On 4/2/07, Rickard Sjöström <rickard.sjostrom@xxxxxxxxxxxxxx> wrote:
Hi! This post is related to the post "Performance of views" but this is another problem now. Problem: PostgreSQL seems to not use my index. My postgres is 7.4. I started all over again and got my query really fast on one database (~40 seconds became 150 ms). BUT when trying on another db (same postgres server but with approx. 4 times as much data) it was really slow again (say 10 seconds). Then I run the EXPLAIN ANALYSE of a sub-query of my query which I realize was the problem. It seems that it does not make use of the index in the slower database!? fast db: ------------------------- -> Index Scan using testcase_b_bid_index on testcase (cost=0.00..1656.82 rows=426 width=38) (never executed)" ------------------------- slow db: ------------------------- -> Seq Scan on testcase (cost=0.00..2896.42 rows=33242 width=64) (actual time=77.027..791.014 rows=37093 loops=1)" ------------------------- rows=37093 is all of the existing rows of table testcase! (why does it say "never executed"?)
Hi, a full index scan is even more expensive than a sequential scan. So the query optimizer works fine. Regards Federico
