The generalized tree quorum protocol

Abstract

In this paper, we present a low-cost fault-tolerant protocol for managing replicated data. We impose a logical tree structure on the set of copies of an object and develop a protocol that uses the information available in the logical structure to reduce the communication requirements for read and write operations. The tree quorum protocol is a generalization of the static voting protocol with two degrees of freedom for choosing quorums. In general, this results in significantly lower communication costs for comparable data availability. The protocol exhibits the property of graceful degradation, i.e., communication costs for executing operations are minimal in a failure-free environment but may increase as failures occur. This approach in designing distributed systems is desirable since it provides fault-tolerance without imposing unnecessary costs on the failure-free mode of operations.