COM & .NET Component Services

Chapter 3.  COM+ Instance Management

A few years ago, the dominant programming model and design pattern was the client/server model. COM and DCOM were predominant component technologies, and all was well. Then came the Internet revolution. Almost overnight, a new paradigm emerged—the multitier architecture . Scalability is perhaps the single most important driving force behind the move from classic two-tier client/server to multitier applications. Today, being able to handle a very large number of clients is necessary for survival. The classic two-tier model simply does not scale well from a few dozen clients to tens of thousands of clients hammering on your system at peak load. The two-tier model of dedicating one server object per client quickly causes critical resources to dwindle under such loads. Allocating resources such as a database connection, a system handle, or a worker thread to each client is unrealistic. The middle tier was introduced precisely because you could no longer map client objects directly to your data processing objects. The middle tier allows pooling of resources, such as database connections, hardware objects, or communication ports. The middle tier also allows you to activate your objects just when they are required and release them as soon as possible.

COM+ provides you with two elegant and user-friendly instance management services that you can use to build scalability into your system design from day one: object pooling and Just-in-Time Activation ...