Re: Avoid full GIN index scan when possible

From: Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Nikita Glukhov <n(dot)gluhov(at)postgrespro(dot)ru>, Alexander Korotkov <a(dot)korotkov(at)postgrespro(dot)ru>, Julien Rouhaud <rjuju123(at)gmail(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>, Thomas Munro <thomas(dot)munro(at)gmail(dot)com>, Marc Cousin <cousinmarc(at)gmail(dot)com>, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>
Subject: Re: Avoid full GIN index scan when possible
Date: 2019-09-02 22:20:01
Message-ID: 20190902222001.GA2704@alvherre.pgsql
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On 2019-Aug-07, Tom Lane wrote:

> I think this would be committable as it stands, except that replacing
> an ALL scan with an EVERYTHING scan could be a performance regression
> if the index contains many null items. We need to do something about
> that before committing.

Nikita, any word on getting this change done?

> Unfortunately I'm not sold on either 0002 or 0003 as they stand;
> they seem overly complicated, I'm not convinced they're correct,
> and you haven't really provided examples showing that all this
> extra complexity is worthwhile.

I suppose we should call ourselves satisfied if we get 0001 done during
this cycle (or at least this commitfest). Further refinement can be had
in the future, as needed -- even within pg13, if Nikita or anybody else
wants to tackle Tom's suggested approaches (or something completely new,
or just contest Tom's points) quickly enough. But I don't think we need
that in order to call this CF entry committed.

Álvaro Herrera
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

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