Using control theory to achieve service level objectives in performance management (Q698468)

A widely used approach to achieving service level objectives for a software system is to add a controller that manipulates the target system's tuning parameters. A methodology for designing such controllers for software systems that builds on classical control theory is described. The classical approach proceeds in two steps: system identification and controller design. In system identification, the mathematical models of the target system are constructed. In controller design, an analysis of the models leads to a controller that will achieve the service level objectives. An analysis of a closed-loop system using an integral control law with Lotus Notes as the target is reported. The objective is to maintain a reference queue length. Using root-locus analysis from control theory it is possible to predict the occurrence of controller-unclouded oscillations in the system's response. Such oscillations are undesirable since they increase variability, thereby resulting in a failure to meet the service level objective. This controller is implemented for a real Lotus Notes system, and a remarkable correspondence between the behaviour of the real system and the predictions of the analysis is observed.