A Distributed Quorum System for Ensuring Bounded Staleness of Key-Value Stores

Modern storage systems employing quorum replication are often configured to use partial, non-strict quorums to prioritize performance over consistency. These systems return the most recently changed data item only from a set of replicas to respond more quickly to a read request without guaranteeing that the data item is the most recently changed for all of the data. Because these partial quorum mechanisms provide only basic eventual consistency guarantees, with no limit on the freshness of the data returned, sometimes these configurations are not acceptable for certain applications. In this work, we have devised a new key-value store with partial quorums while ensuring bounded staleness. Our store reports the expected bounds on staleness with respect to wall clock. We evaluated our new key-value store with Yahoo! Cloud Service Benchmarks and show its performance.