Providing Persistent Objects in Distributed Systems

THOR is a persistent object store that provides a powerful programming model. THOR ensures that persistent objects are accessed only by calling their methods and it supports atomic transactions. The result is a system that allows applications to share objects safely across both space and time. The paper describes how the THOR implementation is able to support this powerful model and yet achieve good performance, even in a wide-area, large-scale distributed environment. It describes the techniques used in THOR to meet the challenge of providing good performance in spite of the need to manage very large numbers of very small objects. In addition, the paper puts the performance of THOR in perspective by showing that it substantially outperforms a system based on memory mapped files, even though that system provides much less functionality than THOR.