GiST for range types (was Re: Range Types - typo + NULL string constructor)

On Fri, Oct 7, 2011 at 7:41 AM, Jeff Davis <pgsql(at)j-davis(dot)com> wrote:

> I'd prefer to include it in the initial patch. If the current GiST code
> is going to be replaced, then there's not much sense reviewing/testing
> it.
>
> You may need to consider unbounded and empty ranges specially. I made an
> attempt to do so in the current GiST code, and you might want to take a
> look at that first. I'm not particularly attached to my approach, but we
> should do something reasonable with unbounded and empty ranges.
>

The first thing caught my eye in existing GiST code is idea of
subtype_float. float8 has limited precision and can't respresent, for
example, varlena values good enough. Even if we have large int8 value we can
loose lower bits, but data distribution can be so that these bits are
valuable. Wouldn't it better to have function like subtype_diff_float which
returns difference between two values of subtype as an float? Using of such
function could make penalty more sensible to even small difference between
values, and accordingly more relevant.

------
With best regards,
Alexander Korotkov.