Wrong plan or what ?
От | Mendola Gaetano |
---|---|
Тема | Wrong plan or what ? |
Дата | |
Msg-id | 00c101c35074$1e5f5b20$152aa8c0@GMENDOLA2 обсуждение исходный текст |
Ответы |
Re: Wrong plan or what ?
Re: Wrong plan or what ? |
Список | pgsql-performance |
Hi all, I'm running Postgres7.3.3 and I'm performing this simple select: select * from user_logs ul, user_data ud, class_default cd where ul.id_user = ud.id_user and ud.id_class = cd.id_class and cd.id_provider = 39; these are the number of rows for each table: user_logs: 1258955 class_default: 31 ( only one with id_provider = 39 ) user_data: 10274; this is the explain analyze for that query: QUERY PLAN Hash Join (cost=265.64..32000.76 rows=40612 width=263) (actual time=11074.21..11134.28 rows=10 loops=1) Hash Cond: ("outer".id_user = "inner".id_user) -> Seq Scan on user_logs ul (cost=0.00..24932.65 rows=1258965 width=48) (actual time=0.02..8530.21 rows=1258966 loops=1) -> Hash (cost=264.81..264.81 rows=331 width=215) (actual time=30.22..30.22 rows=0 loops=1) -> Nested Loop (cost=0.00..264.81 rows=331 width=215) (actual time=29.95..30.20 rows=6 loops=1) -> Seq Scan on class_default cd (cost=0.00..1.39 rows=1 width=55) (actual time=0.08..0.10 rows=1 loops=1) Filter: (id_provider = 39) -> Index Scan using idx_user_data_class on user_data ud (cost=0.00..258.49 rows=395 width=160) (actual time=29.82..29.96 rows=6 loops=1) Index Cond: (ud.id_class = "outer".id_class) Total runtime: 11135.65 msec (10 rows) I'm able to performe that select with these 3 steps: SELECT id_class from class_default where id_provider = 39; id_class ---------- 48 (1 row) SELECT id_user from user_data where id_class in ( 48 ); id_user --------- 10943 10942 10934 10927 10910 10909 (6 rows) SELECT * from user_logs where id_user in ( 10943, 10942, 10934, 10927, 10910, 10909 ); [SNIPPED] and the time ammount is a couple of milliseconds. Why the planner or the executor ( I don't know ) do not follow the same strategy ? Thank you Gaetano Mendola
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