Message-ID: <44C381CF.4050800@modgraph-usa.com>
Date: Sun, 23 Jul 2006 07:03:59 -0700
From: "Craig A. James" <cjames@modgraph-usa.com>
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To: Michael Stone <mstone+postgres@mathom.us>,
 pgsql-performance@postgresql.org
Subject: Re: Forcing using index instead of sequential scan?
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	<44C25FDD.8070003@modgraph-usa.com>
	<20060723110724.GU8069@mathom.us>
In-Reply-To: <20060723110724.GU8069@mathom.us>
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Michael Stone wrote:
> On Sat, Jul 22, 2006 at 10:26:53AM -0700, Craig A. James wrote:
>> This causes massive file-system activity and flushes all files that 
>> the kernel has cached.  If you run this between each Postgres test 
>> (let it run for a couple minutes), it gives you an apples-to-apples 
>> comparison between successive benchmarks, and eliminates the effects 
>> of caching.
> 
> Assuming a system with small ram or an unusually large system 
> installation. Unmounting is a much more realiable mechanism.

Indeed, but it only works if you can.  For example, in my small-ish installation, my WAL and system tables are mounted on the root disk.  Or someone might not have super-user access.

Craig