A Proxy-Based Self-tuned Overload Control for Multi-tiered Server Systems

Abstract

Web-sites, especially E-commerce ones, are often faced with incoming load of requests that exceeds their capacity, i.e, they are subjected to overload. Most existing servers show severe throughput degradation at high overload. Overload control mechanisms are required to prevent such occurrences. In this paper, we present a proxy-based overload control mechanism, which uses the drop in throughput relative to arrival rate as an indicator of overload. On overload detection, a self-clocked admission control is activated, which admits a new request only when a successful reply is observed to be leaving the server system. Thus, the mechanism is self-tuned, and requires no knowledge of the system. We validate our approach on an experimental testbed consisting of a two-tier Web application, and find that even at very high overload, the server operates at its maximum capacity while keeping response times within acceptable bounds.