Minimum-cost load balancing document distribution in Distributed Web Server systems

Motivated by load balancing on servers in DWS(Distributed Web Server) system, this paper considers the following problem: Given a workload of each web document, a common workload acceptable to all servers, and a cost required to transfer each document to each server, find a document distribution with a minimum total cost required to be transferred satisfying that the total workload of documents on each server does not exceed an acceptable workload when each document is allowed to be placed on multiple servers. In this paper, we prove that this problem is strongly NP-hard even in the case of a unit cost for transfer. Moreover, we present two algorithms for the problem in this case, an approximation one and a greedy one. In particular, the greedy algorithm can be solved in the case of an enough acceptable workload.