On programming with view synchrony

View synchrony has been proposed as a programming paradigm for developing reliable distributed applications. The paradigm is particularly attractive when the underlying computing system is asynchronous and prone to complex failure scenarios including partitions. View synchrony en-courages a programming style where groups of processes cooperate closely in order to maintain some form of shared state among them. In this paper, we examine the technical problems that arise in shared state management when pro-gramming applications using view synchrony. We identify three classes of problems corresponding to state transfer upon group joins, state recreation after total failures and state merging after partition unions. We argue that shared state problems are inherent to any implementation,andwith-out explicit support, attempts to solve them may easily ob-scure much of the simplicity and elegance of view synchrony. Finally, we propose an extension to the traditional view syn-chrony model based on the notion of subviews that addresses the problems raised by shared state management. 1