Modeling and Control of Google bittide Synchronization

Distributed system applications rely on a fine-grain common sense of time. Existing systems maintain the common sense of time by keeping each independent machine as close as possible to wall-clock time through a combination of software protocols like NTP and GPS signals and/or precision references like atomic clocks. This approach is expensive and has tolerance limitations that require protocols to deal with asynchrony and its performance consequences. Moreover, at data-center scale it is impractical to distribute a physical clock as is done on a chip or printed circuit board. In this paper we introduce a distributed system design that removes the need for physical clock distribution or mechanisms for maintaining close alignment to wall-clock time, and instead provides applications with a perfectly synchronized logical clock. We discuss the abstract frame model (AFM), a mathematical model that underpins the system synchronization. The model is based on the rate of communication between nodes in a topology without requiring a global clock. We show that there are families of controllers that satisfy the properties required for existence and uniqueness of solutions to the AFM, and give examples.