[postgis-users] Optimizing ST_Intersection

[vinod.khare at gmail.com]

I have a table containing all roads in the US. Naturally, this table is very
large with more that 20 million rows. I want to find the intersection of
these roads with a single linestring (representing a pipeline).

SELECT ST_AsText(ST_Intersection(
    (SELECT the_geom FROM roads)
    (SELECT the_geom FROM pipes WHERE pipeid = 1)));

I have created a gist index on roads but the query planner does not use it.
The query takes a really long time. Is there some way to optimize this?

thanks,
Vinod.
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