Replication techniques for speeding up parallel applications on distributed systems

Most methods for programming loosely-coupled systems are based on message-passing. Recently, however, methods have emerged based on ‘‘virtually’ ’ sharing data. These methods simplify distributed programming, but are hard to implement efficiently, as loosely-coupled systems do not contain physical shared memory. We introduce a new model, the shared data-object model, that eases the implementation of parallel applications on loosely-coupled systems, but can still be implemented efficiently. In our model, shared data are encapsulated in passive data-objects, which are variables of userdefined abstract data types. To speed up access to shared data, data objects are replicated. This ability to replicate objects is a significant difference with other object-based models (e.g., Emerald and Amber). Also, by replicating logical objects rather than physical pages, our model has many advantages over shared virtual memory systems. This paper discusses the design choices involved in replicating objects and their effect on performance. Important issues are: how to maintain consistency among different copies of an object; how to implement changes to objects; and which strategy for object replication to use. We have implemented several options to determine which ones are most efficient. 1