A feedback control approach for software rejuvenation in a web server

Software aging refers to the phenomenon that applications will show growing failure rate or performance degradation after longtime execution. This phenomenon usually results from the accumulation of error conditions, such as memory leaks, round-off errors, file tables not released, etc. Unexpected downtime cost due to software aging is huge, particularly for e-commerce Websites and safety/business-critical applications. Software rejuvenation is an effective but expensive fault tolerance technique to deal with software aging phenomenon. This technique usually involves the termination of services due to the restart of computer systems. In this paper, a ¿lightweight¿ complementary technique of software rejuvenation is proposed to reduce the severity of software aging in terms of its impact on system resource usage by online tuning the settings of related parameters. Unlike traditional software restart involved in traditional rejuvenation, this technique is based on the idea of fine adjustment of software state. Experiments are conducted to reveal the relationship between certain parameters of Web server and resource usage. Accordingly, a PI (proportional-integral) controller is designed to online tune the parameters of web server with the purpose of counteracting the effect of software aging. Simulation results show that the technique is cost-effective.