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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Alexander Korotkov <a.korotkov@postgrespro.ru>
Cc: Julien Rouhaud <rjuju123@gmail.com>
Cc: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Cc: Nikita Glukhov <n.gluhov@postgrespro.ru>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Cc: Thomas Munro <thomas.munro@gmail.com>
Cc: Marc Cousin <cousinmarc@gmail.com>
Subject: Re: Avoid full GIN index scan when possible
Date: Fri, 17 Jan 2020 16:48:10 -0500
Message-ID: <18357.1579297690@sss.pgh.pa.us> (raw)
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Alexander Korotkov <a.korotkov@postgrespro.ru> writes:
> On Wed, Jan 15, 2020 at 2:03 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> Hmm ... yeah, these test cases are not large enough to exercise any
>> lossy-page cases, are they?  I doubt we should try to make a new regression
>> test that is that big.  (But if there is one already, maybe we could add
>> more test queries with it, instead of creating whole new tables?)

> I've checked that none of existing tests for GIN can produce lossy
> bitmap page with minimal work_mem = '64kB'.  I've tried to generate
> sample table with single integer column to get lossy page.  It appears
> that we need at least 231425 rows to get it.  With wider rows, we
> would need less number of rows, but I think total heap size wouldn't
> be less.
> So, I think we don't need so huge regression test to exercise this corner case.

Ugh.  Yeah, I don't want a regression test case that big either.

v15 looks good to me.

			regards, tom lane





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