From: Joshua D. Drake <jd@commandprompt.com>
To: Sriram Dandapani <sdandapani@counterpane.com>
Cc: Pgsql-Performance (E-mail) <pgsql-performance@postgresql.org>
Subject: Re: select max(column) from parent table very slow
Date: Thu, 24 Aug 2006 18:08:49 -0700
Message-ID: <44EE4DA1.5060701@commandprompt.com> (raw)
In-Reply-To: <6992E470F12A444BB787B5C937B9D4DF057500BF@ca-mail1.cis.local>
References: <6992E470F12A444BB787B5C937B9D4DF057500BF@ca-mail1.cis.local>
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
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To: pgsql-performance@postgresql.org
Cc: jd@commandprompt.com, sdandapani@counterpane.com
Subject: Re: select max(column) from parent table very slow
In-Reply-To: <44EE4DA1.5060701@commandprompt.com>
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