From: Tom Lane <tgl@sss.pgh.pa.us>
To: Alexander Korotkov <a.korotkov@postgrespro.ru>
cc: Julien Rouhaud <rjuju123@gmail.com>,
        Tomas Vondra <tomas.vondra@2ndquadrant.com>,
        Nikita Glukhov <n.gluhov@postgrespro.ru>,
        PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>,
        Thomas Munro <thomas.munro@gmail.com>,
        Marc Cousin <cousinmarc@gmail.com>
Subject: Re: Avoid full GIN index scan when possible
In-reply-to: 
 <CAPpHfdtvH7EtVJ_J-LMV-YieHc93mdYANdP5bUL7MwVQwMAFVA@mail.gmail.com>
References: 
 <CAOBaU_b3u1xpoESb2JD6dQ4V7fhwmbfOFW5PiadZHJX6bNdnfw@mail.gmail.com>
 <17590.1564685940@sss.pgh.pa.us>
 <CAPpHfdvfK+Zk=MjjC1M_66+ALD+vdR6BG3quoFAZzjL6hNv-NQ@mail.gmail.com>
 <19189.1564687723@sss.pgh.pa.us>
 <a6e1564e-98c8-e420-cfaf-0309316c4910@postgrespro.ru>
 <19438.1565209940@sss.pgh.pa.us>
 <f2889144-db1d-e3b2-db97-cfc8794cda43@postgrespro.ru>
 <CAPpHfdsXN5iq3rUwjuwtp_GRFmhq+1QAtgiywGM_6YM9PdGdMg@mail.gmail.com>
 <CAPpHfdvT_t6ShG2pvptEWceDxEnyNRsm2MxmCWWvxBzQ-pbMuw@mail.gmail.com>
 <b53614eb-6f9f-8c5c-9df8-f703b0b102b6@postgrespro.ru>
 <20200106152155.uuungi2p776p5lbk@development>
 <CAPpHfdthhf8S-UjE46hjy+g7pgGhy=hav1-BUmQq6+hKmY13nA@mail.gmail.com>
 <29242.1578670290@sss.pgh.pa.us>
 <CAPpHfdu+rcbqU1fCwvfy60uFodxwWiQqKy_2AVnq4=2SEt+2bA@mail.gmail.com>
 <CAPpHfdttREdy0H9ovJjcd5UUu1my6TS8GRNRuKpL2dTDt8o2wQ@mail.gmail.com>
 <CAOBaU_YJadWvDVO3FQ_hddaTHSreWre6hPSNw=4wY6SskrvLuA@mail.gmail.com>
 <CAPpHfdusQSm6Nx+hipY+ArU0Udr8ZYivWvoCx2AT2Yvujd=WPA@mail.gmail.com>
 <20952.157902739!
 1@sss.pgh.pa.us>
 <CAPpHfdt8vCETJy9xMAvv1QQbOnNUfMfY8-pg+XGqJ-VWq4TNmg@mail.gmail.com>
 <7614.1579043019@sss.pgh.pa.us>
 <CAPpHfdtvH7EtVJ_J-LMV-YieHc93mdYANdP5bUL7MwVQwMAFVA@mail.gmail.com>
Comments: In-reply-to Alexander Korotkov <a.korotkov@postgrespro.ru>
	message dated "Sat, 18 Jan 2020 00:33:14 +0300"
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-ID: <18356.1579297690.1@sss.pgh.pa.us>
Content-Transfer-Encoding: quoted-printable
Date: Fri, 17 Jan 2020 16:48:10 -0500
Message-ID: <18357.1579297690@sss.pgh.pa.us>
Precedence: bulk

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 regres=
sion
>> test that is that big.  (But if there is one already, maybe we could ad=
d
>> 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 =3D '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 corne=
r case.

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

v15 looks good to me.

			regards, tom lane