| The development and integration of computer technology and wireless communication technology have realized a brand new computing environment–mobile computing. The mobile computing accelerates the amalgamation of the wireless technology and distributed database technology, and that is mobile database. Within mobile database system, people can get needed data at any time from any location. But it brings new challenges for the data transmission, organizing, accessing and management, because of the immanent properties of the mobile environment such as mobility, frequent disconnection, low bandwidth of the wireless network, network heterogeneity, unbalanced network communication, user scalability, limited power etc. And so far, the study of mobile database has become a hot spot.In the mobile database system, mobile hosts will inevitably lead to system instability in the high failure rate, and therefore the study of mobile hosts'recovery technology has both theoretical and practical value. In the context of computing, check pointing and recovery scheme is a popular technique to recovery. This paper presents checkpoint protocol which can recovery asynchronously and take a checkpoint independently. The protocol simultaneously takes full account of disconnected treatment, cache operations, and handoff treatment of the mobile hosts. It bases on the conventional communicated model, adopts the way in the same cell, and it does not have message exchange between the mobile hosts. Finally the paper proves the correctness of the recovery protocol, and the recovery protocol is higher than that of traditional approaches in terms of recovery overhead.Because of the characteristics of mobile environment, the mobile host's logs dispersed at different cells. How to effectively manage the log affects the recovery efficiency of the mobile host. In this paper, it comes up with an effective log management strategy for mobile database based on proposed database system model. Based on the characteristics of the mobile database, the strategy manages the log according the region. In the region, the paper proposes a closing principle to store log, so all the log information can be collected from the mobile host at the nearby mobile support station. When mobile host recoveries from failure, it avoids the overhead of the log information generated by the distribution too wide, and improves the mobile host's ability to quickly restore from failure. |
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