Clock-RSM: Low-Latency Inter-datacenter State Machine Replication Using Loosely Synchronized Physical Clocks

This paper proposes Clock-RSM, a new state machine replication protocol that uses loosely synchronized physical clocks to totally order commands for geo-replicated services. Clock-RSM assumes realistic non-uniform latencies among replicas located at different data centers. It provides low-latency linearizable replication by overlapping 1) logging a command at a majority of replicas, 2) determining the stable order of the command from the farthest replica, and 3) notifying the commit of the command to all replicas. We evaluate Clock-RSM analytically and derive the expected command replication latency. We also evaluate the protocol experimentally using a geo-replicated key-value store deployed across multiple Amazon EC2 data centers.