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

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.

Best regards,
Hou zj