Re: Pg17 Crash in Planning (Arrays + Casting + UDF)

On Wed, Oct 09, 2024 at 04:21:53PM -0400, Tom Lane wrote:
> Paul Ramsey <pramsey(at)cleverelephant(dot)ca> writes:
>> This extremely odd case [2] came in via a report using a lot of PostGIS
>> functions, but it can be reconfigured into a pure-PostgreSQL crasher
>> [1].
>
> Thanks for the report! Looks like estimate_array_length() is
> incautiously assuming that the "root" pointer it receives will
> never be NULL.

Yup, git-bisect points me to commit 9391f71.

> We could change their signatures ... but it's explicitly documented
> that eval_const_expressions allows NULL for root, so there would
> presumably still be code paths that'd fail. It looks like the only
> safe fix is to ensure that estimate_array_length will cope with NULL
> for root.

Do you mean something like this?

- else if (arrayexpr)
+ else if (arrayexpr && root != NULL)

That'd at least be no worse than how it worked before
estimate_array_length() tried to use statistics, so that seems reasonable
to me.

--
nathan