One of the motivations for using an application server is to improve performance by off-loading tasks from the Web server. Common sense says that with heavy traffic — more users, more transactions, more data, more security checks — the more likely the Web server becomes a bottleneck. In some respects its simply a matter of processing power — Web browsers from hundreds (if not thousands) of users can place huge demands on a server, sometimes bringing it to a standstill. Of course, it is possible to offload some of this traffic to other Web servers. At some point, however, depending on the load, the type of applications, and the amount of control required it becomes not only more efficient but more manageable to move some of the workload to an application server.
What are the performance criteria for moving to an application server? The most obvious is an overloaded Web server — measured by whatever evaluation fits the particular situation. More to the point are the causes of the overload. Although not necessarily easy to pinpoint, if the causes seem to be one or more of the following an application server may be the ticket: Long response times retrieving or formatting data; transaction processing bottlenecks; complicated security and user validation; and special processing required for an application.