Re: NOT IN subquery optimization - Mailing list pgsql-hackers

From David Rowley
Subject Re: NOT IN subquery optimization
Date
Msg-id CAKJS1f-w4RfFs_3A02p=1wb85JT8EuRNL6w=cjwkKFQT6-M=5g@mail.gmail.com
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In response to Re: NOT IN subquery optimization  (Tom Lane <tgl@sss.pgh.pa.us>)
Responses Re: NOT IN subquery optimization
List pgsql-hackers
On Mon, 4 Mar 2019 at 04:42, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>
> David Rowley <david.rowley@2ndquadrant.com> writes:
> > On Sun, 3 Mar 2019 at 17:11, Tom Lane <tgl@sss.pgh.pa.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/
 PostgreSQL Development, 24x7 Support, Training & Services


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