When available Coherence will utilize either sun.misc.AtomicLong or java.util.concurrent.atomic.AtomicLong (1.5 only) to implement concurrent counters. If neither of these is available Coherence will use a somewhat less performant synchronized counter, and output the following warning.
sun.misc.AtomicLong is not supported on this JVM; using a synchronized counter.
Though it is safe to ignore this message, if possible it may be best to address it.
If you are using a Sun 1.4 or higher JVM, simply running the JVM in server mode allows the use of the concurrent counter, as well as providing a number of other JVM performance improvements associated with the server JVM setting. Server mode can be specified by including "-server" on the JVM command line.
If using a non-Sun JVM, upgrading to the vendor's 1.5 or higher JVM will allow support for concurrent counters.