One of the most popular use cases for Oracle Service Bus (OSB) is the mediation of synchronous service interactions. In this scenario, a client invokes the service through a proxy instead of the actual service endpoint, guaranteeing that the consumer is decoupled from the producer. This type of architecture allows producers to be changed without impacting the consumers, allowing greater agility for projects with volatile requirements.
Synchronous services that return results that do not change often are good candidates to have their results cached by OSB, through a feature called Result Caching. This improves performance by reducing network overhead to access the back-end service. Result caching can help to improve scalability by reducing the load on the back-end servers that host the service. Figure 1 illustrates a client invoking a synchronous service with Result Caching enabled.
Although using the Result Caching feature may seem to always be a good idea, it is important to evaluate its side effects. When this feature is activated, all results are cached in the JVM heap. That means that heap can rapidly become full after a number of service invocations occur. This could lead to serious garbage collection (GC) issues once the JVM starts to reclaim the used space when it hits the high water-mark of 80% of the heap size. Eventually, full GC pauses will start to occur and jeopardize OSB performance.
To avoid using too much heap space with Result Caching, out-of-process Coherence servers can be set up to run in their own JVMs to hold the cached results. They are termed “out-of-process” because they execute in a JVM different from the OSB JVM. The technique here is to allocate data off the OSB JVM letting the Coherence servers use their own heap space without affecting the heap space OSB uses to process messages. This technique is also called off-heap caching. Figure 2 shows an OSB domain using out-of-process Coherence servers to hold the cached results. Read the complete article here.
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