Sun Java System High Availability Session Store (HADB) provides a data store that can be used to make application data available even in the case of failure. This capability is especially important for restoring state information associated with a client session. Without this capability, failure during a session requires that all operations be repeated when a the session is re-established.
The following Java ES components provide services that store session state information: Application Server, Access Manager, and Message Queue. However, Application Server is the only one of these components that can use HADB services to maintain session state during failure.
The Java ES installer provides HADB as a single installable component. However, a server and a client subcomponent are both required to provide HADB services.