Consistent Key Mapping in Structured Overlays

Abstract

Most structured peer-to-peer overlays rely on consistent hashing to determine the node that is responsible for a given key. For consistent hashing to work properly, it is necessary that the nodes have a consistent view of their neighborhood in the identifier space. However, if routing anomalies occur in the underlying network, this view can become inconsistent, causing unstable overlay behavior and, worse, allowing more than one node to assume responsibility for ranges of keys. We present a set of techniques for preventing inconsistencies under routing anomalies, and we propose to adopt strategies from mobile ad-hoc networking for maintaining connectivity in the presence of path failures. We evaluate our design in the context of Pastry and present results from a deployment in the PlanetLab testbed.