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From "Martin Gainty" <mgai...@hotmail.com>
Subject Re: CPU usage and response time
Date Mon, 14 Aug 2006 12:34:58 GMT
Peter 
Horizontal scaling specifically Clustered solutions will address the need--

"Vertical scaling is achieved by increasing the number of servers running on a single machine,
whereas horizontal scaling is done by increasing the number of machines in the cluster
Horizontal scaling is more reliable than vertical scaling, since there are multiple machines
involved in the cluster environment, as compared to only one machine. With vertical scaling,
the machine's processing power, CPU usage, and JVM heap memory configurations are the main
factors in deciding how many server instances should be run on one machine (also known as
the server-to-CPU ratio)."

Info courtesy of
http://www.onjava.com/pub/a/onjava/2004/03/31/clustering.html

HTH
Martin --

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----- Original Message ----- 
From: "Peter Crowther" <Peter.Crowther@melandra.com>
To: "Tomcat Users List" <users@tomcat.apache.org>
Sent: Monday, August 14, 2006 3:57 AM
Subject: RE: CPU usage and response time


> From: Eickvonder Bjoern [mailto:Eickvonder.Bjoern@inside-online.de] 
> Is the following formula correct?
> 
> (response time if 100% CPU would have been granted for the request) /
> (percentage of CPU actually granted) = response time

No.  If CPU was the only resource, and thread switches were free, then
this would be close.  However, thread switches take time (which means
less time for processing servlet code) and there are other resources
that influence almost all response times - database, memory, disk and so
on.

> And second what parameters do actually influence the percentage of CPU
> that is actually granted for a request and can I adjust them?

How much time the OS allocates to Tomcat's threads.  On most OSs, Tomcat
threads map to native threads so the OS schedules each thread.
Depending on the OS, you *might* be able to reach in and adjust thread
priorities, but I wouldn't recommend it as a general solution.

What are you trying to achieve?  Tuning the application so that some
requests get relatively more CPU than others?

- Peter

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