Re: postgres_fdw: oddity in costing aggregate pushdown paths

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

From: Etsuro Fujita <fujita.etsuro@lab.ntt.co.jp>
To: Pg Hackers <pgsql-hackers@postgresql.org>
Date: 2018-12-03T11:20:32Z
Lists: pgsql-hackers

Attachments

(2018/11/30 18:51), Etsuro Fujita wrote:
> (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.

I revised some comments a bit and added the commit message.  Attached is
an updated patch.  If there are no objections, I'll apply this to HEAD only.

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.