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Editorial Team
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Asked: 2026-05-22T01:29:04+00:00

I am designing some system that will store records containing a begin and end

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I am designing some system that will store records containing a begin and end time. For example:

CREATE TABLE test (
  id bigserial PRIMARY KEY,
  ts_start timestamp NOT NULL,
  ts_end timestamp NOT NULL,
  foo bar NOT NULL,
  ...
);

Now I want to run queries on this to find all rows that overlap with a certain timestamp. This would result in a where clause like:

WHERE ts_start <= '2006-4-6 12:34:56' AND ts_end > '2006-4-6 12:34:56'

I did test this with a massive amount of generated test data and the performance is quite bad. I tested it with an index on ts_start and another index on ts_end and also with an multi column index on ts_start and ts_end. The last gave the best result but it is still far from optimal.

The problem is that postgresql doesn’t know the fact that ts_end is guaranteed to be larger then ts_start so it uses a plan that is capable of finding rows where ts_end is smaller then ts_start.

Any suggestions how to solve this problem?

Edit:
For people having this problem too if you can wait a little longer then PostgreSQL 9.2 has the perfect solution: range types. 9.2 is in beta now final release will most likely be at the end of 2012.

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1 Answer

  1. Editorial Team

    There was “temporal postgres” (google it) but I don’t know if it is still maintained… I believe there was a discussion of including this type of search into postgres but I don’t remember the final state of it. Anyway :

    Example using box and gist :

    CREATE TABLE segments( start INTEGER NOT NULL, stop INTEGER NOT NULL, range_box BOX NOT NULL );
INSERT INTO segments SELECT n,n+1,BOX(POINT(n,-1),POINT(n+1,1)) FROM generate_series( 1, 1000000 ) n;
CREATE INDEX segments_box ON segments USING gist( range_box );
CREATE INDEX segments_start ON segments(start);
CREATE INDEX segments_stop ON segments(stop);

EXPLAIN ANALYZE SELECT * FROM segments WHERE 300000 BETWEEN start AND stop;
 Index Scan using segments_start on segments  (cost=0.00..12959.24 rows=209597 width=72) (actual time=91.990..91.990 rows=2 loops=1)
   Index Cond: (300000 >= start)
   Filter: (300000 <= stop)
 Total runtime: 92.023 ms

EXPLAIN ANALYZE SELECT * FROM segments WHERE range_box && '(300000,0,300000,0)'::BOX;
 Bitmap Heap Scan on segments  (cost=283.49..9740.27 rows=5000 width=72) (actual time=0.036..0.037 rows=2 loops=1)
   Recheck Cond: (range_box && '(300000,0),(300000,0)'::box)
   ->  Bitmap Index Scan on segments_box  (cost=0.00..282.24 rows=5000 width=0) (actual time=0.032..0.032 rows=2 loops=1)
         Index Cond: (range_box && '(300000,0),(300000,0)'::box)
 Total runtime: 0.064 ms

    As you can see gist index is ridiculously fast here (1500 times ! lol)
    (and you can use many operators like overlaps, is contained, contains, etc.

    http://www.postgresql.org/docs/8.2/static/functions-geometry.html

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