Horton

Re: [sqlsmith] Crash in mcv_get_match_bitmap

Tomas Vondra <tomas.vondra@2ndquadrant.com>

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From: Tomas Vondra <tomas.vondra@2ndquadrant.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Andreas Seltenreich <seltenreich@gmx.de>, pgsql-hackers@lists.postgresql.org, Tomas Vondra <tomas.vondra@postgresql.org>
Date: 2019-07-10T21:59:04Z
Lists: pgsql-hackers 
On Wed, Jul 10, 2019 at 05:45:24PM -0400, Tom Lane wrote:
>Tomas Vondra <tomas.vondra@2ndquadrant.com> writes:
>> Yeah, that's a bug. Will fix (not sure how yet).
>
>You could do worse than replace this:
>
>        ok = (NumRelids(clause) == 1) &&
>            (is_pseudo_constant_clause(lsecond(expr->args)) ||
>             (varonleft = false,
>              is_pseudo_constant_clause(linitial(expr->args))));
>
>with something like
>
>	if (IsA(linitial(expr->args), Var) &&
>	    IsA(lsecond(expr->args), Const))
>	   ok = true, varonleft = true;
>	else if (IsA(linitial(expr->args), Const) &&
>	         IsA(lsecond(expr->args), Var))
>	   ok = true, varonleft = false;
>
>Or possibly get rid of varonleft as such, and merge extraction of the
>"var" and "cst" variables into this test.
>

OK, thanks for the suggestion.

I probably also need to look at the "is compatible" test in
extended_stats.c which also looks at the clauses. It may not crash as it
does not attempt to extract the const values etc. but it likely needs to
be in sync with this part.

>BTW, I bet passing a unary-argument OpExpr also makes this code
>unhappy.

Whooops :-(


regards

-- 
Tomas Vondra                  http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

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.