Forwarding in the Publiy Distributed Publish / Subscribe System

Fine-grained filtering capabilities of content-based Publish/Subscribe (P/S) overlays often lead to scenarios in which publications pass through brokers with no local matching subscribers. Processing of messages at these pure forwarding brokers amounts to inefficient use of resources and should ideally be avoided. Accomplishing this goal requires a rethought of how the P/S overlays are maintained. In this paper, we develop an approach that largely mitigates this problem by building and adaptively maintaining a highly connected overlay mesh superimposed atop a low connectivity primary overlay network. While the primary overlay network provides basic forwarding routes, the mesh structure provides a rich set of alternative forwarding choices which can be used to bypass pure forwarding brokers. Moreover, the overlay mesh provides unique opportunities for load balancing and congestion avoidance. Through extensive experimental evaluation on a cluster and Planetlab, we compare the performance of our approach with that of conventional P/S algorithms as baseline. Our results indicate that our approach improves publication delivery delay and lowers network traffic while incurring negligible computational and bandwidth overhead. Furthermore, compared to the baseline, we observed significant gains of up to 115% in terms of system throughput.