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In distributed databases, oriented toward general business software such as groupware, the asynchronous update method is widely used in order to align the databases. In this method, each database has replicas of the other databases, and the replicas are updated at the same time according to a predetermined replica routing schedule. This paper discusses an approximate method for minimizing the communication cost and time needed for updating the replicas in such a distributed database. More precisely, the case in which the communication cost is proportional to the amount of transferred data is considered, and an optimization problem is formulated in which the replication routing schedule minimizing the time for the replica update is to be determined from those minimizing the communication cost for the replica update. An approximate solution for the formulated problem is presented. Then the result of evaluation of the approximate replication routing schedule obtained as the approximate solution is discussed, and it is shown that the communication cost for replica update is minimized and that the time for the replica update is at most 1.2 times the minimum value if the number of distributed databases is at most 7. © 2001 Scripta Technica, Electron Comm Jpn Pt 1, 85(4): 61–70, 2002 [ABSTRACT FROM AUTHOR]

In distributed databases for general-purpose business software, such as groupware, the asynchronous replication update method is widely employed to assure coincidence in the contents of the database; the replications of other databases retained in each database are updated simultaneously according to a predetermined schedule. This article discusses the approximate scheduling in such a distributed database that minimizes the communications cost of updating the replications. More precisely, as the first step, we consider the case in which two-way concurrent transmission is allowed in each link, and the communications cost is proportional to the communication time required for the transfer. The problem of deriving the schedule to minimize the communications cost is formulated. As a practical method of solving that problem, a heuristic method that effectively derives the approximate schedule with a communications cost close to the minimum is proposed. A quantitative evaluation of the proposed method is presented, and it is shown that a schedule very close to the optimal solution is obtained if the communications cost coefficient of the links is almost the same. © 1999 Scripta Technica, Electron Comm Jpn Pt 1, 83(1): 73–86, 2000 [ABSTRACT FROM AUTHOR]