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<P><FONT SIZE=2>To my untutored eye it looks like the slower one is using the geometry ("index cond: (the_geom &&" vs "index cond: (bbox &&") ... a bounding box has 4 count 'em 4 points (not sure if all are even stored) while your geometry has way more than that. So the comparison of the simple is *way* faster. As it should be.<BR>
<BR>
QED ?<BR>
<BR>
Greg Williamson<BR>
Senior DBA<BR>
GlobeXplorer LLC, a DigitalGlobe company<BR>
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-----Original Message-----<BR>
From: postgis-users-bounces@postgis.refractions.net on behalf of Stefan Zweig<BR>
Sent: Fri 9/7/2007 3:36 AM<BR>
To: PostGIS Users Discussion<BR>
Subject: Re: [postgis-users] question on gist performance<BR>
<BR>
hi frank,<BR>
<BR>
this what analyze says:<BR>
<BR>
"Index Scan using mytable_the_geom_gist on mytable (cost=0.00..4.95 rows=1 width=13)"<BR>
" Index Cond: (the_geom && '0103000020E610000001000000050000000000004077852B40000000C0E69549400000004077852B40000000002FEB4940000000C0AE762E40000000002FEB4940000000C0AE762E40000000C0E69549400000004077852B40000000C0E6954940'::geometry)"<BR>
" Filter: (the_geom && '0103000020E610000001000000050000000000004077852B40000000C0E69549400000004077852B40000000002FEB4940000000C0AE762E40000000002FEB4940000000C0AE762E40000000C0E69549400000004077852B40000000C0E6954940'::geometry)"<BR>
<BR>
"Index Scan using mytable_bbox_gist on mytable (cost=0.00..4.95 rows=1 width=13)"<BR>
" Index Cond: (bbox && '0103000020E610000001000000050000000000004077852B40000000C0E69549400000004077852B40000000002FEB4940000000C0AE762E40000000002FEB4940000000C0AE762E40000000C0E69549400000004077852B40000000C0E6954940'::geometry)"<BR>
" Filter: (bbox && '0103000020E610000001000000050000000000004077852B40000000C0E69549400000004077852B40000000002FEB4940000000C0AE762E40000000002FEB4940000000C0AE762E40000000C0E69549400000004077852B40000000C0E6954940'::geometry)"<BR>
<BR>
still strange.. both querys are using the same index, but there is a dramatically difference in performance. could it be that the first query on the_geom column needs to parse the geometry(s) to gather bounding box information from them (which i actually would not have thought so)?<BR>
<BR>
kind regards, stefan<BR>
<BR>
<BR>
> -----Ursprüngliche Nachricht-----<BR>
> Von: PostGIS Users Discussion <postgis-users@postgis.refractions.net><BR>
> Gesendet: 07.09.07 10:44:16<BR>
> An: PostGIS Users Discussion <postgis-users@postgis.refractions.net><BR>
> Betreff: Re: [postgis-users] question on gist performance<BR>
<BR>
<BR>
><BR>
> Stefan,<BR>
><BR>
> * Stefan Zweig <stefanzweig1881@web.de> [070907 10:07]:<BR>
> > thanks for your quick reply. i have tried your advice and rebuilded<BR>
> > all my gist indexes on the table (via drop index, create index) and<BR>
> > run a vacuum full afterwards. but that did not change the fact, that<BR>
> > the query on the_geom is much slower than the same one on the_geom_1.<BR>
> ><BR>
> [...]<BR>
> ><BR>
> > '...WHERE the_geom && expr;' takes about 250ms,<BR>
> > '...WHERE the_geom_envelope && expr;' takes about 20ms.<BR>
> ><BR>
> > ANALYZE says that GIST is used. As far as I know, the GIST makes use<BR>
> > only of the bounding boxes of Geometry objects, which are equal for<BR>
> > each object. How does it come that the query time using the_geom is more than<BR>
> > *ten times slower* than the query time using the_geom_envelope?"<BR>
><BR>
> It would help if you post the explain analyse output.<BR>
><BR>
> Regards,<BR>
><BR>
> Frank<BR>
><BR>
> --<BR>
> Frank Koormann | ++49-541-335 08 30 | <A HREF="http://www.intevation.net/">http://www.intevation.net/</A><BR>
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