Abstract
It is common that Internet service hosting centres use several logical pools to assign server resources to different applications, and that they try to achieve the highest total revenue by making efficient use of these resources. In this paper, multi-tiered enterprise systems are modelled as multi-class closed queueing networks, with each network station corresponding to each application tier. In such queueing networks, bottlenecks can limit overall system performance, and thus should be avoided. We propose a bottleneck-aware server switching policy, which responds to system bottlenecks and switches servers to alleviate these problems as necessary. The switching engine compares the benefits and penalties of a potential switch, and makes a decision as to whether it is likely to be worthwhile switching. We also propose a simple admission control scheme, in addition to the switching policy, to deal with system overloading and optimise the total revenue of multiple applications in the hosting centre. Performance evaluation has been done via simulation and results are compared with those from a proportional switching policy and also a system that implements no switching policy. The experimental results show that the combination of the bottleneck-aware switching policy and the admission control scheme consistently outperforms the other two policies in terms of revenue contribution.