[postgis-users] Query performance really slow..

[Pietro Rossin]

Hi all
I'm trying to query 2 vector layers;
b) bacini_elementari that is river basins - 327 elements
b) particellepac2006 colture parcels - 614000 elements

I want to intersect these two layers and get the sum of the area of each
kind of colture for each river basin.
To reduce the number of colture vectorial features I made a collect query
(grouping by kind of colture) and I made a intersection between this
geometry aggregation and all 327 basins.

My query is:

SELECT sum(st_area(ST_Intersection(bacini.geom,colture.geom))) as
areacoltura, codice_bac, nome, codice_cor, colture.descrizione
  FROM idrologia.bacini_elementari as bacini,
  (SELECT st_collect(geom) as geom, descrizione
  FROM varie.particellepac2006
  group by 2) as colture
  group by 2,3,4,5

it's 5000000ms that the query is running and I don't have any result yet...

The two geometry column have an index (but I think it's not used in this
query)

Mi pc id dual opteron with 4Gb RAM,
"PostgreSQL 9.1.3, compiled by Visual C++ build 1500, 32-bit"

"POSTGIS="2.0.0 r9605" GEOS="3.3.3-CAPI-1.7.4" PROJ="Rel. 4.8.0, 6 March
2012" GDAL="GDAL 1.9.0, released 2011/12/29" LIBXML="2.7.8"
LIBJSON="UNKNOWN" TOPOLOGY RASTER"



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