Eager Replication for Stateful J2EE Servers
Replication has been widely used in J2EE servers for reliability and scalability. There are two properties which are important for a stateful J2EE application server. Firstly, the state of the server and the state of the backend databases should always be consistent. Secondly, each request from a client should be executed exactly once. In this paper, we propose a replication algorithm that provides both properties. We use passive replication where a primary server executes a request, and all state changed within the application server by this request is sent to the backup replicas at the end of the execution. An agreement protocol guarantees the consistency between the state of all replicas and the database. A client side communication stub automatically resubmits requests in case of failures, and unnecessary resubmissions are detected by the server replicas. We have implemented the algorithm and integrated it into the JBoss application server. A performance study using the ECPerf benchmark shows the feasibility of our approach.
Proc. of the Int. Symposium on Distributed Objects and Applications, Agia Napa, Cyprus, October 2004.
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