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 may be used as a building block for performing updates and global queries on a distributed, shared information base. An e-intersecting quorum system is a distribution on sets such that every two sets from the distribution intersect with probability 1-epsilon. This relaxation of consistency results in a dramatic improvement of the load balancing and resilience of quorum systems, making the approach especially attractive for scalable and dynamic settings. In this paper we assume a dynamic model where nodes constantly join and leave the system. A quorum chosen at time s must evolve and transform as the system grows/shrinks in order to remain viable. For such a dynamic model, we introduce dynamic epsilon-intersecting quorum systems. A dynamic e-intersecting quorum system ensures that in spite of arbitrary changes in the system population, any two evolved quorums intersect with probability 1-epsilon.