I think your query does not use the index on net_geom because it is not a spatial index (not a gist one) on the geometry, but a btree index on the id. You should make the index (create index net_geom_gist on net_geom using gist(geom) ) and try again your query Hugues.
________________________________ De : postgis-users-boun...@postgis.refractions.net [mailto:postgis-users-boun...@postgis.refractions.net] De la part de Thomas Klemmer Envoyé : mardi 11 septembre 2012 11:09 À : postgis-users@postgis.refractions.net Objet : [postgis-users] ST_DWithin is not using SpatialIndex with Subquery Hi folks first of here some system informations: Server: Ubuntu 12.04 LTS, 16GB RAM 1TB 4x SSD HW Raid "PostgreSQL 9.1.5 on x86_64-unknown-linux-gnu, compiled by gcc (Ubuntu/Linaro 4.6.3-1ubuntu5) 4.6.3, 64-bit" "POSTGIS="2.0.0 r9605" GEOS="3.3.3-CAPI-1.7.4" PROJ="Rel. 4.7.1, 23 September 2009" GDAL="GDAL 1.9.1, released 2012/05/15" LIBXML="2.7.8" LIBJSON="UNKNOWN" TOPOLOGY RASTER" Database: TableName: PointTbl_v1 Index: idx_pdb_v1 NumRows: 4.09806e+08 TableSize: 280 GB IndexSize: 21 GB [Gist on(point_pos)] GeometryCo: point_pos Type: POINT Dimensions: 2 SRID: 4326 /----------------------------------------------- TableName: PointTbl_v5 Index: idx_pdb_v5 NumRows: 4.16218e+07 TableSize: 19 GB IndexSize: 2344 MB [Gist on(point_pos)] Primarykey: false GeometryCo: point_pos Type: POINT Dimensions: 2 SRID: 4326 /----------------------------------------------- TableName: NetTbl Index: idx_net NumRows: 270615 TableSize: 195 MB IndexSize: 17 MB Primarykey: NetTbl_pk GeometryCo: net_geom Type: LINESTRING Dimensions: 2 SRID: 4326 Basically I'm trying to gather all points from PointTbl_v5 / PointTbl_v1 that are close or on a LineString in NetTbl; Here ist the Query I'm trying to run: SELECT ST_AsBinary(point_pos) AS point_pos, oid, ..., type FROM PointTbl_v5 WHERE ST_DWithin(point_pos,(SELECT net_geom from NetTbl where ogc_fid = 500) ,5e-05); This query takes 319005 msec to return which is very slow due to the a seq scan done on PoinDB_v5 EXPLAIN ANALYSE "Seq Scan on PointTbl_v5 (cost=10000000008.36..10013364820.01 rows=13873927 width=202) (actual time=199926.978..318895.494 rows=5 loops=1)" " Filter: st_dwithin(point_pos, $0, 5e-05::double precision)" " InitPlan 1 (returns $0)" " -> Index Scan using NetTbl_pk on NetTbl (cost=0.00..8.36 rows=1 width=847) (actual time=2.069..2.075 rows=1 loops=1)" " Index Cond: (ogc_fid = 2)" "Total runtime: 318895.583 ms" The query: SELECT ST_AsText(net_geom) from NetTbl where ogc_fid = 2 returns in 16 ms; If I instert the Geometry by Hand into the first query like this: SELECT ST_AsBinary(point_pos) AS point_pos, oid, country, federalstate, district, town FROM PointTbl_v5 WHERE ST_DWithin(point_pos, ST_GeomFromText( 'LINESTRING(....)',4326),5e-05); This query return in 63ms on the small table and 766ms on the bigger table. EXPLAIN ANALYSE "Index Scan using idx_pdb_v5 on PointTbl_v5 (cost=0.00..147.61 rows=1 width=202) (actual time=0.047..1.050 rows=23 loops=1)" " Index Cond: (point_pos && '0103.....A40'::geometry)" " Filter: (('0102.....4A40'::geometry && st_expand(point_pos, 5e-05::double precision)) AND _st_dwithin(point_pos, '01020.....A40'::geometry, 5e-05::double precision))" "Total runtime: 1.080 ms" Does anybody have a clue why the first query with the subquery for the LineString Geometry withing ST_DWithin not using the Spatial index? seqscan_enabled is turned off... cheers Thomas
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