Decentralized naming in distributed computer systems

Designing a global character-string naming facility is an important and difficult problem in distributed systems. Providing global names--names that have the same meaning on any participating machine--is a vital step in welding a collection of individual computers into a single, coherent system. But the nature of large distributed systems makes it difficult to implement global naming with acceptable efficiency, fault tolerance, and security: network communication is costly, system components can fail independently, and parts of the system may belong to many autonomous and mutually-suspicious groups. Existing name service designs do not solve the problem in full; even the best current designs do not have the efficiency or capacity to name every object in a large system--they generally name only hosts or mailboxes, not files. This thesis introduces a new paradigm for name service called decentralized naming. Directories at different levels of the global naming hierarchy are implemented using different techniques. The uppermost (global) level employs conventional distributed name servers for scalability, while at lower (regional and local) levels, naming is handled directly by the managers of the named objects. The name mapping protocol uses multicast for fault tolerance and a specialized caching technique for efficiency. A capability system provides security against counterfeit replies to name lookup requests. The multicast name mapping technique is shown to have optimum resiliency, in the sense that whenever an object is accessible at all, it is accessible by name. An analytical model of cache performance is presented, is validated by comparison with measurements on a prototype implementation, and is used to set a limit on how large directories can grow before they must be treated as global rather than regional. The capability scheme is also analyzed: although it reduces both the efficiency and resiliency of name lookup, its impact can be made as small as desired by limiting the frequency with which security policy is allowed to change.

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