Re: POC, WIP: OR-clause support for indexes

On Mon, Oct 7, 2024 at 12:02 PM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Peter Geoghegan <pg(at)bowt(dot)ie> writes:
> > To be clear, I don't think that it's essential that we have equivalent
> > behavior in those cases where the patch applies its transformations. I
> > have no objections to committing the patch without any handling for
> > that.
>
> Oy. I don't agree with that *at all*. An "optimization" that changes
> query semantics is going to be widely seen as a bug.

I think that you must have misinterpreted what I meant by "equivalent
behavior". The context was important. I really meant: "Ideally, the
patch's transformations would produce an equivalent execution strategy
to what we already get in when IN() is used directly, *even in the
presence of constants of mixed though related types*. Ideally, the
final patch would somehow be able to generate a SAOP with one array of
the same common type in cases where an analogous IN() query can do the
same. But I'm not going to insist on adding something for that now."

Importantly, I meant equivalent outcome in terms of execution
strategy, across similar queries where the patch sometimes succeeds in
generating a SAOP, and sometimes fails -- I wasn't trying to say
anything about query semantics. This wasn't intended to be a rigorous
argument (if it was then I'd have explained why my detailed and
rigorous proposal didn't break query semantics).

--
Peter Geoghegan