On Wed, Apr 26, 2017 at 8:46 PM, Bruce Momjian <bruce@momjian.us> wrote:
> On Wed, Apr 26, 2017 at 07:38:05PM +0530, Amit Kapila wrote:
>> >> I have already mentioned the commit id (5e6d8d2b). Text can be "Allow
>> >> queries containing subplans to execute in parallel". We should also
>> >> mention in some way that this applies only when the query contains
>> >> uncorrelated subplan.
>> >
>> > Sorry but I don't know what that means, and if I don't know, others
>> > might not either.
>> >
>>
>> regression=# explain (costs off) select count(*) from tenk1 where
>> (two, four) not in (select hundred, thousand from tenk2 where
>> thousand > 100);
>> QUERY PLAN
>> ------------------------------------------------------
>> Finalize Aggregate
>> -> Gather
>> Workers Planned: 2
>> -> Partial Aggregate
>> -> Parallel Seq Scan on tenk1
>> Filter: (NOT (hashed SubPlan 1))
>> SubPlan 1
>> -> Seq Scan on tenk2
>> Filter: (thousand > 100)
>> (9 rows)
>>
>
> Oh, so non-correlated subqueries can be run in parallel. Yes, that is
> something we should have in the release notes. How is this?
>
> Author: Robert Haas <rhaas@postgresql.org>
> 2017-02-14 [5e6d8d2bb] Allow parallel workers to execute subplans.
>
> Allow non-correlated subqueries to be run in parallel (Amit Kapila)
>
Looks good to me.
--
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com
