Membership is established using multicast heartbeats. Hence, if you wish to subdivide your clusters, you can do this by changing the multicast IP address or port in the <Membership> element.
The heartbeat contains the IP address of the Tomcat node and the TCP port that Tomcat listens to for replication traffic. All data communication happens over TCP.
The ReplicationValve is used to find out when the request has been completed and initiate the replication, if any. Data is only replicated if the session has changed (by calling setAttribute or removeAttribute on the session).
One of the most important performance considerations is the synchronous versus asynchronous replication. In a synchronous replication mode the request doesn’t return until the replicated session has been sent over the wire and reinstantiated on all the other cluster nodes. Synchronous vs. asynchronous is configured using the channelSendOptions flag and is an integer value. The default value for the SimpleTcpCluster/DeltaManagercombo is 8, which is asynchronous. You can read more on the send flag(overview) or the send flag(javadoc). During async replication, the request is returned before the data has been replicated. async replication yields shorter request times, and synchronous replication guarantees the session to be replicated before the request returns.
