Load Balancing Schemes for a Hierarchical Peer-to-Peer File Search System

Recently, Qin et al. proposed a three-tier Peer-to-Peer (P2P) architecture for real-time file search in distributed networks [8]. In this architecture, indices of files held by the user peers in the bottom layer are stored at the super-peers in the middle layer, and the correlation of those two bottom layers is controlled by the central server(s) in the top layer using the notion of tags. In Qin's system, a heavily loaded super-peer can move excessive load to a lightly loaded super-peer by using a notion of task migration. However, such task migration approach is not sufficient to balance the load of super-peers if the size of tasks is highly imbalanced. To overcome such issue, in this paper, we propose two load-balancing schemes for this architecture, aiming to ensure an even load distribution over the super-peers. The first scheme controls the load of each task in order to decrease the total cost of task migration. The second scheme directly balances the load over tasks by reordering the priority of tags used in the query forwarding step. The effectiveness of the proposed schemes are evaluated by simulation. The result of simulations indicates that all the schemes can work in coordinate, in alleviating the bottleneck situation of super-peers.