Re: compress method for spgist - 2

From: Heikki Linnakangas <hlinnaka(at)iki(dot)fi>
To: Paul Ramsey <pramsey(at)cleverelephant(dot)ca>
Cc: Teodor Sigaev <teodor(at)sigaev(dot)ru>, Pgsql Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: compress method for spgist - 2
Date: 2015-07-23 07:36:04
Message-ID: 55B09964.80707@iki.fi
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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

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