The Availability and Performance of Epidemic Quorum Algorithms

Epidemic quorum systems enable highly available agreement even when a quorum is not simultaneously connected, making them suitable for weakly connected environments. Although recent work has proposed epidemic quorum algorithms, their availability and performance tradeoffs are not well studied. This paper formally defines generic epidemic quorum systems. The formalism unifies proposed epidemic quorum systems and is a framework for devising and studying epidemic coteries. We prove the safety of the resulting systems and analytically characterize their availability and performance. In particular, we identify previously undocumented trade-offs between both aspects that do not exist in the classical counterpart. Furthermore, we present analytical results comparing the availability and performance of relevant epidemic quorum systems, relating them to classical quorum systems.