Improving response time in cluster-based Web servers through coscheduling

In this paper, we investigate the feasibility of minimizing the response time of a Web server by exploiting the advantages of both user-level communication and coscheduling. We, thus, propose a coscheduled server model, based on the PRESS design where the remote cache accesses can be coscheduled on different nodes to reduce the response time. We experiment this concept using two known coscheduling techniques, called Dynamic Coscheduling (DCS) and DCS with immediate blocking. Extensive simulation of four server models (PRESS over TCP/IP, PRESS over VIA, coscheduled PRESS model with DCS, and with DCS and blocking) using 16-node and 32-node cluster configurations indicates that the average response time of a distributed server can be minimized significantly by coscheduling the communicating processes. The use of the DCS scheme reduced the average latency up to 80%, on an average 40%, compared to the PRESS over VIA model that uses only user-level communication, and by order of magnitude compared to the TCP/IP model. The throughput of the three user-level communication models is at least 25% better compared to the PRESS over TCP/IP model. Experiments with varying file size and cache size also confirmed the advantage of using a coscheduling mechanism for improving the response time behavior.