putting the equality condition on the first column of the index can make it faster.
Else, analyze, increase your stats, etc...
On Mon, 16 May 2005 13:39:40 +0200, Ilya A. Kovalenko <[EMAIL PROTECTED]> wrote:
Greetings,
How can I control which indexes will or won't be used by query ?
I never think, that I'll need something like this.
Short version:
Simple SELECT query perfomance speeds up (10x-20x) after _removing_ one of indexes. Because (as EXPLAIN shows), after removing, query switches to another index. How to make such without index removing ?
PostgreSQL 8.0.2, OpenBSD 3.7, i386 Thank you. Ilya A. Kovalenko Special EQ SW section JSC Oganer-Service
Details:
CREATE TABLE traffic_stat ( time timestamptz NOT NULL, client inet NOT NULL, remote inet NOT NULL, count_in int8 NOT NULL, count_out int8 NOT NULL ) WITHOUT OIDS;
CREATE INDEX traffic_client_idx ON traffic_stat USING btree (client); CREATE INDEX traffic_date_idx ON traffic_stat USING btree ("time"); CREATE INDEX traffic_remote_idx ON traffic_stat USING btree (remote); CREATE INDEX traffic_multy_idx ON traffic_stat USING btree ("time", client, remote); CREATE INDEX traffic_date_client_idx ON traffic_stat USING btree ("time", client);
SELECT count(*) FROM traffic_stat;
135511
Query is:
SELECT to_char(time, 'DD.MM.YYYY HH24:MI.SS'), remote, count_in, count_out
FROM traffic_stat WHERE client = '192.168.xxx.xxx' AND
time > '2005-05-16' AND time < '2005-05-16'::date + '1 days'::interval
ORDER BY time;
Case 1: SELECT ...
Total query runtime: 2643 ms. Data retrieval runtime: 20 ms. 39 rows retrieved.
EXPLAIN SELECT ...
Index Scan using traffic_date_idx on traffic_stat (cost=0.00..3.08 rows=1 width=35)
Index Cond: (("time" > '2005-05-16 00:00:00+08'::timestamp with time zone) AND ("time" < '2005-05-17 00:00:00'::timestamp without time zone))
Filter: (client = '192.168.114.31'::inet)
Case 2:
DROP INDEX traffic_date_idx;
SELECT ...
Total query runtime: 290 ms. Data retrieval runtime: 20 ms. 41 rows retrieved.
EXPLAIN SELECT ...
Index Scan using traffic_date_client_idx on traffic_stat (cost=0.00..4.37 rows=1 width=35)
Index Cond: (("time" > '2005-05-16 00:00:00+08'::timestamp with time zone) AND ("time" < '2005-05-17 00:00:00'::timestamp without time zone) AND (client = '192.168.114.31'::inet))
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