Re: [POC] Faster processing at Gather node

On Fri, Nov 10, 2017 at 12:05 AM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> On Thu, Nov 9, 2017 at 12:08 AM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>> This change looks suspicious to me. I think here we can't use the
>> tupDesc constructed from targetlist. One problem, I could see is that
>> the check for hasOid setting in tlist_matches_tupdesc won't give the
>> correct answer. In case of the scan, we use the tuple descriptor
>> stored in relation descriptor which will allow us to take the right
>> decision in tlist_matches_tupdesc. If you try the statement CREATE
>> TABLE as_select1 AS SELECT * FROM pg_class WHERE relkind = 'r'; in
>> force_parallel_mode=regress, then you can reproduce the problem I am
>> trying to highlight.
>
> I tried this, but nothing seemed to be obviously broken. Then I
> realized that the CREATE TABLE command wasn't using parallelism, so I
> retried with parallel_setup_cost = 0, parallel_tuple_cost = 0, and
> min_parallel_table_scan_size = 0. That got it to use parallel query,
> but I still don't see anything broken. Can you clarify further?
>

Have you set force_parallel_mode=regress; before running the
statement? If so, then why you need to tune other parallel query
related parameters?

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