Foundations for Highly Available Content-Based Publish/Subscribe Overlays

Content-based publish/subscribe overlays offer a scalable messaging substrate for various event-based distributed systems. In an enterprise environment where service level agreements(SLAs) are strictly enforced, maintaining high availability and efficiency of the broker overlay is critical. To support these requirements, a set of three primitive operations are proposed to allow arbitrary transformations of an overlay to an optima lone, and two additional primitives are developed to enable ondemand adjustments when there are permanent or transient failures. Both sets of primitive operations minimize disruption by preserving message delivery guarantees even as the overlay topology changes, requiring no overhead when the overlay is not being modified, operating on a fixed neighborhood of brokers regardless of the size of the overlay, and completing quickly under a variety of conditions.