[postgis-users] speeding up simple pt-in-poly lookups

[Puneet Kishor]

This is probably a really basic question... my ST_Within or ST_Intersects selecting points in a continent are way too slow (both take upward of 200 secs).

	SELECT Count(c_id) 
	FROM c, continents n
	WHERE ST_Intersects(c.the_geom, n.the_geom) AND 
    		n.continent = 'North America';


Both tables have gist indexes on the geometries. The above query has the following plan

"Aggregate  (cost=9.66..9.67 rows=1 width=4)"
"  ->  Nested Loop  (cost=0.00..9.66 rows=1 width=4)"
"        Join Filter: _st_intersects(c.the_geom, n.the_geom)"
"        ->  Seq Scan on continents n  (cost=0.00..1.10 rows=1 width=32)"
"              Filter: ((continent)::text = 'North America'::text)"
"        ->  Index Scan using pbdb__collections_the_geom on collections c  (cost=0.00..8.30 rows=1 width=104)"
"              Index Cond: (c.the_geom && n.the_geom)"

The table c has approx 120K rows, and the continents table has 8 rows.Suggestions on how I can improve this? Yes, the computer is otherwise very swift and modern.



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Puneet Kishor