Users interact with an application through a client, such as a web browser or Java program. Based on the user’s actions, the client periodically sends requests to the Application Server. A user is considered active as long as the user’s session has neither expired nor been terminated. When estimating the number of concurrent users, include all active users.
The following figure illustrates a typical graph of requests processed per minute (throughput) versus number of users. Initially, as the number of users increases, throughput increases correspondingly. However, as the number of concurrent requests increases, server performance begins to saturate, and throughput begins to decline.
Identify the point at which adding concurrent users reduces the number of requests that can be processed per minute. This point indicates when optimal performance is reached and beyond which throughput start to degrade. Generally, strive to operate the system at optimal throughput as much as possible. You might need to add processing power to handle additional load and increase throughput.