The Inherent Cost of Strong-Partial View-Synchronous Communication

Process groups and group-based communication have proven to be useful paradigms for structuring reliable applications in distributed systems. The approach is typically realized through view-synchronous communication (VSC) that integrates a reliable multicast facility with a group membership service in the form of view changes. In this paper we examine algorithmic issues associated with VSC group membership in large-scale distributed systems where network partitions may result in multiple views to be active concurrently. We first derive necessary conditions on the partial order of installed views such that VSC is meaningful and solvable in the presence of partitions. We then prove that strong-partial VSC, which guarantees concurrent views to be disjoint, is not easier than atomic commitment. As such, all know lower bound results for atomic commitment are also lower bounds for this problem, including the impossibility of nonblocking solutions in the presence of communication failures. We discuss the practical implications of our results in constructing group communication facilities for large-scale distributed systems.