By default, a WebSphere application server uses session affinity. Session affinity allows WebSphere to assoicate requests from a certain browser to a certain JVM. For example, let's say you have two JVMs in a cluster. When a browser requests an application from the cluster, either JVM1 or JVM2 will send the browser the application. If JVM1 is the application server to send the browser the application, subsequent requests from the browser will route to JVM1, and will not invole JVM2. Likewise, if JVM2 were to send the application to the browser, then JVM2 would continue to answer the browsers requests, until the session is destroyed.
Session affinity improves performance, by allowing sessions to be accessed from cache in the application server, instead of having requests bounce between different application servers in a cluster.
Session affinity can be verified by checking the application server SystemOut.log file. When session affinity has been estabished with JVM1, only JVM1 SystemOut.log file should contain events from the browser. The same is true for JVM2.
~]# $was_home/profiles/<profile name>/servers/JVM1/logs/SystemOut.log ~]# $was_home/profiles/<profile name>/servers/JVM2/logs/SystemOut.log