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

On Wed, Dec 9, 2020 at 10:11 AM Greg Nancarrow <gregn4422(at)gmail(dot)com> wrote:
>
> On Wed, Dec 9, 2020 at 1:35 AM vignesh C <vignesh21(at)gmail(dot)com> wrote:
> >
> > Most of the code present in
> > v9-0001-Enable-parallel-SELECT-for-INSERT-INTO-.-SELECT.patch is
> > applicable for parallel copy patch also. The patch in this thread
> > handles the check for PROPARALLEL_UNSAFE, we could slightly make it
> > generic by handling like the comments below, that way this parallel
> > safety checks can be used based on the value set in
> > max_parallel_hazard_context. There is nothing wrong with the changes,
> > I'm providing these comments so that this patch can be generalized for
> > parallel checks and the same can also be used by parallel copy.
>
> Hi Vignesh,
>
> You are absolutely right in pointing that out, the code was taking
> short-cuts knowing that for Parallel Insert,
> "max_parallel_hazard_context.max_interesting" had been set to
> PROPARALLEL_UNSAFE, which doesn't allow that code to be generically
> re-used by other callers.
>
> I've attached a new set of patches that includes your suggested improvements.

I was going through v10-0001 patch where we are parallelizing only the
select part.

+ /*
+ * UPDATE is not currently supported in parallel-mode, so prohibit
+ * INSERT...ON CONFLICT...DO UPDATE...
+ */
+ if (parse->onConflict != NULL && parse->onConflict->action ==
ONCONFLICT_UPDATE)
+ return PROPARALLEL_UNSAFE;

I understand that we can now allow updates from the worker, but what
is the problem if we allow the parallel select even if there is an
update in the leader?

--
Regards,
Dilip Kumar
EnterpriseDB: http://www.enterprisedb.com