SOFTWARE BOTTLENECKING IN CLIENT-SERVER SYSTEMS AND RENDEZVOUS NETWORKS

Software bottlenecks are performance constraints caused by slow execut ion 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 re quests, so a saturated server will slow down all its clients. A Rendez vous Network generalizes this relationship to multiple layers of serve rs with send-and-wait interactions (rendezvous), a two-phase model of task behavior, and to a unified model for hardware and software conven tion. software bottlenecks have different symptoms, different behavior when the system is altered, and a different cure from the conventiona l bottlenecks seen in queueing network models of computer systems, cau sed by hardware limits. The differences are due to the ''push-back'' e ffect of the rendezvous, which spreads the saturation of a server to i ts clients. The paper describes software bottlenecks by examples, give s a definition, shows bow they can be located and alleviated, and give s a method for estimating the performance benefit to be obtained. Ulti mately, if all the software bottlenecks can be removed, the performanc e limit will be due to a conventional hardware bottleneck.