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 a session state. Both HTTP sessions and stateful session beans (SFSBs) have session state data.
While the session state is not as important as the transactional state stored in a database, preserving the session state across server failures can be important to end users.The Application Server provides the capability to save, or persist, this session state in a repository. If the application server instance that is hosting the user session experiences a failure, the session state can be recovered. The session can continue without loss of information.
The Application Server supports the following types of session persistence stores:
High availability (HA)
With memory persistence, the state is always kept in memory and does not survive failure. With HA persistence, the Application Server uses HADB as the persistence store for both HTTP and SFSB sessions. With file persistence, the Application Server serializes session objects and stores them to the file system location specified by session manager properties. For SFSBs, if HA is not specified, the Application Server stores state information in the session-store sub-directory of this location.
Checking an SFSB’s state for changes that need to be saved is called checkpointing. When enabled, checkpointing generally occurs after any transaction involving the SFSB is completed, even if the transaction rolls back. For more information on developing stateful session beans, see Using Session Beans in Sun Java System Application Server 9.1 Developer’s Guide. For more information on enabling SFSB failover, see Stateful Session Bean Failover in Sun Java System Application Server 9.1 High Availability Administration Guide.
Apart from the number of requests being served by the Application Server, the session persistence configuration settings also affect the number of requests received per minute by the HADB, as well as the session information in each request.
For more information on configuring session persistence, see Chapter 8, Configuring High Availability Session Persistence and Failover, in Sun Java System Application Server 9.1 High Availability Administration Guide.