Re: extended operator classes vs. type interfaces

On Fri, Apr 9, 2010 at 5:49 PM, Jeff Davis <pgsql@j-davis.com> wrote:
> On Thu, 2010-04-08 at 22:29 -0400, Robert Haas wrote:
>> 1. knngist wants to use index scans to speed up queries of the form
>> SELECT ... ORDER BY <column> <op> <constant> (as opposed to the
>> existing machinery which only knows how to use an index for SELECT ...
>> ORDER BY <column>).
>> 2. Window functions want to define windows over a range of values
>> defined by the underlying data type.  To do this, we need to define
>> what addition and subtraction mean for a particular data type.
>> 3. Jeff Davis is interested in implementing range types.  When the
>> underlying base type is discrete, e.g. integers, you can say that
>> [1,3] = [1,4), but only if you know that 3 and 4 are consecutive (in
>> that order).
>
> To give some context, I started a thread a while ago:
>
> http://archives.postgresql.org/pgsql-hackers/2009-10/msg01403.php
>
> Tom provided some interesting suggestions in that thread, but I'm not
> sure they would work for #1 or #2.

<rereads thread>

The "map && to <<" case is interesting.  It doesn't seem like it's
really a good candidate for type interfaces, because you you're not
really looking for "the" strictly-left-of operator; you're looking for
the strictly-left-of operator associated with the overlaps operator
actually specified.  And ideally there might be an index strategy
number available for <<, too, so that you could consider doing an
index scan instead of a sort, but not necessarily.

...Robert