On Exploiting Locality for Generalized Consensus

Single leader-based Consensus protocols are known to stop scaling once the leader reaches its saturation point. On the other hand, establishing Consensus of commands by taking into account only their dependencies (as specified by Generalized Consensus) is appealing because of the potentially higher parallelism and lower latency. However, current solutions have well-known pitfalls due to the higher quorum size, which is required to exploit low-latency fast decisions, and the need for tracking dependency relations. In this paper we briefly introduce M2PAXOS, a new implementation of Generalized Consensus that provides a fast decision of commands by leveraging a classic quorum size, which matches just the majority of nodes deployed. M²PAXOS does not establish command dependencies based on conflicts, rather it associates accessed objects with nodes, so that the delivery decision of commands operating on the same objects is made by a common node. The evaluation study of M2PAXOS confirms its effectiveness by showing an improvement up to 7× over state-of-the-art (Generalized) Consensus protocols.