[postgis-users] ST_Overlaps and performance
Bob.Basques at ci.stpaul.mn.us
Wed Mar 7 09:36:50 PST 2012
If the polygons are always going to be level (as indicated below) and non-rotated, you might be better off just using a regular Tabular select (and non-spatial geom) and use the minx,miny,max,may numbers directly.
if (x > minx && x < max && y > miny && y < maxy) then true. . . .
Maybe build a view of the bounding corners as numeric columns and try some simple queries to test. . . . Sometimes the spatial stuff is just that much overhead for certain queries.
>>> DrYSG <ygutfreund at draper.com> wrote:
I have a table with 21 Million Rows. The Geometry field is a simple
rectangular bounding box (Polygon with 4 corners).
Users will be doing executing queries to find all overlapping rows to a user
supplied rectangle. I have been finding that my naive query of:
FROM portal.metadata as cat
41.5384615,-72.5283019 41.5384615,-72.5283019 41.1538462,-70.9433962
41.1538462,-70.9433962 41.5384615))', 4326));
Can take up to 40 seconds on a cold location. However, an ST_Contains query
of a point is only about 8 seconds. Yes, location is indexed using GIST.
CREATE INDEX catalog_location_idx
Now, it first stuck me as odd that it was taking more than 4 times the point
query to discover overlap. Then I thought about it, and I can see cases
where there ST_Overlaps cannot assume certain geometries.
I am now considering doing a WHERE clause that checks for ST_Contains for
both the Top-Left and Bottom-Right corners of the QueryRectangle since I
know that all bboxes in the DB are rectangular.
But I thought I would see what those with knowledge of the internals of the
spatial functions have to say.
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