Re: compress method for spgist - 2

On 03/04/2015 06:58 PM, Paul Ramsey wrote:
> On Wed, Feb 25, 2015 at 6:13 AM, Heikki Linnakangas
> <hlinnakangas(at)vmware(dot)com> wrote:
>> In the original post on this, you mentioned that the PostGIS guys planned to
>> use this to store polygons, as bounding boxes
>> (http://www.postgresql.org/message-id/5447B3FF.2080406@sigaev.ru). Any idea
>> how would that work?
>
> Poorly, by hanging boxes that straddled dividing lines off the parent
> node in a big linear list. The hope would be that the case was
> sufficiently rare compared to the overall volume of data, to not be an
> issue. Oddly enough this big hammer has worked in other
> implementations at least passable well
> (https://github.com/mapserver/mapserver/blob/branch-7-0/maptree.c#L261)

Ok, I see, but that's not really what I was wondering. My question is
this: SP-GiST partitions the space into non-overlapping sections. How
can you store polygons - which can overlap - in an SP-GiST index? And
how does the compress method help with that?

- Heikki