Re: NOT IN subquery optimization

On Mon, 4 Mar 2019 at 04:42, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>
> David Rowley <david(dot)rowley(at)2ndquadrant(dot)com> writes:
> > On Sun, 3 Mar 2019 at 17:11, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> >> (At the code level, this is implicit in the fact that the comparison
> >> function will be called via FunctionCall2Coll or a sibling, and those
> >> all throw an error if the called function returns NULL.)
>
> > Ah okay. I can get it to misbehave by setting fcinfo->isnull = true in
> > the debugger from int4eq(). I see the NULL result there is not
> > verified as that's just translated into "false" by ExecInterpExpr()'s
> > EEOP_QUAL case. If you're saying something doing that is
> > fundamentally broken, then I guess we're okay.
>
> No, what I'm thinking of is this bit in _bt_compare:
>
> result = DatumGetInt32(FunctionCall2Coll(&scankey->sk_func,
> scankey->sk_collation,
> datum,
> scankey->sk_argument));
>
> You absolutely will get errors during btree insertions and searches
> if a datatype's btree comparison functions ever return NULL (for
> non-NULL inputs).

I understand this is the case if an index happens to be used, but
there's no guarantee that's going to be the case. I was looking at the
case where an index was not used.

--
David Rowley http://www.2ndQuadrant.com/
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