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See also JMeter best practices: http://jakartajmeter.apache.org/jmeter/usermanual/best-practices.html#lean_mean
Also, note that JMeter can place a much higher load on a system than a human user can, as it can make requests much faster. Suppose an average user waits 10 seconds between clicking links. With a wait time of 1 second, JMeter could generate 10 times the load.
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