Re: [sqlsmith] Crash in mcv_get_match_bitmap

On Wed, Jul 10, 2019 at 04:57:54PM -0400, Tom Lane wrote:
>Andreas Seltenreich <seltenreich@gmx.de> writes:
>> running sqlsmith on the regression database of REL_12_STABLE at
>> ff597b656f yielded a crash in mcv_get_match_bitmap.  I can reproduce it
>> with the following query on the regression database:
>>     select filler1 from mcv_lists where a is not null and (select 42) <= c;
>
>Seems to be the same problem I just complained of in the other
>thread: mcv_get_match_bitmap has an untenable assumption that
>"is a pseudoconstant" means "is a Const".
>

Yeah, that's a bug. Will fix (not sure how yet).

BTW which other thread? I don't see any other threads mentioning this
function.

>I notice it's also assuming that the Const must be non-null.
>It's not really easy to crash it that way, because if you just
>write "null <= c" that'll get reduced to constant-NULL earlier.
>But I bet there's a way.
>

Hmmm, I did not think of that.


regards

-- 
Tomas Vondra                  http://www.2ndQuadrant.com
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