Date: Thu, 18 Jan 2018 17:25:05 +0900
From: Michael Paquier <michael.paquier@gmail.com>
To: Andrey Borodin <x4mmm@yandex-team.ru>
Cc: Kyotaro HORIGUCHI <horiguchi.kyotaro@lab.ntt.co.jp>, sk@zsrv.org,
	david@nlpgo.com, pgsql-bugs@lists.postgresql.org,
	pgsql-hackers@postgresql.org
Subject: Re: Index-only scan returns incorrect results when using a composite
 GIST index with a gist_trgm_ops column.
Message-ID: <20180118082505.GA84508@paquier.xyz>
References: <1516210494.1798.16.camel@nlpgo.com>
 <412861516217175@web38o.yandex.ru>
 <20180118.144851.24081723.horiguchi.kyotaro@lab.ntt.co.jp>
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On Thu, Jan 18, 2018 at 12:57:38PM +0500, Andrey Borodin wrote:
>> 18 =D1=8F=D0=BD=D0=B2. 2018 =D0=B3., =D0=B2 10:48, Kyotaro HORIGUCHI <ho=
riguchi.kyotaro@lab.ntt.co.jp> =D0=BD=D0=B0=D0=BF=D0=B8=D1=81=D0=B0=D0=BB(=
=D0=B0):
>>=20
>> Gist imposes the ninth strategy to perform index only scan but
>> planner is not considering that
>> ....
>> Please find the attached patch.
> I agree with you that current behavior is a bug and your patch seems corr=
ect.
> I'm a bit worried about ninth strategy words: fetch is not necessary
>> now, if opclass lacks compress methods - index only scan is
>> possible. See
>> https://github.com/postgres/postgres/commit/d3a4f89d8a3e500bd7c0b7a8a8a5=
ce1b47859128
>> for details.
>
> Though there are tests in cube and seg for that, if your patch passes
> check-world, than this behavior is not affected.=20

The proposed patch has no regression tests. If the current set is not
enough to stress the problem, you surely should add some (haven't
checked the patch in detail, sorry ;p ).
--
Michael

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