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Recommended number of virtual users
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Unregistered User Posts: 514
5/7/2012
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What is a recommended number of virtual users to simulate from one machine running an instance of StresStimulus? Is it typical to use more than one client machine for a given test? For example, if I want to simulate 500 users. It seems like the network would be a bottleneck too right? Or is that assumption incorrect? Please provide any insight or recommendations.
Thanks!
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Vadim @StresStimulus Administrator Posts: 583
5/7/2012
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Actually, there is no such magic number of VUs that is optimal in all cases. Instead, this number depends on many factors, such as capacity of your test machine(s), network bandwidth (as you correctly noted), size of your test case and server performance, just to name a few. So, the maximum number of VUs per test machine will be different in every case. For practical purposes you simply need to make sure that neither the test machine CPU, nor network creates a bottleneck.
To determine how many VUs your test machine can handle, ramp-up the virtual users until your health monitor’s light on the progress bar will start consistently turning from green to yellow or red, as it will show the machine ceiling capacity.
As far as the limit imposed by the network, make sure that the traffic generated by the test machine(s) (you can find it in the test report) does not approach the maximum available upload/download network bandwidth. Also, StresStimulus breaks down the response time on the server time and the network time. If the network time is relatively high, it also suggests that the network is a bottleneck.
In this case, consider placing the test machine (network-wise ) closer (or locally) to the server, if possible. Another alternative is to reduce the number of VUs and spread the load between several machines, accessing your server without sharing the network pipe.
As far as running the load test from multiple machines, many of our customers do that by using either physical / virtual machines from their locations, or Amazon EC2 instances. Please check these two posts:
http://www.stresstimulus.com/forum/multimachine-test-rig-235 and http://www.stresstimulus.com/forum/load-testing-from-the-cloud-231
Cheers,
-Vadim
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