Re: Speeding up Aggregates

On Fri, Oct 03, 2003 at 05:44:49PM -0400, Rod Taylor wrote:
> > item_max_date() looks like this:
> > select max(dtstamp) from items where channel = $1 and link = $2;
>
> It is too bad the (channel, link) index doesn't have dtstamp at the end
> of it, otherwise the below query would be a gain (might be a small one
> anyway).
>
> select dtstamp
> from items
> where channel = $1
> and link = $2
> ORDER BY dtstamp DESC
> LIMIT 1;

Similar idea to what Josh suggested. I did create an additional index
with dtstamp at the end and it doesn't look like the planner used it.
Using the above query instead of max() didn't improve things either.

>
>
> Could you show us the exact specification of the function? In
> particular, did you mark it VOLATILE, IMMUTABLE, or STABLE?
>
> I hope it isn't the first or second one ;)

CREATE or REPLACE FUNCTION item_max_date (int4, varchar) RETURNS
timestamptz AS '
select max(dtstamp) from items where channel = $1 and link = $2;
' LANGUAGE 'sql';

--
Dror Matalon
Zapatec Inc
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Berkeley, CA 94709
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