Making sense of relativistic distributed systems

Abstract

Linearizability, a widely-accepted correctness property for shared objects, is grounded in classical physics. Its definition assumes a total temporal order over invocation and response events, which is tantamount to assuming the existence of a global clock that determines the time of each event. By contrast, according to Einstein’s theory of relativity, there can be no global clock: time itself is relative. For example, given two events A and B, one observer may perceive A occurring before B, another may perceive B occurring before A, and yet another may perceive A and B occurring simultaneously,with respect to local time. Here, we generalize linearizability for relativistic distributed systems using techniques that do not rely on a global clock. Our novel correctness property, called relativistic linearizability, is instead defined in terms of causality. However, in contrast to standard “causal consistency,” our interpretation defines relativistic linearizability in a manner that retains the important locality property of linearizability. That is, a collection of shared objects behaves in a relativistically linearizable way if and only if each object individually behaves in a relativistically linearizable way.