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Re: Why so much time difference with a same query/plan?

From: Karl Vogel <karl(dot)vogel(at)telenet(dot)be>
To: Yann Michel <yann-postgresql(at)spline(dot)de>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: Why so much time difference with a same query/plan?
Date: 2004-12-26 12:30:15
Message-ID: m3y8flkzs8.fsf@telenet.be (view raw or flat)
Thread:
Lists: pgsql-performance
Yann Michel <yann-postgresql(at)spline(dot)de> writes:

> On Wed, Dec 22, 2004 at 01:52:40PM -0800, Litao Wu wrote:
>> Does the order of columns in the index matter since
>> more than 50% customer_id = 158?
>> 
>> I think it does not in Oracle.
>> 
>> Will the performance be better if I change index
>> xxx_idx to ("domain", customer_id, created)?
>
> Well, in Oracle this would of cause matter. Oracle calculates index
> usage by being able to fill all index's attributes from the left to the
> right. If any one attribute within is missing Oracle would not test if
> it is only one attribute missing, or if all other attributes are missing
> within the query's where clause. 

This depends on the version of Oracle you're using. Oracle 9i 
introduced Index Skip Scans:

 http://www.oracle.com/technology//products/oracle9i/daily/apr22.html

I don't know whether pg has something similar?

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