From: Tom Lane <tgl@sss.pgh.pa.us>
To: marko@joh.to
cc: pgsql-bugs@postgresql.org
Subject: Re: BUG #11500: PRIMARY KEY index not being used
In-reply-to: <20140926080211.7639.68358@wrigleys.postgresql.org>
References: <20140926080211.7639.68358@wrigleys.postgresql.org>
Comments: In-reply-to marko@joh.to
 message dated "Fri, 26 Sep 2014 08:02:11 -0000"
Date: Fri, 26 Sep 2014 13:44:39 -0400
Message-ID: <8043.1411753479@sss.pgh.pa.us>
Precedence: bulk
Sender: pgsql-bugs-owner@postgresql.org

marko@joh.to writes:
> PostgreSQL version: 9.1.12

> We've been observing a performance problem where a PRIMARY KEY index is not
> being used.  The problem looks like this:

In 9.2 and again in 9.3, we significantly changed the planner's modeling
of index access costs, with a view towards making better choices when
there are multiple plausible indexes to use.  If you can reproduce this
misbehavior in 9.3 or later it would be worth looking into; but we're not
going to change 9.1's estimation rules at this late date.  People running
on back branches tend to want plan stability in my experience.

			regards, tom lane


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