Re: Problems with plan estimates in postgres_fdw

From: Etsuro Fujita <fujita(dot)etsuro(at)lab(dot)ntt(dot)co(dot)jp>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Andrew Gierth <andrew(at)tao11(dot)riddles(dot)org(dot)uk>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Problems with plan estimates in postgres_fdw
Date: 2019-01-30 11:10:41
Message-ID: 5C518631.5080401@lab.ntt.co.jp
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(2018/12/28 15:50), Etsuro Fujita wrote:
> Attached is a new version of the
> patch.

Here is an updated version of the patch set. Changes are:

* In the previous version, LIMIT without OFFSET was not performed
remotely as the costs was calculated the same as the costs of performing
it locally. (Actually, such LIMIT was performed remotely in a case in
the postgres_fdw regression test, but that was due to a bug :(.) I
think we should prefer performing such LIMIT remotely as that avoids
extra row fetches from the remote that performing it locally might
cause, so I tweaked the costs estimated in estimate_path_cost_size(), to
ensure that we'll prefer performing such LIMIT remotely. (I fixed the
mentioned bug as well.)

* I fixed another bug in adjusting the costs of pre-sorted
foreign-grouping paths.

* I tweaked comments, and rebased the patch set against the latest HEAD.

Best regards,
Etsuro Fujita

Attachment Content-Type Size
0001-postgres_fdw-Perform-UPPERREL_ORDERED-step-remotely-v3.patch text/x-patch 44.2 KB
0002-postgres_fdw-Perform-UPPERREL_FINAL-step-remotely-v3.patch text/x-patch 101.7 KB

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