Re: Optimizing sum() operations

On Fri, Oct 3, 2008 at 4:51 AM, Dobes Vandermeer <dobesv@gmail.com> wrote:
> I'm currently using sum() to compute historical values in reports;
> basically select sum(amount) on records where date <= '...' and date
>>= '...' who = X.
>
> Of course, I have an index on the table for who and date, but that
> still leaves potentially thousands of rows to scan.
>
> First, should I be worried about the performance of this, or will
> postgres sum a few thousand rows in a few milliseconds on a decent
> system anyway?
>
> Second, if this is a concern, is there a best practice for optimizing
> these kinds of queries?

You'll need to test to see what performance you get.  That said,
indexing is a good place to start.  You can always run explain and
explain analyze on the queries to double-check the planner.

Sean