Concurrent Database Updates during Disconnection in Mobile Computing Environments (Special Issue on ITS and Mobile Computing)

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In mobile computing environments, the limitations of mobile computers and wireless networks cause frequent disconnections among the hosts. Consequently, transactions on databases at disconnected sites cannot be executed smoothly without creating problems of inconsistency among copies of data. In this paper, we discuss how to minimize this problem. We assume that a database can be divided into clusters according to the data access pattern and that, for each cluster, the probability of transactions occurring is constant and known. We also assume that most of the disconnections are intentional and that no two disconnections can coexist. On the basis of the probability that transactions occur and the duration of the disconnection between the sites, our approach chooses whichever is more appropriate, the token method or the optimistic method, to control database updates. The token method enables a single site to execute transactions during disconnection, and thus ensures that no conflicts occur between the transactions. The optimistic method lets multiple disconnected sites execute transactions simultaneously. Conflicts are checked upon reconnection, and roll-back of transactions is performed if necessary. The evaluation functions of both methods are derived on the basis of the number of transactions expected to succeed during the disconnection period and the waiting time of these transactions before they can be committed. Whichever method gives a higher evaluation function value is chosen.
一般社団法人情報処理学会の論文
2001-07-15

Concurrent Database Updates during Disconnection in Mobile Computing Environments (Special Issue on ITS and Mobile Computing)

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