Bayou is a replicated, weakly consistent storage system designed for a mobile computing environment that includes portable machines with less than ideal network connectivity. To maximize availability, users can read and write any accessible replica. Bayou's design has focused on supporting apphcation-specific mechanisms to detect and resolve the update conflicts that naturally arise in such a system, ensuring that replicas move towards eventual consistency, and defining a protocol by which the resolution of update conflicts stabilizes. It includes novel methods for conflict detection, called dependency checks, and per-write conflict resolution based on client-provided merge procedures. To guarantee eventual consistency, Bayou servers must be able to rollback the effects of previously executed writes and redo them according to a global senalization order. Furthermore, Bayou permits clients to observe the results of all writes received by a server, Including tentative writes whose conflicts have not been ultimately resolved. This paper presents the motivation for and design of these mechanisms and describes the experiences gained with an initial implementation of the system.

. 1 Rumor is an optimistically replicated file system designed for use in mobile computers. Rumor uses a peer model that allows opportunistic update propagation among any sites replicating files. The paper outlines basic characteristics of replication systems for mobile computers, describes the design and implementation of the Rumor file system, and presents performance data for Rumor. The research described demonstrates the feasibility of using peer optimistic replication to support mobile computing. 1 Introduction Mobile computers typically suffer from weaker connectivity than that enjoyed by wired machines. Latencies are significantly higher, bandwidth is limited, power conservation requirements discourage communication, some communications media cost money to use, and long-duration disconnections are the norm. In this context, data management techniques that dramatically reduce the need for continuous connectivity are highly desirable. One such potential class of solutions is da...

Mobile computers often suffer from limited connectivity, or even complete lack of network access. Moreover, in wireless networks some machines are often more accessible to mobile computers than others are. Ideally, nomadic users want the same quality and speed of database access as when they are well connected to the network. Replicated databases meet this need by allowing each mobile machine to carry its own copy of key data. But existing replicated systems are not well suited for all nomadic scenarios. Certain important mobile computing situations require optimistic peer-oriented database replication. The Bengal Database Replication System has these characteristics and was designed to operate in difficult nomadic conditions. This paper presents the design assumptions of the system, describes its architecture, presents performance data on its operation, and discusses future enhancements for the system. The paper also contrasts the system to other replicated databases, concentrating on their suitability for nomadic computing. The Bengal technology can play an important role in the development of highly scalable, highly available, fault-tolerant database systems. Keywords: distributed, optimistic, database, replication, peer-to-peer 1.

Mobile computing and workgroup computing are emerging technologies which have so far been treated independently. Current approaches to support cooperative work neglect the special characteristics of mobile environments like limited bandwidth or temporary disconnection. On the other hand, approaches to support disconnected operation in mobile environments rely on the assumption that the degree of data-sharing is low which is obviously not appropriate for cooperative work. In this paper, we utilize the COACT cooperative transaction model [25, 31, 19] to provide support for parallel, disconnected activities. The model incorporates the notion of resolvable, simultaneous work. We show how the COACT merge algorithm reduces conflicts by exploiting operation semantics and offering consistent sequences of operations. We believe that our new approach is a viable solution to the growing demand for cooperation in mobile environments. 1 Introduction The global information infrastructure --- open ...

Mobile computing and workgroup computing are emerging technologies whichhave so far been treated independently. Current approaches to support cooperative work neglect the special characteristics of mobile environments like limited bandwidth or temporary disconnection. On the other hand, approaches to support disconnected operation rely on the assumption that the degree of data-sharing is lowwhichisobviously not appropriate for cooperative work. In this paper, we utilize the CoAct cooperative transaction model to provide support for parallel activities in mobile environments. We present a system architecture that is able to cope with the special characteristics of mobile environments and a formal framework for the consistent information exchange between mobile users. The paper shows howtheCoAct history merge algorithm reduces conflicts by exploiting operation semantics and offering consistent sequences of operations. We believe that our new approach is a viable solution to th...