I'm using PostgreSQL 8.1.4 and I'm trying to force the planner to use an index. With the index, I get executions times of 0.5 seconds. Without, it's closer to 2.5 seconds. Compare these two sets of results (also provided at http://rafb.net/paste/results/ywcOZP66.html should it appear poorly formatted below): freshports.org=# \i test2.sql QUERY PLAN ---------------------------------------------------------------------- ---------------------------------------------------------------------- - Merge Join (cost=24030.39..24091.43 rows=3028 width=206) (actual time=301.301..355.261 rows=3149 loops=1) Merge Cond: ("outer".id = "inner".category_id) -> Sort (cost=11.17..11.41 rows=97 width=4) (actual time=0.954..1.300 rows=95 loops=1) Sort Key: c.id -> Seq Scan on categories c (cost=0.00..7.97 rows=97 width=4) (actual time=0.092..0.517 rows=97 loops=1) -> Sort (cost=24019.22..24026.79 rows=3028 width=206) (actual time=300.317..314.114 rows=3149 loops=1) Sort Key: p.category_id -> Nested Loop (cost=0.00..23844.14 rows=3028 width=206) (actual time=0.082..264.459 rows=3149 loops=1) -> Seq Scan on ports p (cost=0.00..6141.11 rows=3028 width=206) (actual time=0.026..133.575 rows=3149 loops=1) Filter: (status = 'D'::bpchar) -> Index Scan using element_pkey on element e (cost=0.00..5.83 rows=1 width=4) (actual time=0.022..0.026 rows=1 loops=3149) Index Cond: ("outer".element_id = e.id) Total runtime: 369.869 ms (13 rows) freshports.org=# set enable_hashjoin = true; SET freshports.org=# \i test2.sql QUERY PLAN ---------------------------------------------------------------------- ---------------------------------------------------------- Hash Join (cost=6156.90..13541.14 rows=3028 width=206) (actual time=154.741..2334.366 rows=3149 loops=1) Hash Cond: ("outer".category_id = "inner".id) -> Hash Join (cost=6148.68..13472.36 rows=3028 width=206) (actual time=153.801..2288.792 rows=3149 loops=1) Hash Cond: ("outer".id = "inner".element_id) -> Seq Scan on element e (cost=0.00..4766.70 rows=252670 width=4) (actual time=0.022..1062.626 rows=252670 loops=1) -> Hash (cost=6141.11..6141.11 rows=3028 width=206) (actual time=151.105..151.105 rows=3149 loops=1) -> Seq Scan on ports p (cost=0.00..6141.11 rows=3028 width=206) (actual time=0.027..131.072 rows=3149 loops=1) Filter: (status = 'D'::bpchar) -> Hash (cost=7.97..7.97 rows=97 width=4) (actual time=0.885..0.885 rows=97 loops=1) -> Seq Scan on categories c (cost=0.00..7.97 rows=97 width=4) (actual time=0.076..0.476 rows=97 loops=1) Total runtime: 2346.877 ms (11 rows) freshports.org=# Without leaving "enable_hashjoin = false", can you suggest a way to force the index usage? FYI, the query is: explain analyse SELECT P.id, P.category_id, P.version as version, P.revision as revision, P.element_id, P.maintainer, P.short_description, to_char(P.date_added - SystemTimeAdjust(), 'DD Mon YYYY HH24:MI:SS') as date_added, P.last_commit_id as last_change_log_id, P.package_exists, P.extract_suffix, P.homepage, P.status, P.broken, P.forbidden, P.ignore, P.restricted, P.deprecated, P.no_cdrom, P.expiration_date, P.latest_link FROM categories C, ports P JOIN element E on P.element_id = E.id WHERE P.status = 'D' AND P.category_id = C.id; -- Dan Langille : Software Developer looking for work my resume: http://www.freebsddiary.org/dan_langille.php
