Distributed publish/subscribe systems are usually deployed on top of an overlay network that enables complex routing strategies implemented in the application layer. Up to now, only little effort has been spent on the design of the broker overlay network assuming that it is either static or manually administered. As publish/subscribe systems are increasingly targeted at dynamic environments where client behavior and network characteristics vary over time, static overlay networks lead to suboptimal performance. In this paper, we present a self-organizing broker overlay infrastructure that adapts dynamically to achieve a better efficiency on both, the application and the network layer. This is obtained by taking network metrics as well as notification traffic into account.
Most research in the area of publish/subscribe systems has not considered fault-tolerance as a central design issues. However, faults do obviously occur and masking all faults is at least expensive if not impossible. A potential alternative (or sensible supplementation) to fault masking is self-stabilization which allows a system to recover from arbitrary transient faults such as memory perturbations, communication errors, and process crashes with subsequent recoveries. In this paper we discuss how publish/subscribe systems can be made selfstabilizing by using self-stabilizing content-based routing. When the time between consecutive faults is long enough, corrupted parts of the routing tables are removed, while correct parts are refreshed in time, and missing parts are inserted. To judge the efficiency of self-stabilizing content-based routing, we compare it to flooding, which is the naïve implementation of a self-stabilizing publish/subscribe system. We show that our approach is superior to flooding for a large range of practical settings.
Abstract. Recent work on self-stabilizing routing in publish/subscribe systems showed that it is feasible to automate reconfigurations in case of faults by enabling the system to recover from arbitrary transient faults.In this paper, we discuss how to incorporate planned reconfigurations of the broker topology into self-stabilizing publish/subscribe systems without service interruption. We present an algorithm that uses a coloring mechanism to enable the system to be automatically switched from one system configuration to another. The colors thereby synchronize the broker overlay and the publish/subscribe routing layer.
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