Daniel L. McCue

Maintaining information about persistent replicated objects in a distributed system

Presents a general model for persistent replicated object management and identify what metainformation about objects needs to be maintained by a naming and binding service to ensure that objects named by application programs are bound to only those object replicas which are in a mutually consistent state. These ideas are developed within the framework of a distributed system in which application programs are composed of atomic actions (atomic transactions) manipulating persistent (long-lived) objects.<<ETX>>

The Replica Management System: a scheme for flexible and dynamic replication

The actual gains achieved by replication are a complex function of the number of replicas, the placement of those replicas, the replication protocol, the nature of the transactions performed on the replicas, and the availability and performance characteristics of the machines and networks composing the system. This paper describes the design and implementation of the Replica Management System, which allows a programmer to specify the quality of service required for replica groups in terms of availability and performance. From the quality of service specification, information about the replication protocol to be used, and data about the characteristics of the underlying distributed system, the RMS computes an initial placement and replication level. As machines and communications systems are detected to have failed or recovered, or performance characteristics change, the RMS can be re-invoked to compute an updated mapping of replicas which preserves the desired quality of service. The result is a flexible, dynamic and dependable replication system.<<ETX>>

Structuring fault-tolerant object systems for modularity in a distributed environment

The object-oriented approach to system structuring has found widespread acceptance among designers and developers of robust computing systems. The authors propose a system structure for distributed programming systems that support persistent objects and describe how properties such as persistence and recoverability can be implemented. The proposed structure is modular, permitting easy exploitation of any distributed computing facilities provided by the underlying system. An existing system constructed according to the principles espoused here is examined to illustrate the practical utility of the proposed approach to system structuring. >

Computing replica placement in distributed systems

The authors investigate the design of a replica management system (RMS) which allows a programmer to specify the quality of service required for individual replicated objects in terms of availability and performance. From the quality of service specification, information about the replication protocol to be used, and data about the characteristics of the underlying distributed system, the RMS computes an initial placement and replication level for the object. As machines and communications systems are detected to have failed or recovered, the RMS can be reinvoked to compute an updated mapping of replicas which preserves the desired quality of service. Preliminary simulation of the authors RMS shows that its placement algorithm gives consistent improvements in the availability of a replicated service than simply placing replicas on nodes at random, as is done in most distributed systems.<<ETX>>

Implementing fault-tolerant object systems on distributed memory multiprocessors

The design and implementation of an object management layer for a distributed memory multiprocessor system is described. It has been used for supporting an object-oriented fault-tolerant system (Arjuna). The authors discuss how various aspects of distribution transparency (location, access, migration, concurrency, replication and failure) have been incorporated in the design.<<ETX>>

Developing a Class Hierarchy for Object-Oriented Transaction Processing

This paper describes the development of a class hierarchy to support distributed transaction processing. Inheritance and polymorphism, key features of the object oriented programming model, have been used to develop a hierarchy of classes which convey to their subclasses the behaviours of persistence, concurrency-control, recoverability and identity necessary for distributed transaction processing. The development is traced from the requirements of distributed transaction processing to the definition of classes supporting these key properties. The system is interesting in both its development and its results. The development, not based on any rigourous design methodology, illustrates some of the design decisions unique to object-oriented systems. The resulting class hierarchy provides a flexible, object-oriented interface for reliable distributed programming. The paper includes a step-by-step description of the design of the classes and the class hierarchy.