Physical Node 1 VAS Memory Swap Persistent Swap Persistent

In large persistent object systems it is possible to have many million (or eventually billion or more) objects in existence. These objects must be managed to enable their eeective and convenient use. At the heart of this management problem is the structure which maintains information about the objects and provides services on the objects using the information it maintains. We refer to this structure as a directory of objects. In a transparently distributed object system the directory must contain entries for all objects in the system regardless of their location. To ensure both eeciency and reliability any implementation of a global directory of objects (GDO) must be done carefully. This paper details the design of a GDO for a fully distributed persistent object system that is currently being built in a single shared address space. The design of the directory ooers eecient, scalable, and reliable services across a distributed environment. Further, although it is designed for a speciic (and somewhat unusual) environment, the implementation ideas are applicable to other distributed object systems. 1 Introduction This paper addresses the issue of managing large collections of persistent objects in a distributed environment. It does this by focusing on the key data structure required for object management, the object directory. Logically a single, global directory of objects (GDO) is desired but this is not a practical implementation strategy. Instead, a carefully distributed data structure is required that provides reliable, eecient, and scalable services while maintaining the appearance of a single directory to its users. The GDO for a persistent object system acts, passively, as a repository for information about the objects being maintained in the system. It also acts, actively, as a provider of management services on those same objects. Depending