Extending Pastry by an Alphanumerical Overlay

Many load balancing strategies have been proposed for distributed hash tables, like Pastry. These strategies assume that hash functions spread even skewed key distributions almost evenly over the ID space. They neglect the problem that many applications produce data with common keys (multi-sets) that entail hash collisions and therewith load imbalance concerning query and storage load. A second drawback of using hash functions in DHTs is the lack of range queries needed in many scenarios. This paper presents a solution for how to use the routing structure of the P2P network Pastry to create a new alphanumerical overlay with very little additional costs. This overlay is capable of storing data in a totally ordered manner instead of using hashed keys. Therewith, it enables range queries and sophisticated load balancing. We discuss the impact on Pastry that arises when nodes are relocated during load balancing. This possibly causes a skewed distribution of nodes in the circular id space. We demonstrate the feasibility of our idea including advantages and problems through an evaluation of simulations.