Re: Unused index influencing sequential scan plan

From: Peter Geoghegan <peter(at)2ndquadrant(dot)com>
To: Thom Brown <thom(at)linux(dot)com>
Cc: pgsql-performance <pgsql-performance(at)postgresql(dot)org>
Subject: Re: Unused index influencing sequential scan plan
Date: 2012-10-18 16:24:42
Message-ID: CAEYLb_XP7UEPdCwypJi97dcvgdpSBzoK0Rym1nmTp1Z5TtegFg@mail.gmail.com
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On 18 October 2012 17:11, Thom Brown <thom(at)linux(dot)com> wrote:
> The estimate is down to almost a 10th of what it was before. What's going on?

Even though the index isn't used, the pg_statistic entries that the
expression index would have made available are. It's as if you
materialised the expression into a column, analyzed and grouped by
that.

--
Peter Geoghegan http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training and Services

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