Crumbling walls: a class of practical and efficient quorum systems
Proceedings of the fourteenth annual ACM symposium on Principles of distributed computing
Access control and signatures via quorum secret sharing
CCS '96 Proceedings of the 3rd ACM conference on Computer and communications security
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A quorum system is a collection of sets (quorums) every two of which intersect. Quorum systems have been used for many applications in the area of distributed systems, including mutual exclusion, data replication and dissemination of information. Given a strategy to pick quorums, the load L(S) is the minimal access probability of the busiest element, minimizing over the strategies. The capacity Cap(S) is the highest quorum access rate that S can handle. We show that for any quorum system, Cap(S) = 1/L(S). The availability of a quorum system S is the probability that at least one quorum survives, assuming that each element fails independently with probability p. A tradeoff between L(S) and the availability of S is shown. None of the existing constructions of quorum systems achieves simultaneously good availability and low load. We present four novel constructions of quorum systems, all featuring optimal or near optimal load, and high availability. The best construction, based on paths in a grid, has a load of O(1/On), and a failure probability of exp(-L(On)) when the elements fail with probability p 1/sub/sub