Probabilistic quorums for dynamic systems

A quorum system is a set of sets such that every two sets in the quorum system intersect. Quorum systems are well known building blocks for maintaining information in a distributed system while providing high availability and good load balance. Probabilistic Quorum Systems (PQS) are variants of quorum systems that relax the strict intersection requirement. They are particularly attractive for large scale systems due to their simplicity and highly efficient availability—load balance tradeoff. We introduce scalable techniques that maintain a PQS in a highly decentralized and highly dynamic setting. We address two challenges. First we show how PQS can be realized efficiently even when each process maintains knowledge of only a constant number of other members. Second, we provide algorithms that adaptively evolve the quorums to adjust to the changes in the system caused by processes leaving and joining the system over time.