Eager Replication for Stateful J2EE Servers
H. Wu, B. Kemme, V. Maverick
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
Proc. of the Int. Symposium on Distributed Objects and
Applications, Agia Napa, Cyprus, October 2004.
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