From: Tom Lane <tgl@sss.pgh.pa.us>
To: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Cc: Andreas Seltenreich <seltenreich@gmx.de>
Cc: pgsql-hackers@lists.postgresql.org, Tomas Vondra <tomas.vondra@postgresql.org>
Subject: Re: [sqlsmith] Crash in mcv_get_match_bitmap
Date: Wed, 10 Jul 2019 18:48:16 -0400
Message-ID: <19586.1562798896@sss.pgh.pa.us> (raw)
In-Reply-To: <20190710215904.ncaqlswrylliisv3@development>
References: <8736jdhbhc.fsf@ansel.ydns.eu>
<15097.1562792274@sss.pgh.pa.us>
<20190710212609.5mrl7hltbozoxpq7@development>
<17042.1562795124@sss.pgh.pa.us>
<20190710215904.ncaqlswrylliisv3@development>
Oh ... while we're piling on here, it just sunk into me that
mcv_get_match_bitmap is deciding what the semantics of an operator
are by seeing what it's using for a selectivity estimator.
That is just absolutely, completely wrong. For starters, it
means that the whole mechanism fails for any operator that wants
to use a specialized estimator --- hardly an unreasonable thing
to do. For another, it's going to be pretty unreliable for
extensions, because I do not think they're all careful about using
the right estimator --- a lot of 'em probably still haven't adapted
to the introduction of separate <= / >= estimators, for instance.
The right way to determine operator semantics is to look to see
whether they are in a btree opclass. That's what the rest of the
planner does, and there is no good reason for the mcv code to
do it some other way.
regards, tom lane
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To: pgsql-hackers@postgresql.org
Cc: tgl@sss.pgh.pa.us, tomas.vondra@2ndquadrant.com, seltenreich@gmx.de, tomas.vondra@postgresql.org
Subject: Re: [sqlsmith] Crash in mcv_get_match_bitmap
In-Reply-To: <19586.1562798896@sss.pgh.pa.us>
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