[postgis-users] Geospatial index is not used

[Daniel, de la Cuesta Navarrete]

Hi,

I have a table with a geometry column and around 3000 rows.

The table has a geospatial index in the geometry column (service_area):

CREATE INDEX regions_index ON regions USING GIST ( service_area );

I am doing the following query:

SELECT "regions".* FROM "regions" WHERE (regions.service_area &&
ST_GeographyFromText('SRID=4326;POINT(7.04756999999995 51.17042)')) ORDER
BY admin_area_level DESC, fare_quality DESC, is_operation_region DESC LIMIT
1

It is taking around 8-9 seconds to perform this query but the problem is
that it is not taking the geospatial index, if a do EXPLAIN of the query I
get:


Limit  (cost=138.23..138.24 rows=1 width=130769)
  ->  Sort  (cost=138.23..138.24 rows=1 width=130769)

        Sort Key: admin_area_level, fare_quality, is_operation_region
        ->  Seq Scan on regions  (cost=0.00..138.22 rows=1 width=130769)

              Filter: ((service_area)::geography &&
'0101000020E6100000FF14A930B6301C40CB4A9352D0954940'::geography)

Is it possible to improve the performance of this query? Why is not taking
the geospatial index?


PostgreSQL 9.1.4 on i686-pc-linux-gnu, compiled by gcc (Ubuntu
4.4.3-4ubuntu5.1) 4.4.3, 32-bit POSTGIS=\"1.5.3\" GEOS=\"3.3.1-CAPI-1.7.1\"
PROJ=\"Rel. 4.7.1, 23 September 2009\" LIBXML=\"2.7.6\" USE_STATS"

Best
D
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