=?ISO-8859-1?Q?Andreas_For=F8_Tollefsen?= <andreasft@xxxxxxxxx> writes: > This is a query i am working on now. It creates an intersection of two > geometries. One is a grid of 0.5 x 0.5 decimal degree sized cells, while the > other is the country geometries of all countries in the world for a certain > year. Hm, are you sure your data is right? Because the actual rowcounts imply that each country intersects about half of the grid cells, which doesn't seem right. > priogrid=# EXPLAIN ANALYZE SELECT priogrid_land.gid, gwcode, > ST_Intersection(pri > ogrid_land.cell, cshapeswdate.geom) FROM priogrid_land, cshapeswdate WHERE > ST_Intersects(priogrid_land.cell, cshapeswdate.geom); > QUERY > PLAN > -------------------------------------------------------------------------------- > ------------------------------------------------------------------ > Nested Loop (cost=0.00..12644.85 rows=43351 width=87704) (actual > time=1.815..7 > 074973.711 rows=130331 loops=1) > Join Filter: _st_intersects(priogrid_land.cell, cshapeswdate.geom) > -> Seq Scan on cshapeswdate (cost=0.00..14.42 rows=242 width=87248) > (actual > time=0.007..0.570 rows=242 loops=1) > -> Index Scan using idx_priogrid_land_cell on priogrid_land > (cost=0.00..7.1 > 5 rows=1 width=456) (actual time=0.069..5.604 rows=978 loops=242) > Index Cond: (priogrid_land.cell && cshapeswdate.geom) > Total runtime: 7075188.549 ms > (6 rows) AFAICT, all of the runtime is going into calculating the ST_Intersects and/or ST_Intersection functions. The two scans are only accounting for perhaps 5.5 seconds, and the join infrastructure isn't going to be terribly expensive, so it's got to be those functions. Not knowing much about PostGIS, I don't know if the functions themselves can be expected to be really slow. If it's not them, it could be the cost of fetching their arguments --- in particular, I bet the country outlines are very large objects and are toasted out-of-line. There's been some past discussion of automatically avoiding repeated detoastings in scenarios like the above, but nothing's gotten to the point of acceptance yet. Possibly you could do something to force detoasting in a subquery. regards, tom lane -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
