Re: postgres_fdw: oddity in costing aggregate pushdown paths

From: Etsuro Fujita <fujita(dot)etsuro(at)lab(dot)ntt(dot)co(dot)jp>
To: Pg Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: postgres_fdw: oddity in costing aggregate pushdown paths
Date: 2018-12-28 08:28:11
Message-ID: 5C25DE9B.5010000@lab.ntt.co.jp
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(2018/12/04 17:24), Etsuro Fujita wrote:
> (2018/12/03 20:20), Etsuro Fujita wrote:
>> (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.
>
> Done after fixing typos in the commit message.

I noticed that I forgot to modify the cost for evaluating the PathTarget
for each output row accordingly to this change :(. Attached is a patch
for that.

Best regards,
Etsuro Fujita

Attachment Content-Type Size
fix-postgres-fdw-grouping-path-cost.patch text/x-patch 804 bytes

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