Any time that an application can obtain the data it needs from the application tier, it is eliminating the data source as the Single Point Of Bottleneck (SPOB).

To address the potential scalability limits of the replicated cache service, both in terms of memory and communication bottlenecks, Oracle Coherence provides a distributed cache service. Many products have used the term distributed cache to describe their functionality, so it is worth clarifying exactly what is meant by that term in Oracle Coherence. Oracle Coherence defines a distributed cache as a collection of data that is distributed (or, partitioned) across any number of cluster nodes such that exactly one node in the cluster is responsible for each piece of data in the cache, and the responsibility is distributed (or, load-balanced) among the cluster nodes.

There are several key points to consider about a distributed cache:

• Partitioned: The data in a distributed cache is spread out over all the servers in such a way that no two servers are responsible for the same piece of cached data. This means that the size of the cache and the processing power associated with the management of the cache can grow linearly with the size of the cluster. Also, it means that operations against data in the cache can be accomplished with a "single hop," in other words, involving at most one other server.
• Load-Balanced: Since the data is spread out evenly over the servers, the responsibility for managing the data is automatically load-balanced across the cluster.
• Location Transparency: Although the data is spread out across cluster nodes, the exact same API is used to access the data, and the same behavior is provided by each of the API methods. This is called location transparency, which means that the developer does not have to code based on the topology of the cache, since the API and its behavior will be the same with a local JCache, a replicated cache, or a distributed cache.
• Failover: All Oracle Coherence services provide failover and failback without any data loss, and that includes the distributed cache service. The distributed cache service allows the number of backups to be configured; as long as the number of backups is one or higher, any cluster node can fail without the loss of data.