Consistency management in Deno

Abstract

We describe a new replicateddobject protocol designed for use in mobile and weaklydconnected environments. The protocol differs from previous protocols in combining epidemic information propagation with voting, and in using fixed perdobject currencies for voting. The advantage of epidemic protocols is that data movement only requires pairdwise communication. Hence, there is no need for a majority quorum to be available and simultaneously connected at any single time. The protocols increase availability by using voting, rather than primarydcopy or primarydcommit schemes. Finally, the use of perdobject currencies allows voting to take place in an entirely decentralized fashion, without any server having complete knowledge of group membership. We show that currency allocation can be used to implement diverse policies. For example, uniform currency distributions emulate traditional voting schemes, while allocating all currency to a single server emulates a primarydcopy scheme. We present simulation results showing both schemes, as well as the performance advantages of using currency proxies to temporarily reallocate currency during planned disconnections. Furthermore, we discuss an initial design of the underlying replicateddobject system and present a basic API.