Reducing the cost of group communication with semantic view synchrony

View synchrony (VS) is a powerful abstraction in the design and implementation of dependable distributed systems. By ensuring that processes deliver the same set of messages in each view, it allows them to maintain consistency across membership changes. However experience indicates that it is hard to combine strong reliability guarantees as offered by VS with stable high performance. In this paper we propose a novel abstraction, semantic view synchrony (SVS), that exploits the application's semantics to cope with high throughput applications. This is achieved by allowing some messages to be dropped while still preserving consistency when new views are installed. Thus, SVS inherits the elegance of view synchronous communication. The paper describes how SVS can be implemented and illustrates its usefulness in the context of distributed multi-player games.