Обсуждение: Strange behavior when using "limit" with example tables.
Strange behavior when using "limit" with example tables.
От
domingo@dad-it.com (Domingo Alvarez Duarte)
Дата:
In the previous post I didn't provide the tables to make the test, here I put the tables available at: http://unolotiene.com/test_tables.sql.bz2 As well I redid the test with only two tables and the problem is still there. Using "limit" makes postgresql eats all cpu for a while. Is that a bug or a mistake from my part ? ------------------------------------------------------------------------------ -- Without limit explain select ca.*, cmm.name from car_adverts as ca, car_models as cmm where ca.maker=cmm.id; NOTICE: QUERY PLAN: Merge Join (cost=2498.96..2773.64 rows=162540 width=192) -> Index Scan using car_models_pkey on car_models cmm (cost=0.00..59.00 rows=1000 width=16) -> Sort (cost=2498.96..2498.96 rows=16254 width=176) -------------------------------------------------------------------------------- -- Now with limit explain select ca.*, cmm.name from car_adverts as ca, car_models as cmm where ca.maker=cmm.id limit 10; NOTICE: QUERY PLAN: Limit (cost=0.00..32.53 rows=10 width=192) -> Nested Loop (cost=0.00..528760.54 rows=162540 width=192) -> Seq Scanon car_adverts ca (cost=0.00..505.54 rows=16254 width=176) -> Seq Scan on car_models cmm (cost=0.00..20.00 rows=1000 width=16) -> Seq Scan on car_adverts ca (cost=0.00..505.54 rows=16254 width=176)