Software Bottlenecking in Client-Server Systems and Rendezvous Networks

Software Bottlenecks are performance constraints caused by slow execution of a software task. In typical client-server systems a client task must wait in a blocked state for the server task to respond to its requests, so a saturated server will slow down all its clients. A Rendezvous Network generalizes this relationship to multiple layers of servers with send-and-wait interactions (rendezvous), a two-phase model of task behaviour, and to a unified model for hardware and software contention. Software bottlenecks have different symptoms, different behaviour when the system is altered, and a different cure from the conventional bottlenecks seen in queueing network models of computer systems, caused by hardware limits. The differences are due to the "push-back" effect of the rendezvous, which spreads the saturation of a server to its clients. The paper describes software bottlenecks by examples, gives a definition, shows how they can be located and alleviated, and gives a method for estim..