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postgresqlindexingpostgis

Postgresql gist index ignored for st_dwithin

I have a database of points (10 million) in postgresql 12 which has the postgis extension. I have created a gist index on the points column and I need to filter the points based on distance from a given point. It seems that the index is not used. I run the following explain:

EXPLAIN
SELECT actual_location
FROM geometries
WHERE ST_DWithin(ST_SetSRID(ST_MakePoint(30,30), 4326), actual_location, 100000, true);

which yields:

enter image description here


so it seems it only does a parallel seq scan. Am I getting something wrong here? Should I be using a different index type? When the database was populated with 1 million points, it returned results in about 1.3 seconds. With 10 million it goes to about 11-13 which is not acceptable for a user of my application to wait that much time.

Solution

  • Turns out I should have created the index like so:

    CREATE INDEX example_idx ON geometries USING GIST (geography(actual_location));