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Re: bad estimates

From: Ken Geis <kgeis(at)speakeasy(dot)org>
To: Bruno Wolff III <bruno(at)wolff(dot)to>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: bad estimates
Date: 2003-08-29 08:10:06
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-performance
Ken Geis wrote:
> I went through the code (7.4 beta2) that estimates the cost of an index 
> scan path.  What I need to be sure of is that when running a query in 
> pgsql that uses only the columns that are in an index, the underlying 
> table need not be accessed.  I know that Oracle does this.

Thinking about it some more, it's obvious to me that a pgsql index scan 
must be accessing the underlying table even though all of the 
information needed is in the index itself.  A linear scan of a 660M file 
should not take 55 minutes.  I could confirm this with stats, but 
someone out there probably already knows the answer here.


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