Maintaining Consistency in Distributed Systems

Abstract

How should distributed systems preserve consistency in the presence of concurrency and failures? For systems designed as assemblies of independently developed components, concurrent access to data or data structures would normally arise within individual programs, and be controlled using mutual exclusion constructs, such as semaphores and monitors. Where data is persistent and/or sets of operations are related to one another, transactions or linearizability may be more appropriate. Systems that incorporate cooperative styles of distributed execution often replicate or distribute data within groups of components. In these cases, group-oriented consistency properties must be maintained, and tools based on the virtual synchrony execution model greatly simplify the task confronting an application developer. All three styles of distributed computing are likely to be seen in future systems - often, within the same application. This leads us to propose an integrated approach that permits applications that use virtual synchrony to with concurrent objects that respect a linearizability constraint, and vice versa. Transactional subsystems are treated as a special case of linearizability. Keywords and phrases: Transaction, atomicity, monitors, serializability, linearizability, virtual synchrony, object-oriented programming, distributed computing, federated databases, fault-tolerance.