WebSphere Application Server provides a service that transfers data or events among WebSphere Application Server servers. The service is called WebSphere Internal Replication, or replication for short.
The replication service transfers both J2EE application data and any internal data used to maintain the application data among WebSphere run-time processes in a cluster of application servers.
Currently, the Web container in WebSphere Application Server leverages replication.
The replication service can replicate HttpSession data among processes and retrieve the HttpSession if the process that currently maintains the HttpSession fails. Using replication for HttpSession failover provides a potentially lower cost and more easily administrable alternative to storing HttpSession in a relational database. Further, the service can distribute across a WebSphere cluster information on invalid data and actual cached data maintained by a Web container's dynamic caching.
URL link: http://publib7b.boulder.ibm.com/wasinfo1/en/info/ae/ae/crun_repl.html