Clustering in the EJB Tier

Single VM Versus Multiple VM Architectures

We should make one final note about load balancing in EJB servers. Some EJB vendors provide load balancing with a multiple-VM architecture, rather than just clustering EJB objects. For example, the application server from Gemstone, Gemstone/J, provides what it calls Extreme Clustering. It uses a JVM pool where multiple Java Virtual Machines are created and maintained in a pool that can grow and shrink dynamically.

The JVMs can be pooled and tuned for specific responsibilities within the enterprise application. Their approach to load balancing is unique and has some nice features that others don't support. Whether this architecture is the correct one for your system is best determined by comparing the features against other vendors. You can get more information on the Gemstone product and its Extreme Clustering technique by going to the Gemstone Web site at http://www.gemstone.com.