Re: postgres_fdw join pushdown (was Re: Custom/Foreign-Join-APIs)
| От | Ashutosh Bapat |
|---|---|
| Тема | Re: postgres_fdw join pushdown (was Re: Custom/Foreign-Join-APIs) |
| Дата | |
| Msg-id | CAFjFpRc8WOO8CkK=aW=YP3w6K9SWiR_Q3X4-B6i0FRLYZOekhA@mail.gmail.com обсуждение исходный текст |
| Ответ на | Re: postgres_fdw join pushdown (was Re: Custom/Foreign-Join-APIs) (Etsuro Fujita <fujita.etsuro@lab.ntt.co.jp>) |
| Список | pgsql-hackers |
The latest version of the postgres_fdw join pushdown patch will support only the unparameterized-path case, so we don't have to consider this, but why do you think the superiority of parameterizations is preserved between remote joining and local joining?If so, my concern is, the helper function probably wouldn't
extend to the parameterized-foreign-join-path cases, though that
would work well for the unparameterized-foreign-join-path cases. We
don't support parameterized-foreign-join paths for 9.6?If we do not find a local path with given parameterization, it means
there are other local parameterized paths which are superior to it. This
possibly indicates that there will be foreign join parameterised paths
which are superior to this parameterized path, so we basically do not
create foreign join path with that parameterization.
AFAIU, parameterization for local paths bubbles up from base relations. For foreign relations, we calculate the cost of parameterization when use_remote_estimate is ON, which means it's accurate. So, except that we will get clause selectivity wrong (if foreign tables were analyzed regularly even that won't be the case, I guess) resulting in some small sway in the costs as compared to those of parameterized foreign join paths. So, I am guessing that the local estimates for parameterized join paths would be closer to parameterized foreign paths (if we were to produce those). Hence my statement. There is always a possibility that those two costs are way too different, hence I have used phrase "possibly" there. I could be wrong.
Best Wishes,
Ashutosh Bapat
EnterpriseDB Corporation
The Postgres Database Company
Ashutosh Bapat
EnterpriseDB Corporation
The Postgres Database Company
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