Horton

Re: postgres_fdw: oddity in costing aggregate pushdown paths

Etsuro Fujita <fujita.etsuro@lab.ntt.co.jp>

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From: Etsuro Fujita <fujita.etsuro@lab.ntt.co.jp>
To: Pg Hackers <pgsql-hackers@postgresql.org>
Date: 2018-11-30T09:51:29Z
Lists: pgsql-hackers

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(2018/11/28 13:38), Etsuro Fujita wrote:
> BTW another thing I noticed is this comment on costing aggregate
> pushdown paths using local statistics in estimate_path_cost_size:
> 
>               * Also, core does not care about costing HAVING expressions and
>               * adding that to the costs.  So similarly, here too we are not
>               * considering remote and local conditions for costing.
> 
> I think this was true when aggregate pushdown went in, but isn't anymore
> because of commit 7b6c07547190f056b0464098bb5a2247129d7aa2.  So we
> should update estimate_path_cost_size so that it accounts for the
> selectivity and cost of the HAVING expressions as well?

There seems to be no objections, I updated the patch as such.  Attached
is an updated version of the patch.

Best regards,
Etsuro Fujita

Commits

  1. postgres_fdw: Account for tlist eval costs in estimate_path_cost_size().

  2. postgres_fdw: Improve cost and size estimation for aggregate pushdown.

  3. Teach planner to account for HAVING quals in aggregation plan nodes.