Q1- These are the 2 terms which often used for Performance Testing of an application. Simultaneous users are the users who have a valid session in the server. Each of the users would perform different actions like one doing one action, other doing another action. where as, concurrent users are the users who have a valid session in the server & they will perform the same operation at any point of time. All the concurrent users would perform different actions at the same point of time. simultaneous users have active connections to the same Web site, whereas concurrent users hit the site at exactly the same moment. Concurrent access is likely to occur at infrequent intervals. Your appliation may have 100 to 150 concurrent users but 1,000 to 1,500 simultaneous users. When load testing your application, you can simulate simultaneous users by including a random think time in your script such that not all the user threads from the load generators will request at the same moment. This is useful to simulate real world situations. However, if you want to stress your application, you probably want to use concurrent users. You can simulate concurrent users by standardizing the think time in your script to acheive estimted load. Simultaneous users: In this case, every user will wait for the other user to complete the entire transaction before executing any transaction. Simply, one after another. Concurrent users: There are 3 different levels of concurrency. 1. Application level 2. Business process level 3. Transaction level Bottom line- from the overall concept when we say 10 concurrent users, 10 users are currently active on the system at that point of time. When we say 10 simultaneous users which is not the case.
