Oracle Application Server provides several main high availability solutions for the middle-tier. For example:
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Single instance features: Each Oracle Application Server instance has built-in features, such as process failure detection and restart, configuration cloning, and intelligent routing, to improve availability.
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Clustering: A cluster is a set of application server instances that are configured to act in concert, providing increased availability and scalability. A cluster can span multiple hosts, leveraging the power of multiple CPUs while continuing to function despite the loss of any single instance or host.
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Load balancing: You can use Web Cache or an external load balancer in front of a set of instances to route requests to the most available instances.
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Session Replication: This solution is implemented using OC4J islands, which replicate session state among one another, providing backup in the event of a failure.
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Session Persistence: When using EJBs, you can use Entity Beans to represent business objects in a persistent storage mechanism.
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Distributed Cache: This solution is implemented using Oracle Application Server Java Object Cache, an "in-process" cache of Java objects that can be used on any Java platform by any Java application.
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