Re: Partial Aggregation / GROUP BY before JOIN
| От | David Rowley |
|---|---|
| Тема | Re: Partial Aggregation / GROUP BY before JOIN |
| Дата | |
| Msg-id | CAKJS1f8cw_Sw1WKa7FwC8T7C8FK4=jusYy4038yfwtATA3xg1w@mail.gmail.com обсуждение исходный текст |
| Ответ на | Re: Partial Aggregation / GROUP BY before JOIN (Amit Langote <Langote_Amit_f8@lab.ntt.co.jp>) |
| Ответы |
Re: Partial Aggregation / GROUP BY before JOIN
|
| Список | pgsql-hackers |
On 28 September 2015 at 23:17, Amit Langote <Langote_Amit_f8@lab.ntt.co.jp> wrote:
On 2015/09/28 17:04, David Rowley wrote:
> On 28 September 2015 at 20:36, Amit Langote <Langote_Amit_f8@lab.ntt.co.jp>
> wrote:
>
>>
>> Did you perhaps attach a version of the patch you didn't intend to?
>>
>
> Oops. It seems so.
>
> Please find the correct version attached.
Thanks, this one works fine.
By the way, you may have noticed that the append_rel_list would be broken
if the proposed optimization is applied to a appendrel parent.
CREATE TABLE sale_1() INHERITS(sale);
CREATE TABLE sale_2() INHERITS(sale);
EXPLAIN SELECT count(*) FROM sale;
QUERY PLAN
------------------------------------------------------
Finalize Aggregate (cost=0.01..0.02 rows=1 width=0)
-> Result (cost=0.00..0.01 rows=1 width=0)
One-Time Filter: false
(3 rows)
Thanks. I've changed this locally to disable the optimisation in this case.
Moreover, would partial aggregation work below Append?
Do you mean for cases like:
create table a as select x.x a from generate_series(1,1000000) x(x);
select sum(a) from (select a from a union all select a from a) a;
to allow the aggregation to happen before the append?
On testing this I do see that writing the query as:
select sum(a) from (select sum(a) a from a union all select sum(a) from a) a;
causes it to execute marginally faster. 174.280 ms vs 153.498 ms on my laptop.
However pushing aggregation below Append nodes is not something I'm aiming to do for this patch.
--
David Rowley http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
В списке pgsql-hackers по дате отправления: