An Adaptive Cache Management Scheme For Mobile Database

With the development of the wireless communication technology and mobile devices, the mobile environment increasingly mature, and mobile computing has become a hot research topic today. The research on mobile database technology that also called distributed databases technology which supports the mobile computing environment has become a new direction of the distributed database. Cache technology is one key technology of mobile database. One main object of mobile database is to ensure the validity of accessed data under disconnection. So caching of frequently accessed data at the mobile clients is an effective technology to improve mobile environmental performance.A new model is presented on the basis of cache and data broadcast, which includes two parts: the fixed network and the wireless network. The fixed network, connecting the fixed devices, includes several broadcast server and Home Mobile Support Station. The MSS is responsible for connecting the broadcast server and mobile clients. The wireless network, composed of mobile devices, enables mobile clients communicating with the broadcast server by MSS to maintain data consistency between cache and the server.A new adaptive cache management scheme (ACMS) for mobile database is proposed by analysis of the traditional cache invalidation mechanisms based on invalidation reports. In this mechanism, by utilizing a counter on the basis of the timestamps to record the number of mobile clients requesting to the server; at the server side, dynamically adjust the contents of invalidation reports and broadcast interval in accordance with the number of mobile clients accessing the data, and send to mobile clients; at the client side, the mobile clients judge the validity of the contents in cache by the timestamps and broadcast interval, and amend the state of cache so as to implement the dynamic management of the cache.The proposed algorithm is evaluated by experimental simulation, results show that this method can adapt to the characteristics of the mobile environment much more effectively, such as the deficiency bandwidth, the asymmetry of up-down-stream link, and the frequent disconnect of the network, and effective improve the bandwidth utilization, thereby enhancing the efficiency of the cache technology, data availability and consistency of mobile database.