On improving performance and conserving power in cluster-based web servers

Efficiency and power conservation are critical issues in the design of cluster systems because these two parameters have direct implications on the user experience and the global need to conserve power. Widely adopted, distributor-based systems forward client requests to a balanced set of waiting servers in complete transparency to the clients. The policy employed in forwarding requests from the front-end distributor to the backend servers plays an important role in the overall system performance. Existing research separately addresses server performance and power conservation. The locality-aware request distribution (LARD) scheme improves the system response time by having the requests served by web servers which have the data in their cache. The power-aware request distribution aims at reducing the power consumption by turning the web servers OFF and ON according to the load. This research tries to achieve power conservation while preserving the performance of the system. First, we prove that using both power-aware and locality-aware request distribution together provides optimum power conservation, while still maintaining the required QoS of the system. We apply the usage of pinned memory in the backend servers to boost performance along with a request distributor design based on power and locality considerations. Secondly, we employ an intelligent-proactive-distribution policy at the front-end to improve the distribution scheme and complementary pre-fetching at the backend server nodes. The proactive distribution depends on both online and offline analysis of the website log files, which capture user navigation patterns on the website. The prefetching scheme pre-fetches the web pages into the memory based on a confidence value of the web page predicted by backend using the log file analysis. Designed to work with the prevailing web technologies, such as HTTP 1.1, our scheme provides reduced response time to the clients and improved power conservation at the backend server cluster. Simulations carried out with traces derived from the log files of real web servers witness performance boost of 15-45% and 10-40% power conservation in comparison to the existing distribution policies.