Re: select max(column) from parent table very slow - Mailing list 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




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