A Versatile Family of Consensus Protocols Based on Chandra-Toueg's Unreliable Failure Detectors

This paper is on consensus protocols for asynchronous distributed systems prone to process crashes, but equipped with Chandra-Toueg's (1996) unreliable failure detectors. It presents a unifying approach based on two orthogonal versatility dimensions. The first concerns the class of the underlying failure detector. An instantiation can consider any failure detector of the class S (provided that at least one process does not crash), or oS (provided that a majority of processes do not crash). The second versatility dimension concerns the message exchange pattern used during each round of the protocol. This pattern (and, consequently, the round message cost) can be defined for each round separately, varying from O(n) (centralized pattern) to O(n/sup 2/) (fully distributed pattern), n being the number of processes. The resulting versatile protocol has nice features and actually gives rise to a large and well-identified family of failure detector-based consensus protocols. Interestingly, this family includes at once new protocols and some well-known protocols (e.g., Chandra-Toueg's oS-based protocol). The approach is also interesting from a methodological point of view. It provides a precise characterization of the two sets of processes that, during a round, have to receive messages for a decision to be taken (liveness) and for a single value to be decided (safety), respectively. Interestingly, the versatility of the protocol is not restricted to failure detectors: a simple timer-based instance provides a consensus protocol suited to partially synchronous systems.