Scaling for E-Business

8.5. Queues, Waiting Time, and Response Time

During its execution, a transaction in e-commerce systems is serviced by many different resources, such as Web servers, database servers, and payment servers. Each time a transaction or request visits a resource, it may need to queue for the use of the resource. Figure 8.10(a) shows the graphical notation used to represent a resource (a circle) and its queue (striped rectangle). The resource in the case of Fig. 8.10(a) could be an authentication server, and the striped rectangle would represent the queue of transactions waiting to be authenticated by the server. From Fig. 8.10-a, we notice that

Figure 8.10. Graphical Representations of a Resource and Its Queue.

Equation 8.5.15

where response time ...