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Say your Web Application is spread across multiple physical servers (or may be on the same server, but using different JVMs which is of course a rarity) which might have been done to balance the load of your application OR may be the requirement is such that separate physical servers is a need than a luxury. Whatever be the case, in such a scenario if a user say log into one of the machines (JVMs to be specific) and then s/he is taken to some other Servlet/JSP running on some other server (JVM) to fulfill the client request. Now if that Servlet/JSP also requires authentication (which it would in most of the practical scenarios) then the user would be prompted to enter his/her credentials once again which s/he would of course not like. It’s the applications responsibility to transfer the credentials from one server (JVM) to another)… right?

Using Persistent Sessions, we can easily achieve a solution to this complex problem. This approach requires the session to be saved in a data source which can easily be accessed by any of the scattered servers (JVMs) and the client gets a feeling that his application is virtually running on a single server (JVM). It’s a better practice to have a completely separate data Source just for the purpose of session persistence and not to integrate session data with the application data source(s) for the obvious reason of making the overall implementation loosely coupled and hence better maintainable and more scalable.