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

On Sat, Sep 24, 2022 at 8:41 AM Richard Guo <guofenglinux@gmail.com> wrote:

>
> On Sat, Sep 24, 2022 at 8:04 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:
>
>> Richard Guo <guofenglinux@gmail.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?
>

Following this idea, I come up with v2 patch. Is this the right
direction to go?

Thanks
Richard