J2EE applications typically have significant amounts of session state data. A web shopping cart is the classic example of a session state. Also, an application can cache frequently-needed data in the session object. In fact, almost all applications with significant user interactions need to maintain session state. Both HTTP sessions and stateful session beans (SFSBs) have session state data.
Preserving session state across server failures can be important to end users. For high availability, the Application Server provides the capability to persist session state in the HADB. If the application server instance hosting the user session experiences a failure, the session state can be recovered, and the session can continue without loss of information.
For a detailed description of how to set up high availability session persistence, see Chapter 8, Configuring High Availability Session Persistence and Failover