Cooperative XPath caching

Motivated by the fact that XML is increasingly being used in distributed applications, we propose building a cooperative caching scheme for XML documents. Our scheme allows sharing cache content among a number of peers. To facilitate sharing, a distributed prefix-based index is built based on the queries whose results are cached. In the loosely-coupled sharing approach, each peer stores in its local cache results of its own queries and just publishes the associated queries to the index. In the tightly-coupled approach, each peer is assigned a specific part of the query space and stores in its local cache the results of the corresponding queries. Both approaches result in a dynamic organization of content that evolves over time based on the query load, the number of peers and the overall storage available. We present a number of associated design choices such as using a DHT for distributing the prefix-based index and a proactive cache replacement policy. We also report on a number of experiments that show the benefits of cooperative caching and highlight the pros and cons of loosely and tightly coupled cache sharing.