# [httperf] Flag --period with option 'e'

Arlitt, Martin martin.arlitt at hp.com
Wed Nov 18 09:09:27 PST 2009

```Hi Ricardo

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httperf implements the exponential distribution, which describes the lengths of inter-arrival times in a homogeneous Poisson process.  You provided the formula for a Poisson distribution which is not used in httperf.  According to https://en.wikipedia.org/wiki/Poisson_distribtion, “if the number of arrivals in a given time interval [0,t] follows the Poisson distribution with mean lambda*t, then the lengths of the inter-arrival times follow the exponential distribution with mean 1/lambda.

Perhaps the terse description in the httperf man page was the source of your confusion.

Martin

________________________________
From: httperf-bounces at napali.hpl.hp.com [mailto:httperf-bounces at napali.hpl.hp.com] On Behalf Of ricardo figueiredo
Sent: Monday, November 16, 2009 8:42 AM
To: httperf at napali.hpl.hp.com
Subject: [httperf] Flag --period with option 'e'

Hi,

I have a doubt about --period=e
The Poisson's formula is this.
*         e is the base of the natural logarithm (e = 2.71828...)
*         k is the number of occurrences of an event - the probability of which is given by the function
*         k! is the factorial of k
*         λ is a positive real number, equal to the expected number of occurrences that occur during the given interval. For instance, if the events occur on average 4 times per minute, and you are interested in the number of events occurring in a 10 minute interval, you would use as your model a Poisson distribution with λ = 10×4 = 40.

I would like to know which value is used to constant K ???

For example,

#httperf --server www --period e0.1

e0.1 means value of lambda.

What K's value ???
--
Thank you

Ricardo
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