Java EE applications’ need for session persistence was previously described in Session Persistence. The Application Server uses the high-availability database (HADB) as a highly available session store. HADB is included with the Sun GlassFish Enterprise Server with HADB, but in deployment can be run on separate hosts. HADB provides a highly available data store for HTTP session and stateful session bean data.
The advantages of this decoupled architecture include:
Server instances in a highly available cluster are loosely coupled and act as high performance Java EE containers.
Stopping and starting server instances does not affect other servers or their availability.
HADB can run on a different set of less expensive machines (for example, with single or dual processors). Several clusters can share these machines. Depending upon the deployment needs, you can run HADB on the same machines as Application Server (co-located) or different machines (separate tier). For more information on the two options, see Co-located Topology
As state management requirements change, you can add resources to the HADB system without affecting existing clusters or their applications.
HADB is optimized for use by Application Server and is not meant to be used by applications as a general purpose database.
For HADB hardware and network system requirements, seeHardware and Software Requirements in Sun GlassFish Enterprise Server 2.1 Release Notes. For additional system configuration steps required for HADB, see Chapter 10, Installing and Setting Up High Availability Database, in Sun GlassFish Enterprise Server 2.1 High Availability Administration Guide.