Re: [HACKERS] Partition-wise aggregation/grouping

On Wed, Apr 26, 2017 at 6:28 AM, Antonin Houska <ah@cybertec.at> wrote:
> Attached is a diff that contains both patches merged. This is just to prove my
> assumption, details to be elaborated later. The scripts attached produce the
> following plan in my environment:
>
>                    QUERY PLAN
> ------------------------------------------------
>  Parallel Finalize HashAggregate
>    Group Key: b_1.j
>    ->  Append
>          ->  Parallel Partial HashAggregate
>                Group Key: b_1.j
>                ->  Hash Join
>                      Hash Cond: (b_1.j = c_1.k)
>                      ->  Seq Scan on b_1
>                      ->  Hash
>                            ->  Seq Scan on c_1
>          ->  Parallel Partial HashAggregate
>                Group Key: b_2.j
>                ->  Hash Join
>                      Hash Cond: (b_2.j = c_2.k)
>                      ->  Seq Scan on b_2
>                      ->  Hash
>                            ->  Seq Scan on c_2

Well, I'm confused.  I see that there's a relationship between what
Antonin is trying to do and what Jeevan is trying to do, but I can't
figure out whether one is a subset of the other, whether they're both
orthogonal, or something else.  This plan looks similar to what I
would expect Jeevan's patch to produce, except i have no idea what
"Parallel" would mean in a plan that contains no Gather node.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
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