Query Routing in the TerraDir Distributed Directory

We present the design and evaluation of the query-routing protocol of the TerraDir distributed directory. TerraDir is a wide-area distributed directory designed for hierarchical namespaces, and provides a lookup service for mapping keys to objects. We introduce distributed lookup and caching algorithms that leverage the underlying data hierarchy. Our algorithms provide efficient lookups while avoiding the load imbalances often associated with hierarchical systems. The TerraDir load balancing scheme also incorporates a node replication algorithm that provides configurable failure resilience with provably low overheads.