Re: EXPLAIN ANALYZE for parallel query doesn't report the SortMethod information.

On Thu, Jul 7, 2016 at 7:37 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> writes:
>> On Thu, Jul 7, 2016 at 1:23 PM, Fujii Masao <masao(dot)fujii(at)gmail(dot)com> wrote:
>>> I found $SUBJECT while trying to test parallel queries. Is this a bug?
>
> Presumably the instrumentation data needed for that is not getting
> returned from the worker to the leader. I would bet there's a lot
> of other plan-node-specific data that doesn't work either.
>
>> I think this can never happen for force_parallel_mode TO off, because
>> we don't generate a gather on top of sort node. The reason why we are
>> able to push Sort below gather, because it is marked as parallel_safe
>> (create_sort_path). I think we should not mark it as parallel_safe.
>
> That seems rather ridiculous. An oversight in managing EXPLAIN data
> is not a sufficient reason to cripple parallel query.
>

I am analyzing that point only and you seems to be right that we have
missed to propagate some information. We have taken care of
instrumentation information to be propagated back to leader, but it
seems there are other things that needs to be taken care in that area.

--
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com