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I have read the Gaussian Random Timer info in jmeter user manual but it is difficult to understand. any one have idea related to this please explain with example highly appreciated. Thanks in advance.
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Gaussian Random Timer element is used to delay each user request for a random period of time. It has a random deviation around the Constant Delay Offset based on Gaussian curve distribution.
You can add Constant Delay Offset and Deviation time and rest will be calculated automatically. For Constant Delay Offset of 3000 ms and Deviation time of 300 ms, each thread of JMeter would execute after {3000+(0-300 ms (could be any value between 0-300 ms)}.
The Constant Timer can be used to pause each thread for the same “think time” between requests. The above configuration will add a 5-second delay before the execution of each sampler, which is in the Constant Timer's scope. You can also use a JMeter Function or Variable in the “Thread Delay” input.
Solution : Right click on the “Thread Group” and select “Add Think Times to children” option. Jmeter will add think time after each transaction in the script.It will add a “uniform Random Timer” as a child to “Test Action” element.
I'll try to explain it with one of the examples already posted:
Approximately 68% of the delays will be between [500, 1500] ms (=[1000 - 500, 1000 + 500] ms).
According to the docs (emphasis mine):
The total delay is the sum of the Gaussian distributed value (with mean 0.0 and standard deviation 1.0) times the deviation value you specify, and the offset value
Apache JMeter invokes Random.nextGaussian()*range to calculate the delay. As explained in the Wikipedia, the value ofnextGaussian() will be between [-1,1] only for about 68% of the cases. In theory, it could have any value (though the probability to get values outside of this interval decreases very quickly with the distance to it).
As a proof, I have written a simple JMeter test that launches one thread with a dummy sampler and a Gaussian Random Timer: 3000 ms constant delay, 2000 ms deviation:
To rule out cpu load issues, I have configured an additional concurrent thread with another dummy sampler and a Constant Timer: 5000 ms:
The results are quite enlightening:
Take for instance samples 10 and 12: 9h53'04.449" - 9h52'57.776" = 6.674", that is a deviation of 3.674" in contrast to the 2.000" configured! You can also verify that the constant timer only deviates about 1ms if at all.
I could find a very nice explanation of these gaussian timers in the Gmane jmeter user's list: Timer Question.
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