In a distributed environment, you can save sessions in a database using database session persistence or you can store sessions in multiple WebSphere Application Server instances using memory-to-memory session replication. WebSphere Application Server provides the following session mechanisms in a distributed environment:
When a session contains attributes that implement HttpSessionActivationListener,
notification occurs anytime the session is activated (that is, session is
read to the memory cache) or passivated (that is, session leaves the memory
cache). Passivation can occur because of a server shutdown or when the session
memory cache is full and an older session is removed from the memory cache
to make room for a newer session. It is not guaranteed that a session is passivated
in one application server prior to activation in another application.