Consider a chain of processes P1, P2, ..., Pn implementing a multitiered client-server architecture. Process Pi is client of process Pi+1, and Pi will return a reply to Pi1 only after receiving a reply from Pi+1. What are the main problems with this organisation when taking a look at the request-reply performance at process P1?
Performance can be expected to be bad for large n. The problem is that each communication between two successive layers is, in principle, between two different machines. Consequently, the performance between P1 and P2 may also be determined by n - 2 request-reply interactions between the other layers. Another problem is that if one machine in the chain performs badly or is even temporarily unreachable, then this will immediately degrade the performance at the highest level.