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Optimal cost design of replicated data in distributed database systems

Replicated data are a common strategy for achieving ultra-availability in fault-tolerant distributed database systems. Replication, however, requires additional resources, for example additional costs in terms of maintenance effort, software complexity, hardware requirements and time needed for testing consistency. Various replication control protocols have been developed to ensure data consistency. In this paper, we develop analytical methods for the quorum-consensus replication protocol that minimizes the total system cost by determining the optimal read quorum, the optimal number of system sites, or the optimal site availability assuming that (1) the cost of an individual site is an increasing function of the availability of the site and (2) the two system unavailable modes (i.e. read and write) can have different penalty costs. Several numerical examples and applications are provided to illustrate the results.