Shared State Consistency for Time-sensitive Distributed Applications

Abstract

Distributed applications that share dynamically changing state are increasingly being deployed in wide-area environments. Such applications must access the state in a consistent manner, but the consistency requirements vary significantly from other systems. For example, shared memory models such as sequential consistency focus on the ordering of operations and the same level of consistency is provided to each process. In interactive distributed applications, the timeliness of updates becoming effective could be an extremely important consistency requirement and it could be different across different users. We propose a system that provides both non-timed and time sensitive read and write operations for manipulating dynamic shared state. For example, a timed read can be used by a process to read a recently written value whereas a timed write can make a new value available to all readers within a certain amount of time. We develop a consistency model that precisely defines the semantics of timed and non-timed read and write operations. A protocol that implements this model is also presented. We also describe an implementation and some performance measurements.