Re: Hash a ScalarArrayOpExpr whose array is fixed for one execution

Hi David, Ayoub,

Thanks again for your reviews. Could you let me know if anything
else needs to be done for v5? If you think it is ready, would you
mind marking it Ready for Committer?

I'm also adding David Rowley, since this builds on his hashed
ScalarArrayOpExpr work, in case he is interested.

Regards,
Linden

On Mon, Nov 2, 2026 at 1:44 PM Ayoub Kazar <ayoub(dot)kazar(at)data-bene(dot)io> wrote:
>
> Hi,
>
> On 01/11/2026 21:07, best xmg wrote:
>
> > Thanks for the reproducer. The root cause is the operators in your
> > test: the <> is not a valid negator of the =. The documentation [1]
> > requires "(x A y) equals NOT (x B y) for all possible inputs x, y", but
> > for a NULL input both return false. So NOT IN does not work well with
> > them even on master. The same question gets different answers,
> > depending on the length of the list:
> >
> > SELECT v <> ALL (ARRAY[1,2,3,4,5,6,7,8,9]::my_int[])
> > FROM (SELECT NULL::my_int AS v OFFSET 0) s; -- t (9 items)
> >
> > SELECT v <> ALL (ARRAY[1,2]::my_int[])
> > FROM (SELECT NULL::my_int AS v OFFSET 0) s; -- f (2 items)
> >
> > The reason: a list of 9 or more items is hashed. A hashed NOT IN looks
> > for an equal item, so it calls = and inverts the result (since PG 15,
> > 29f45e299e7). A shorter list is searched linearly, and that calls <>.
> > The two ways agree only if <> is the negator of =.
> >
> > v5 hashes $1 too, so the example in your test now gets the hashed
> > answer.
> >
> > Master's code for a hashed NOT IN depends on <> being the negator of =.
> > So does the recent fix for non-strict operators [2]. So I chose not
> > to fix it for now.
> >
> > [1]https://www.google.com/url?q=https://www.postgresql.org/docs/current/xoper-optimization.html%23XOPER-NEGATOR&source=gmail&ust=1793649679948000&sa=E
> > [2]https://www.google.com/url?q=https://postgr.es/m/A16187AE-2359-4265-9F5E-71D015EC2B2D@outlook.com&source=gmail&ust=1793649679948000&sa=E
> Indeed, missed that info, thanks!
>
>
> Regards,
> Ayoub