Scalable but wasteful: Current state of replication in the cloud

Abstract

Consensus protocols are at the core of strongly consistent replication deployed in cloud-based storage systems. There have been many proposals to optimize these protocols, most of which work by identifying and shifting load from bottlenecked nodes to underutilized nodes. We show that while these optimizations increase throughput, they sacrifice resource efficiency, which is paramount in a cloud setting. We propose a new metric to measure the efficiency of these protocols and show that using this metric, for example, the optimized EPaxos protocol is less efficient than the unoptimized Multi-Paxos protocol. We then demonstrate that Multi-Paxos can achieve 2$\times$ higher throughput than EPaxos in a fixed-budget resource setting that is typical of the cloud. Our work underlines the need for considering resource efficiency when optimizing consensus protocols, given that they are increasingly deployed in the cloud.