Re: Bug in row_number() optimization

On Sat, 26 Nov 2022 at 05:19, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>
> Sergey Shinderuk <s.shinderuk@postgrespro.ru> writes:
> > What about user-defined operators? I created my own <= operator for int8
> > which returns true on null input, and put it in a btree operator class.
> > Admittedly, it's weird that (null <= 1) evaluates to true. But does it
> > violate  the contract of the btree operator class or something? Didn't
> > find a clear answer in the docs.
>
> It's pretty unlikely that this would work during an actual index scan.
> I'm fairly sure that btree (and other index AMs) have hard-wired
> assumptions that index operators are strict.

If we're worried about that then we could just restrict this
optimization to only work with strict quals.

The proposal to copy the datums into the query context does not seem
to me to be a good idea. If there are a large number of partitions
then it sounds like we'll leak lots of memory.  We could invent some
partition context that we reset after each partition, but that's
probably more complexity than it would be worth.

I've attached a draft patch to move the code to nullify the aggregate
results so that's only done once per partition and adjusted the
planner to limit this to strict quals.

David