Abstract: Control theory is being used for QoS in Web server, but when workload varies significantly, the real-time performance of the feedback control needs to be improved. After analysing the heavy-tailed property of the number and size of embedded URL in the required pages,based on the ctueuing feature of the Web server and the HTTP 1. 1 persistent connection,a predictive approach was desired to achieve the relative delay guarantee by calculating the future delay of the different priorities and adjusting their ctuota of service threads. The experimental results demonstrate that the pro- posed approach achieves a better dynamic performance.

Key words: Web QoS, Predictive control, Proportional delay guarantee, Heavy-tailed distribution