为了对抗软件老化，提出一种细粒度的、事前的、主动的多级软件抗衰技术。通过分析系统资源的 占用和损耗情况，判定系统性能的衰退规律，并据此制定了基于时间的多级软件抗衰策略和基于检测的多级软 件抗衰策略，采用有限状态自动机对两种策略进行形式化描述，最后通过Web服务案例说明策略的制定过程， 给出仿真结果。实验表明，较之单一系统级软件抗衰，多级抗衰策略可以进一步缩短MTTR，提供更高的系统可 用性，同时将抗衰成本降到更低。

Recently,the phenomenon of software aging,one in which error conditions actually accrue with time and/or load,has been observed. To counteract software aging, which can cause outages resulting in high costs,a proactive restart technique called software rejuvenation is proposed and the rejuvenation cost is analyzed.In order to reduce the rejuvenation cost and improve software availability and reliability further, rejuvenation granularity should be finer than before. Therefore a fine-grained proactive technique——multilevel software rejuvenation is put forward. Firstly, the degradation law of system performance can be determined by analyzing the occupation and wastage of system resources. Based on the law and the software architecture,the two software rejuvenation policies, i.e. time-based multilevel software rejuvenation policy and detection-based multilevel software rejuvenation policy, can be drafted, and the rejuvenation granularity can be determined. Their formal description of policies is given by finite-state automaton. Finally, the entire process is illustrated with a web service case. This paper provides a case to illustrate the process, and the simulation results of the case show that the multilevel software rejuvenation policy can reduce the MTTR and rejuvenation cost further, comparing with the only system-level software rejuvenation. As a consequence,the system availability and reliability are enhanced.

游静（1975－），女，河北石家庄市人，博士，江苏工业学院讲师