Figure 4
Two serially connected M/M/m queues. Queueing system composed by two M/M/m queues connected serially. The first one models the access to the primary servers, and the second one models the access to the database. λ is the request arrival rate. There is a probability d of accessing the second queue, and a probability (1−d) of exiting the queueing system without going through the second queue.