Global caching mechanisms in clusters of Web servers

We investigate how to improve Web cluster performance through cooperation protocols for a shared use of the main memories of the server nodes (global caching). Many popular schemes to locate requested documents are based upon locality information sharing (namely, informed cooperation); we also propose a novel approach for document lookup through a query broadcasting mechanism (namely, on-demand cooperation). Moreover, we consider the migration and handoff mechanisms to retrieve successfully located documents. The experimental results show that, in a static Web scenario, the on-demand with handoff scheme performs similarly to the informed with handoff scheme, whereas the on-demand with migration scheme outperforms the informed with migration scheme. On the other hand, in a scenario with some dynamic requests, on-demand cooperation experiences a significant performance degradation with respect to informed cooperation.