Towards Expressive Publish / Subcribe Systems

Abstract

Traditional content based publish/subscribe (pub/sub) systems allow users to express stateless subscriptions evaluated on individual events. However, many applications such as monitoring RSS streams, stock tickers, or management of RFID data streams require the ability to handle stateful subscriptions. In this paper, we introduce Cayuga, a stateful pub/sub system based on nondeterminis- tic finite state automata (NFA). Cayuga allows users to express subscriptions that span multiple events, and it supports powerful language features such as param- eterization and aggregation, which significantly extend the expressive power of standard pub/sub systems. Based on a set of formally defined language opera- tors, the subscription language of Cayuga provides non-ambiguous subscription semantics as well as unique opportunities for optimizations. We experimentally demonstrate that common optimization techniques used in NFA-based systems such as state merging have only limited effectiveness, and we propose novel effi- cient indexing methods to speed up subscription processing. In a thorough exper- imental evaluation we show the efficacy of our approach.