Re: Improve planner cost estimations for alternative subplans
| От | Melanie Plageman |
|---|---|
| Тема | Re: Improve planner cost estimations for alternative subplans |
| Дата | |
| Msg-id | CAAKRu_ZAKdRa5CydfvSRwC_xwwboXEiqitXK4TMppHOcx7uu5A@mail.gmail.com обсуждение исходный текст |
| Ответ на | Improve planner cost estimations for alternative subplans (Alexey Bashtanov <bashtanov@imap.cc>) |
| Ответы |
Re: Improve planner cost estimations for alternative subplans
|
| Список | pgsql-hackers |
On Fri, Jun 5, 2020 at 9:08 AM Alexey Bashtanov <bashtanov@imap.cc> wrote:
In [1] we found a situation where it leads to a suboptimal plan,
as it bloats the overall cost into large figures,
a decision related to an outer part of the plan look negligible to the
planner,
and as a result it doesn't elaborate on choosing the optimal one.
I've just started looking at this patch today, but I was wondering if
you might include a test case which minimally reproduces the original
problem you had.
The only plan diff I see is in updatable_views.sql, and it doesn't
illustrate the problem as well as a more straightforward SELECT query
with EXISTS sublink might.
-- you might include a test case which minimally reproduces the original
problem you had.
The only plan diff I see is in updatable_views.sql, and it doesn't
illustrate the problem as well as a more straightforward SELECT query
with EXISTS sublink might.
After putting in some logging, I see that there are only a
few non-catalog queries which exercise this code path.
This query from groupingsets.sql is an example of one such query:
select ten, sum(distinct four) from onek a
group by grouping sets((ten,four),(ten))
having exists (select 1 from onek b where sum(distinct a.four) = b.four);
few non-catalog queries which exercise this code path.
This query from groupingsets.sql is an example of one such query:
select ten, sum(distinct four) from onek a
group by grouping sets((ten,four),(ten))
having exists (select 1 from onek b where sum(distinct a.four) = b.four);
But, the chosen plan for this query stays the same.
It would be helpful to see a query where a different plan is chosen
because of this change that is not from updatable_views.sql.
It would be helpful to see a query where a different plan is chosen
because of this change that is not from updatable_views.sql.
Melanie Plageman
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