Venkat Tadakamalla and Daniel A. Menasce ́
Many computer systems, such as Internet datacenters and cloud computing environments, consist of a multitude of servers that process user requests. Incoming requests that find all servers busy have to wait until a server becomes idle. This type of queuing system is known as a G/G/c system and has been extensively studied in the queuing literature under steady state con- ditions. This paper studies multi-server systems subject to workload surges of generic trapezoidal shapes during which the average arrival rate of requests exceeds the system’s capacity. This paper’s main contributions are: (1) Generic equations for surges of any shape. (2) A set of equations to estimate the impact of trapezoidal and triangular shaped surges on response time. (3) The design, implementation, and extensive evaluation of an autonomic controller for cloud server elasticity using a G/G/c simulator previously developed by the authors. The results show that our equations estimate with great accuracy the impact of surges on response time and that our autonomic controllers are able to successfully vary the number of servers to mitigate the impact of workload surges.