Re: Gaussian Random Timer behavior

[sebb <se...@gmail.com>]

On 09/09/2009, Marc Chiarini <ma...@tufts.edu> wrote:
> Hi Folks,
>
>  I am trying to verify that I am looking at my "problem" from the correct
>  perspective.  I have a single thread group and a http sampler that
>  requests the same file repeatedly for some user-defined duration (say
>  300 seconds).  The sampler has a Gaussian Random Timer as a child with
>  offset and std dev set manually (e.g., 500ms offset and 50ms deviation),
>  in order to rule out any weirdness using variables.  When I run the test
>  with one thread, I obtain my desired behavior: the delay between
>  requests is normally distributed with mean and std dev very close to the
>  timer settings.  However when I use 2 or more threads, I get delay
>  distributions that are not fitting any particular distribution and are
>  certainly not normal.  As I go higher with the number of threads (and
>  correspondingly increase the offset and std dev, just to make sure the
>  center mass is sufficiently distant from zero), the distribution starts
>  to look exponential.  Am I missing something?  If it is true that the
>  sum of two or more normal distributions is itself a normal distribution,
>  then I don't understand why using multiple threads in this fashion
>  results in this behavior.
>
>  Any help is greatly appreciated.

Try using a Java Request sampler instead of the HttpSampler.

That will eliminate any network or server variations, and will prove a
useful test case in case there is a bug in JMeter.

Obviously you won't be able to test the server, but it should make
investigating the timing issues much simpler.

>  Regards,
>  Marc
>
>  PS  I reproduced the generation of normally distributed delay times
>  using a Beanshell timer, but obtain similar results.
>
>
>
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