WAS v8.5 > WebSphere applications > Data access resources > Data concepts > Relational resource adapters and JCAUse a single instance of a resource adapter
We can optimize server startup time by restricting certain resource adapters to a single runtime instance inside the Java Virtual Machine.
Also useful for testing and troubleshooting. We can isolate issue by enabling restrictions on one or more resource adapters involved in a problem.
Use with caution. Using this design does not allow two resource adapter JavaBeans instances that would return true from the equals method to coexist in the same JVM, if any one of them is configured as single-instance. For example, if two applications that have embedded the same resource adapter, or one application that embeds a resource adapter, and the same resource adapter is installed in the server as a stand-alone resource adapter, are configured on the same server such that even though some of their config attributes are different, the ones the equals() method evaluates are equal, this will no longer be allowed, and will return a ResourceException.
Some vendor resource adapters cannot tolerate multiple instances, and do not have a JCA-defined method of communicating this. The deployer must pro-actively configure resource adapter(s) for single-instance behavior.