
> > > > + for (i = 0; i < max_logical_replication_workers; i++) {
> > > > + LogicalRepWorker *w = &LogicalRepCtx->workers[i];
> > > > +
> > > > + if (isParallelApplyWorker(w) && w->proc && pid == w->proc->pid) {
> > > > + leader_pid = w->leader_pid; break; } }
> > > > +
> > > > + LWLockRelease(LogicalRepWorkerLock);
> > > > +
> > > > + return leader_pid;
> > > > +}
> > > >
> > > > 2a.
> > > > IIUC the IsParallelApplyWorker macro does nothing except check that
> > > > the leader_pid is not InvalidPid anyway, so AFAIK this algorithm
> > > > does not benefit from using this macro because we will want to
> > > > return InvalidPid anyway if the given pid matches.
> > > >
> > > > So the inner condition can just say:
> > > >
> > > > if (w->proc && w->proc->pid == pid)
> > > > {
> > > > leader_pid = w->leader_pid;
> > > > break;
> > > > }
> > > >
> > >
> > > Yeah, this should also work but I feel the current one is explicit and
> > > more clear.
> >
> > OK.
> >
> > But, I have one last comment about this function -- I saw there are already
> > other functions that iterate max_logical_replication_workers like this looking
> > for things:
> > - logicalrep_worker_find
> > - logicalrep_workers_find
> > - logicalrep_worker_launch
> > - logicalrep_sync_worker_count
> >
> > So I felt this new function (currently called GetLeaderApplyWorkerPid) ought
> > to be named similarly to those ones. e.g. call it something like
> > "logicalrep_worker_find_pa_leader_pid".
> >
>
> I am not sure we can use the name, because currently all the API name in launcher that
> used by other module(not related to subscription) are like
> AxxBxx style(see the functions in logicallauncher.h).
> logicalrep_worker_xxx style functions are currently only declared in
> worker_internal.h.
>

OK. I didn't know there was another header convention that you were
following. In that case, it is fine to leave the name as-is.

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