Serializability is the traditional consistency criterion when shared objects are accessed concurrently. Its main drawback lies in the strong synchronization constraints it imposes on execution of applications when they are run on distributed systems. In this paper we examine weaker consistency criteria for computations in which accesses to shared objects are grouped to form transactions. In particular, we explore causal consistency and causal serializability for transaction based computations. These criteria turn out to be sufficient for a class of applications (e.g., collaborative applications) and their implementation results in greater availability of data and improved performance. These criteria are formally defined and protocols implementing them are presented. We demonstrate that causal consistency allows both read and update transactions to be executed in a wait-free manner. Although write accesses in causal serializability require synchronization with other nodes, read access...

The contributions of this paper are twofold. First, a general method to support fault tolerance for token-based synchronization protocols in distributed systems is introduced. Contrary to traditional approaches, this new method uses a decentralized approach to recover from node failures under fail-stop conditions. Neither does it require a centralized manager nor broadcast support. Second, the method is demonstrated by adopting the protocol for mutual exclusion by Naimi et al. [21] to tolerate faults. An implementation of the new protocol in a distributed execution environment provides fault detection with fault recovery and false alarm detection. Experiments with different fault injection scenarios underline the feasibility of this new approach. Measurements indicate that our protocol inflicts no overhead in the absence of faults and a factor 5 to 10 overhead in the presence of faults. 1. Introduction Executing in a distributed environment requires synchronization to coordinate pha...

www.elsevier.com/locate/jpdc A priority-based distributed group mutual exclusion algorithm when group access is non-uniform �