Chapter 2 GatherinG requirements When you need to determine the number of real simultaneous users that the application can support, you first need to calculate the maximum throughput. Maximum throughput is calculated by running a few emulated users with zero think time. That means each user sends a request, receives a response, and immediately loops back to send the next request. • Maximum users the application has to support: Once you have the maximum throughput, you can use Little’s Law to estimate the number of maximum concurrent users that the application can support. N = X / λ N is the number of concurrent users. λ is the average arrival rate. X is the throughput. • Maximum concurrent users: If the application has ab average interarrival time of 5 seconds, using Little’s Law we can now compute N (number of users) as: N = X /λ = 2015 * 5 = 10075 users. Your application running on the same infrastructure can support more than 10,000 concurrent users with an interarrival time of 5 seconds. • Maximum concurrent volume: You need to calculate maximum concurrent users per hour that need to be supported by the application. • After estimating the concurrent user and load supported by the DXP application on the particular infrastructure, you can decide to scale your infrastructure accordingly. • User growth rate: You need to estimate percentage increase in user traffic per year so that you are able to scale up your infrastructure in the future. 45