A name service for evolving, heterogeneous systems

Abstract

This paper describes a name service designed for long term use in a continually evolving heterogeneous system. There are two conflicting goals for a name service in this environment: to ease the task of dealing with the distribution and heterogeneity by providing a uniform service throughout the system that masks these characteristics as much as possible, and to keep software development and maintenance costs manageable when faced with the frequent introduction of new system types. A single name service implemented across all system types, which would be an appropriate choice given the first goal alone, is infeasible when the second goal is considered. In attempting to satisfy these conflicting goals we have designed a software structure that allows the efficient integration of existing heterogeneous implementations of the same generic service. In the specific case of the name service, this allows us to build a global service that makes use of, rather than replaces, the name services of the component subsystems. This approach has a number of desirable properties. For one, the system is scalable, since the processing load is naturally distributed among the subsystems. Second, applications existing in newly introduced subsystems can continue to run unaltered, while the modifications they make in their local name services are automatically reflected in the global name service. This is an important attribute in environments where it is impossible or too expensive to modify all existing application and system code. Finally, our design allows wide latitude in the degree to which an individual subsystem type is incorporated; an amount of integration effort appropriate to the benefits received can be chosen individually for each subsystem type as it is introduced. A prototype implementation has been built as part of the Heterogeneous Computer Systems project at the University of Washington. This service supports RPC binding and other applications in our heterogeneous environment Measurements of the performance of this prototype show that it is close to that of the underlying name services, due largely to the use of specialized caching techniques.