Re: BUG #17618: unnecessary filter column <> text even after adding index

On Sat, Sep 24, 2022 at 8:04 AM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> Richard Guo <guofenglinux(at)gmail(dot)com> writes:
> > We should have already done that long before. It seems afterwards we may
> > do additional transformation on indexquals. In this case with a boolean
> > index, I can see we convert the indexqual to form 'indexkey = TRUE' in
> > match_boolean_index_clause.
>
> Of course, but what about that transformation would introduce something
> that eval_const_expressions could simplify? (Actually, now that I think
> about it, I think eval_const_expressions would break it completely because
> it'd re-canonicalize the expression as just 'indexkey', exactly what we
> don't want here.) In any case, if there's something between the
> eval_const_expressions pass and createplan.c that introduces simplifiable
> expressions, I think it's on that something's head to re-simplify; we
> don't want to do something so expensive in a main code path if it's
> usually going to be a complete waste.

Yeah, I agree that running eval_const_expressions here is expensive.
Maybe we can just do the reverse transformation in
create_bitmap_scan_plan against what we do for boolean index in
match_boolean_index_clause?

I think it's necessary to re-simplify the indexquals here, otherwise we
may fail to compare scan_clauses to indexquals correctly.

Thanks
Richard