Re: Parallel INSERT (INTO ... SELECT ...)

On Fri, Mar 5, 2021 at 5:07 AM Greg Nancarrow <gregn4422(at)gmail(dot)com> wrote:
>
> On Thu, Mar 4, 2021 at 11:05 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> >
> > On Thu, Mar 4, 2021 at 5:24 PM Greg Nancarrow <gregn4422(at)gmail(dot)com> wrote:
> > >
> > > On Thu, Mar 4, 2021 at 10:07 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> > > >
> > >
> > > >Also, in
> > > > standard_planner, we should add these partitionOids only for
> > > > parallel-mode.
> > > >
> > >
> > > It is doing that in v20 patch (what makes you think it isn't?).
> > >
> >
> > The below code snippet:
> > + /* For AcquireExecutorLocks(). */
> > + if (IsModifySupportedInParallelMode(parse->commandType))
> > + result->partitionOids = glob->partitionOids;
> >
> > I understand that you have a check for the parallel mode in
> > AcquireExecutorLocks but why can't we have it before adding that to
> > planned statement
> >
>
> OK, I think I'm on the same wavelength now (sorry, I didn't realise
> you're talking about PlannedStmt).
>
> What I believe you're suggesting is in the planner where
> partitionOids are "added" to the returned PlannedStmt, they should
> only be added if glob->parallelModeNeeded is true:.
>
> i.e.
>
> /* For AcquireExecutorLocks(). */
> if (glob->partitionOids != NIL && glob->parallelModeNeeded)
> result->partitionOids = glob->partitionOids;
>
> (seems reasonable to me, as then it will match the condition for which
> glob->partitionOids are added to glob->relationOids)
>
> then in plancache.c the check on parallelModeNeeded can be removed:
>
> /* Lock partitions ahead of modifying them in parallel mode. */
> if (rti == resultRelation &&
> plannedstmt->partitionOids != NIL)
> AcquireExecutorLocksOnPartitions(plannedstmt->partitionOids,
> rte->rellockmode, acquire);
>
> Let me know if this matches what you were thinking.
>

Yes, that is what I was thinking. But I have another question as well
regarding tracking these partitions at two places (once in
plannedstmt->relationOids and the second time in
plannedstmt->partitionOids). I think it is better if you can prepare a
patch with all the comments raised till now leaving this last question
aside.

--
With Regards,
Amit Kapila.