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Help with an interesting Postgres question: Why isn't an Index Only Scan used on a partition accessed via the parent table?.
CREATE TABLE data(
id SERIAL PRIMARY KEY,
lon float,
lat float);
INSERT INTO data (lon,lat)
SELECT random() * 50 + 1,random() * 80 + 1 FROM generate_series(1,100000);
ALTER TABLE data ADD COLUMN geog geography (point,4326);
UPDATE data SET geog = ST_MakePoint(lon,lat);
CREATE INDEX idx_data_point ON data USING gist (geog) ;
CREATE TABLE
INSERT 0 100000
ALTER TABLE
UPDATE 100000
CREATE INDEX
EXPLAIN ANALYSE
SELECT ST_Distance(geog,ST_MakePoint(49.9 ,6.7)::geography,true)
FROM data
WHERE ST_DWithin(geog,ST_MakePoint(49.9,6.7),10000,true);
| QUERY PLAN |
|---|
| Index Scan using idx_data_point on data (cost=0.41..544.58 rows=10 width=8) (actual time=0.218..0.219 rows=0 loops=1) |
| Index Cond: (geog && _st_expand('0101000020E61000003333333333F34840CDCCCCCCCCCC1A40'::geography, '10000'::double precision)) |
| Filter: st_dwithin(geog, '0101000020E61000003333333333F34840CDCCCCCCCCCC1A40'::geography, '10000'::double precision, true) |
| Planning Time: 1.591 ms |
| Execution Time: 0.606 ms |
EXPLAIN