Load balancing and hot spot relief for hash routing among a collection of proxy caches

Hash routing partitions the entire URL space among a collection of cooperating proxy caches. Each partition is assigned to a cache server. Duplication of cache contents is eliminated. Client requests to a cache server for non-assigned partition objects are forwarded to proper sibling caches. As a result, the load level of the cache servers can be quite unbalanced. We examine an adaptable controlled replication (ACR) of non-assigned partition objects in each cache server to reduce the load imbalance and relieve the problem of hot-spot references. Trace-driven simulations are conducted to study the effectiveness of ACR. The results show that: (1) access skew exists, and the load of the cache servers tends to be unbalanced in hash routing; (2) with a relatively small amount of ACR, say 10% of the cache size, significant improvements in load balance can be achieved; and (3) ACR provides a very effective remedy for load imbalance due to hot-spot references.