Strengthening consistency in the Cassandra distributed key-value store

Abstract

Distributed highly-available key-value stores have emerged as important building blocks for applications handling large amounts of data. The Apache Cassandra system is one such popular store combining a key distribution mechanism based on consistent hashing with eventually-consistent data replication and membership mechanisms. Cassandra fits well applications that share its semantics but is a poor choice for traditional applications that require strong data consistency. In this work we strengthen the consistency of Cassandra through the use of appropriate components: the Oracle Berkeley DB Java Edition High Availability storage engine for data replication and a replicated directory for maintaining membership information. The first component ensures that data replicas remain consistent despite failures. The second component simplifies Cassandra's membership, improving its consistency and availability. In this short note we argue that the resulting system fits a wider range of applications, and is more robust and easier to reason about. © 2013 IFIP International Federation for Information Processing.