Re: select max(column) from parent table very slow
От | Joshua D. Drake |
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Тема | Re: select max(column) from parent table very slow |
Дата | |
Msg-id | 44EE4DA1.5060701@commandprompt.com обсуждение исходный текст |
Ответ на | select max(column) from parent table very slow ("Sriram Dandapani" <sdandapani@counterpane.com>) |
Ответы |
Re: select max(column) from parent table very slow
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Список | pgsql-performance |
Sriram Dandapani wrote: > Parent table has a column say column1 which is indexed (parent table and > all child tables are indexed on that column) > Do you mean? select max(foo) from bar; In older versions of postgresql that would scan the whole table. In 8.1 and above it doesn't. However, I am guess that since this is a partitioned table the planner isn't smart enough to just perform the query on each child and a max on the set that is returned. Thus you are scanning each table completely. But that is just a guess. Joshua D. Drake > > > When a select max(column1) is done on parent table..takes a very long > time to get back with the result > > The same query on a child table gives instantaneous response (the tables > are quite large appx.each child table has about 20-30 million rows) > > > > Constraint exclusion is turned on. The column is not the basis for > partitioning. Postgres 8.1.2 -- === The PostgreSQL Company: Command Prompt, Inc. === Sales/Support: +1.503.667.4564 || 24x7/Emergency: +1.800.492.2240 Providing the most comprehensive PostgreSQL solutions since 1997 http://www.commandprompt.com/
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