Re: Get more from indices.

# Sorry for accidentialy sending the previous mail unfinished.

## ...and I seem to have bombed uncertain files off out of my
## home directory by accident, too :(

=====
Hi, sorry for the absense. I've been back.

Thank you for continuing this discussion.

Attached is the patch following the discussion below.

> >> (2014/04/10 0:08), Tom Lane wrote:
> >>> TBH I think that's barely the tip of the iceberg of cases where this
> >>> patch will get the wrong answer.
> >
> >>> Also, I don't see it doing anything to check the ordering
> >>> of multiple index columns
> >
> >> I think that the following code in index_pathkeys_are_extensible() would
> >> check the ordering:
> >> + if (!pathkeys_contained_in(pathkeys, root->query_pathkeys))
> >> + return false;
> >
> > Hm ... if you're relying on that, then what's the point of the new loop
> > at all?
>
> The point is that from the discussion [1], we allow the index pathkeys
> to be extended to query_pathkeys if each *remaining* pathkey in
> query_pathkey is a Var belonging to the indexed relation. The code is
> confusing, though. Sorry, that is my faults.

Hmm, I found that the iterations for the part that already
checked by pathkeys_contained_in are not only useless but a bit
heavy. And the loop seems a little verbose. I did for the patch,
in index_pathkeys_are_extensible,

- Avoiding duplicate check with pathkeys_contained_in.

I put similar code to list_nth_cell since it is not exposed
outside of list.c.

- Add comment to clarify the purpose of the loop.

- Simplify the check for the "remaining" keycolumns

I think this makes some things clearer.

regards,

--
Kyotaro Horiguchi
NTT Open Source Software Center