Andreas, I don't see anything glaringly wrong with your query, but hard to tell without seeing an explain plan or what you mean by takes a lot of time. Is a lot of time minutes, hours, days? How many records are we talking about here? What's the max number of points you have in any geometry. Often times its just one huge mega geometry with a 100,000 points or more slowing everything down. Do you have indexes on your year fields and date columns? Hope that helps, Regina http://www.postgis.us
_____ From: [email protected] [mailto:[email protected]] On Behalf Of Andreas Forø Tollefsen Sent: Tuesday, March 08, 2011 4:15 AM To: PostGIS Users Discussion Subject: [postgis-users] Increase query performance Hi all, Another question on postgis query performance. I did some discussion on the pgsql performance list on how i could increase the performance on my server. I did manage to increase the transactions per second, but came to the conclusion that this did not help the ST_Intersection query which i was trying to speed up. Any suggestions on how to speed up this query? Basically i want to create an intersection between a vector grid and country shapefiles. Then calculate the area of all the polygons in the intersected table, and finally selecting the country code for each cell which represents the largest area within each cell. I does work as it is, but i would like to increase the speed. The query which takes a lot of time is the ST_Intersection. "PostgreSQL 8.4.7 on i686-pc-linux-gnu, compiled by GCC gcc-4.4.real (Ubuntu/Linaro 4.4.4-14ubuntu5) 4.4.5, 32-bit" "POSTGIS="2.0.0SVN" GEOS="3.2.2-CAPI-1.6.2" PROJ="Rel. 4.7.1, 23 September 2009" LIBXML="2.7.7" USE_STATS" DROP TABLE IF EXISTS cshapesgrid1946; SELECT ST_Intersection(priogrid_land.cell, cshapeswdate.geom) AS geom, priogrid_land.gid AS divider, gwcode, gwsyear, gweyear, startdate, enddate, capname, caplong, caplat, col, row, xcoord, ycoord INTO cshapesgrid1946 FROM priogrid_land, cshapeswdate WHERE ST_Intersects(priogrid_land.cell, cshapeswdate.geom) AND cshapeswdate.gwsyear <=1946 AND cshapeswdate.gweyear >=1946 AND cshapeswdate.startdate <= '1946/1/1'; ALTER TABLE cshapesgrid1946 ADD COLUMN area float; UPDATE cshapesgrid1946 SET area = ST_Area(cshapesgrid1946.geom); DROP TABLE IF EXISTS pg1946; SELECT * INTO pg1946 FROM cshapesgrid1946 a WHERE a.area IN (SELECT MAX(area) FROM cshapesgrid1946 b GROUP BY divider); CREATE INDEX idx_pg1946 ON pg1946 USING gist(geom); Best, Andreas
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