Shortest remaining response time scheduling for improved web server performance

Abstract

The Shortest-Remaining-Response-Time (SRRT) policy has been proposed for scheduling static HTTP requests in web servers to reduce the mean response time. The SRRT prioritizes requests based on a combination of the current round-trip-time (RTT), TCP congestion window size (cwnd) and the size of what remains of the requested file. We compare SRRT to Shortest- Remaining-Processing-Time (SRPT) and Processor-Sharing (PS) policies. The SRRT shows the best improvement in the mean response time. SRRT gives an average improvement of about 7.5% over SRPT. This improvement comes at a negligible expense in response time for long requests. We found that under 100Mbps link, only 1.5% of long requests have longer response times than under PS. The longest request under SRRT has an increase in response time by a factor 1.7 over PS. For 10Mbps link, only 2.4% of requests are penalized, and SRRT increases the longest request time by a factor 2.2 over PS.