Re: Performance issue: index not used on GROUP BY...

On 08/28/2014 01:50 AM, gmb wrote:
> Can somebody please confirm whether aggregate functions such as GROUP BY
> should use indexes ? 

Sometimes.  In your case, the index has one more column than the GROUP
BY, which makes it less likely that Postgres will use it (since
depending on the cardinality of ddet_id, it might actually be slower to
use the index).

In addition, other folks on this thread have already pointed out the
memory settings issues to you.

-- 
Josh Berkus
PostgreSQL Experts Inc.
http://pgexperts.com