Hello,

I didn't know where to ask this question, so i decided to ask here..

I just read yesterday the following page, look at the the USL

(Universal Law of Computational Scalability) of Dr. Gunther,

he wrote this: ( see http://en.wikipedia.org/wiki/Neil_J._Gunther)

--------------------------

The relative capacity C(N) of a computational platform is given by:

C(N) = N

-------------------

1 + (N - 1) + N (N - 1)

where N represents either the number of physical processors

in the hardware configuration or the number of users driving the

software application. The parameters and represent respectively

the levels of contention (e.g., queueing for shared resources) and

coherency delay (i.e., latency for data to become consistent) in the

system. The parameter also quantifies the retrograde throughput seen

in many stress tests but not accounted for in either Amdahl's law or

event-based simulations.

---------------

His website: http://www.perfdynamics.com/

If you read carefully , you will see that Dr. Gunther is using this

model to predict scalability after he simulates a relatively small

number

of vusers in LoadRunner ( because of licensing costs, it's cost-

effectiveness)

and after that he finds the coefficients of the 2nd-degree polynomial

(quadratic equation) and then transform those coefficients back to the

USL parameters using the = b - a and = a.

And than he is extrapolating with the USL model to higher loads

to predict scalability.

He is also applying the model to webservers with heterogeneous

workloads. like in the following page:

http://perfdynamics.blogspot.com/2009/04/assessing-usl-scalability-wi...

Now my question follows:

Suppose we have obtained a small number of measured load-points

with Loadrunner or others tools, and we calculated the USL equation to

predict scalability of a webserver , how the USL model can predict if

the scalability/performance is limited by the network bandwidth and

not the server ?

Can it give this information ?

Regards,

Amine Moulay Ramdane.

http://pages.videotron.com/aminer/