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Federating Consistency for Partition-Prone Networks
Benjamin Bengfort and Pete Keleher
University of Maryland, University of Maryland

Groups of strongly consistent devices can efficiently order events under ideal (data center) conditions, but become less effective in dynamic and heterogeneous environments. Weakly consistent devices efficiently tolerate both faults and dynamic conditions but are slow to converge on a single ordering of system events. We propose “federated consistency”, which combines the strengths of both approaches into a single protocol. Federated groups use a strongly consistent inner core of devices to maintain a totally ordered, fault-tolerant sequence of events. A cloud of weakly-consistent devices disseminates orderings and enables progress despite varying connectivity and partitions. Though the constituent sub-protocols take different (nearly opposite) approaches to resolving conflicts; we show that expanding distributed version vectors with a forte component allows them to inter-operate effectively. We use a discrete event simulation to show that a group of federated devices can obtain the key advantages of both approaches. Such systems have been investigated before [1], [2], but our approach targets more active “weak nodes” in a wide-area setting.