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From: Josh Berkus <josh@agliodbs.com>
To: pgsql-performance@postgresql.org
Subject: Re: Performance issue: index not used on GROUP BY...
Date: Thu, 28 Aug 2014 13:48:05 -0700
Message-ID: <53FF9585.2020503@agliodbs.com> (raw)
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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


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