Consistency-based routing in overlay networks

This paper introduces GRACE – the Global Replication and Consistency Environment – a layered architecture deployed on Distributed Hash Tables (DHT), in which the tension between availability, consistency and performance is mitigated both by providing support for relaxed consistency semantics and by the DHT technology. We describe how the benefits of DHTs, such as scalable lookup and ease of management are inherited at the replication layer. The routing algorithm that provides access to a replica of the required level of consistency extends the traditional routing algorithms in DHTs to take into account consistency information. We provide some optimizations of the basic algorithm, based on the multidimensionality idea, for load balancing and high resiliency. GRACE is currently being tested on top of PlanetLab. A series of applications would benefit from being deployed on GRACE, as we point out in this paper.