index and queries using '<' '>'

[Marc Boucher]

I'm using PG 7.3.4

I've a table with a column of type int8 where I store date-based values,
and an index exists for it.
The problem is that the index is almost never used with the '>' test.

# explain SELECT date FROM album WHERE (date='1093989600');
Index Scan using date_album_key on album (cost=0.00..86.31 rows=21 width=8)
Index Cond: (date = 1093989600::bigint)

# explain SELECT date FROM album WHERE (date>'1093989600');
Seq Scan on album (cost=0.00..907.91 rows=447 width=8)
Filter: (date > 1093989600::bigint)

# explain SELECT date FROM album WHERE (date>'1099989600');
Index Scan using date_album_key on album (cost=0.00..323.09 rows=84 width=8)
Index Cond: (date > 1099989600::bigint)
It works when the query is supposed to generate low number of rows. The
problem is that the execution time is much longer with a scan.
How can I force the use of this index?
--
Marc
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TIP 4: Don't 'kill -9' the postmaster

[Martijn van Oosterhout]

The system seems to think that a scan is cheap because the table is so
small. Have you ever ANALYZEd that table? Also, EXPLAIN ANALYZE gives a
much better idea of what is going on...

On Thu, Nov 18, 2004 at 03:55:12PM +0100, Marc Boucher wrote:

I'm using PG 7.3.4

I've a table with a column of type int8 where I store date-based values,
and an index exists for it.
The problem is that the index is almost never used with the '>' test.

# explain SELECT date FROM album WHERE (date='1093989600');
Index Scan using date_album_key on album (cost=0.00..86.31 rows=21 width=8)
Index Cond: (date = 1093989600::bigint)

# explain SELECT date FROM album WHERE (date>'1093989600');
Seq Scan on album (cost=0.00..907.91 rows=447 width=8)
Filter: (date > 1093989600::bigint)

# explain SELECT date FROM album WHERE (date>'1099989600');
Index Scan using date_album_key on album (cost=0.00..323.09 rows=84width=8)
Index Cond: (date > 1099989600::bigint)


It works when the query is supposed to generate low number of rows. The
problem is that the execution time is much longer with a scan.
How can I force the use of this index?


--
Marc


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TIP 4: Don't 'kill -9' the postmaster
--
Martijn van Oosterhout <kl*****@svana.org> http://svana.org/kleptog/ Patent. n. Genius is 5% inspiration and 95% perspiration. A patent is a
tool for doing 5% of the work and then sitting around waiting for someone
else to do the other 95% so you can sue them.

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