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I am analyzing a web application and want to predict the maximum users that application can support. Now i have the below numbers out of my load test execution 1. Response Time 2. Throughput 3. CPU

I have the application use case SLA Response Time - 4 Secs CPU - 65%

When i execute load test of 10 concurrent users (without Think Time) for a particular use case the average response time reaches 3.5 Seconds and CPU touches 50%. Next I execute load test of 20 concurrent users and response time reaches 6 seconds and CPU 70% thus surpassing the SLA.

The application server configuration is 4 core 7 GB RAM.

Going by the data does this suggests that the web application can support only 10 user at a time? Is there any formula or procedure which can suggest what is the maximum users the application can support.

TIA

user3045254
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1 Answers1

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"Concurrent users" is not a meaningful measurement, unless you also model "think time" and a couple of other things.

Think about the case of people reading books on a Kindle. An average reader will turn the page every 60 seconds, sending a little ping to a central server. If the system can support 10,000 of those pings per second, how many "concurrent users" is that? About 10,000 * 60, or 600,000. Now imagine that people read faster, turning pages every 30 seconds. The same system will only be able to support half as many "concurrent users". Now imagine a game like Halo online. Each user will be emitting multiple transactions / requests per second. In other words, user behavior matters a lot, and you can't control it. You can only model it.

So, for your application, you have to make a reasonable guess at the "think time" between requests, and add that to your benchmark. Only then will you start to approach a reasonable simulation. Other things to think about are session time, variability, time of day, etc.

Chapter 4 of the "Mature Optimization Handbook" discusses a lot of these issues: http://carlos.bueno.org/optimization/mature-optimization.pdf

Carlos Bueno
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