Approximate algorithms for document placement in distributed Web servers

We study approximate algorithms for placing a set of documents into M distributed Web servers in this paper. We define the load of a server to be the summation of loads induced by all documents stored. The size of a server is defined in a similar manner. We propose five algorithms. Algorithm 1 balances the loads and sizes of the servers by limiting the loads to k_l and the sizes to k_s times their optimal values, where 1/k_l-1 + 1/k_n-1. This result improves the bounds on load and size of servers in (L.C. Chen et al., 2001). Algorithm 2 further reduces the load bound on each server by using partial document replication, and algorithm 3 by sorting. Algorithm 4 employs both partial replication and sorting. Last, without using sorting and replication, we give algorithm 5 for the dynamic placement at the cost of a factor Q(log M) in the time-complexity.