From: Gregory Stark <stark@enterprisedb.com>
To: Carlo Stonebanks <stonec.register@sympatico.ca>
Cc: pgsql-performance@postgresql.org
Subject: Re: Acceptable level of over-estimation?
Date: Mon, 24 Sep 2007 21:18:25 +0100
Message-ID: <87k5qfom0e.fsf@oxford.xeocode.com> (raw)
In-Reply-To: <fd93l6$a7l$1@news.hub.org>
References: <fd93l6$a7l$1@news.hub.org>
"Carlo Stonebanks" <stonec.register@sympatico.ca> writes:
> Is there a rule of thumb about when the planner's row estimates are too high?
> In particular, when should I be concerned that planner's estimated number of
> rows estimated for a nested loop is off? By a factor of 10? 100? 1000?
Not really. It's a big enough difference for the planner to make a bad
decision or it isn't. But if you pressed me I would say a factor of 10 is bad.
A factor of 2 is inevitable in some cases.
--
Gregory Stark
EnterpriseDB http://www.enterprisedb.com
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To: pgsql-performance@postgresql.org
Cc: stark@enterprisedb.com, stonec.register@sympatico.ca
Subject: Re: Acceptable level of over-estimation?
In-Reply-To: <87k5qfom0e.fsf@oxford.xeocode.com>
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