Re: Speeding up aggregates

On Fri, 2002-12-06 at 14:46, Tom Lane wrote:
> "Josh Berkus" <josh(at)agliodbs(dot)com> writes:
> > What have other Postgres users done to speed up aggregates on large
> > tables?
>
> FWIW, I've implemented hashed aggregation in CVS tip. I have not had
> the time to try to benchmark it, but I'd be interested if anyone can
> run some tests on 7.4devel. Eliminating the need for a SORT step
> should help aggregations over large datasets.
>
> Note that even though there's no SORT, the sort_mem setting is used
> to determine the allowable hashtable size, so a too-small sort_mem
> might discourage the planner from selecting hashed aggregation.
> Use EXPLAIN to see which query plan gets chosen.

Hi.

What exactly is "hashed aggregation"?

>From Josh Berkus' email with the EXPLAIN data, it still looks like
supporting indexes aren't used, so are you still scanning the table?

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