Optimizing Vote and Quorum Assignments for Reading and Writing Replicated Data

In the weighted voting protocol which is used to maintain the consistency of replicated data, the availability of the data to read and write operations not only depends on the availability of the nodes storing the data but also on the vote and quorum assignments used. We consider the problem of determining the vote and quorum assignments that yield the best permormance in a distributed system where node availabilities can be diierent and the mix of the read and write operations is arbitrary. The optimal vote and quorum assignments depend not only on the system parameters such as node availability and operation mix, but also on the performance measure. We present an enumeration algorithm that can be used to nd the vote and quorum assignments that need to be considered for achieving optimal performance. When the performance measure is data availability, an analytical method is derived to evaluate it for any vote and quorum assignment. This method and the enumeration algorithm is used to nd the optimal vote and quorum assignment for several systems. The enumeration algorithm can also be used to obtain the optimal performance when other measures are considered.