Hi, I am relatively new to PostgreSQL(8.1) and facing the following problem.
We have indexes defined on timestamp and description (create index description_idx on event using btree (description varchar_pattern_ops)) EXPLAIN ANALYZE SELECT event_id, category, current_session_number, description, event_type_id, realm_name, root_session_number, severity, source_name, target_key, target_name, timestamp, jdo_version FROM event WHERE description like '%mismatch%' ORDER BY timestamp desc; QUERY PLAN ---------------------------------------------------------------------------------------------------------------------- Sort (cost=36267.09..36272.73 rows=2256 width=314) (actual time=19255.075..20345.774 rows=647537 loops=1) Sort Key: "timestamp" Sort Method: external merge Disk: 194080kB -> Seq Scan on event (cost=0.00..36141.44 rows=2256 width=314) (actual time=0.080..1475.041 rows=647537 loops=1) Filter: ((description)::text ~~ '%mismatch%'::text) Total runtime: 22547.292 ms (6 rows) But startsWith query use indexes. EXPLAIN ANALYZE SELECT event_id, category, current_session_number, description, event_type_id, realm_name, root_session_number, severity, source_name, target_key, target_name, timestamp, jdo_version FROM event WHERE description like 'mismatch%' ORDER BY timestamp desc; QUERY PLAN ------------------------------------------------------------------------------------------------------------------------------- Sort (cost=9.26..9.27 rows=1 width=314) (actual time=0.766..0.766 rows=0 loops=1) Sort Key: "timestamp" Sort Method: quicksort Memory: 17kB -> Index Scan using description_idx on event (cost=0.00..9.25 rows=1 width=314) (actual time=0.741..0.741 rows=0 loops=1) Index Cond: (((description)::text ~>=~ 'mismatch'::text) AND ((description)::text ~<~ 'mismatci'::text)) Filter: ((description)::text ~~ 'mismatch%'::text) Total runtime: 0.919 ms (7 rows) Is there any tweaks to force pgsql to use index on description? Balaji P.S The event database has 700k records.