Horton

Re: [sqlsmith] Crash in mcv_get_match_bitmap

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Cc: Andreas Seltenreich <seltenreich@gmx.de>, pgsql-hackers@lists.postgresql.org, Tomas Vondra <tomas.vondra@postgresql.org>
Date: 2019-07-10T22:48:16Z
Lists: pgsql-hackers 
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

Commits

  1. Use column collation for extended statistics

  2. Rework examine_opclause_expression to use varonleft

  3. Fix handling of NULLs in MCV items and constants

  4. Fix handling of opclauses in extended statistics

  5. Remove unnecessary TYPECACHE_GT_OPR lookup

  6. Simplify bitmap updates in multivariate MCV code

  7. Make pg_statistic and related code account more honestly for collations.