Cronus [l-7] is an object oriented distibuted system which operates in a heterogeneous computer environment of interconnected local area networks. As a distributed system architecture, Cronus faces a number of resource management issues not present in non-distributed architectures. Stmtegies for effectively conuolling the redundancy and reconfigurability inherent in Cronus are needed to take advantage of the distributed system environment. These strategies for resource management are often conveniently separated into policies and mechanisms. A policy is a goal or guideline set by a system administrator or component designer constraining the decisions made by a resource allocator. A mechanism is an internal system structure designed to implement a class of policies.In the Cronus distributed system model, there are currently two general aspects of resource allocation mechanisms which are particular to the network environment and must be effectively managed. One of these is the binding of a client request to a pticular resource manager for those resources which are available redundantly. Redundancy comes in two forms: replicated objects, (e.g., a mu© file) and replicated managers (any manager for a type can create a new instance of that object type). For both forms the selection of an object manager to provide the given service is an important resource management policy decision. The other important aspect of resource management mechanism is the ability to reconfigure parts of the system by dynamically migrating objects. Object migration is a powerful tool &or matching system resources to tasks in a manner that attempts to maximize some measure of system performance, reliability, or survivability, Both static reconfiguration (e.g., choosing or amending the placement of object managers and their associated objects), and dynamic recontiguration (e.g., movmg an individual object in direct response to demand for its use possible in the Cronus architecture and design.Cmnus development has been suppoltcd by the Rome Air Dwelopment Center, under contracts F30602-81-C-0132 and F30602.84-C-0171,The general approach to resource management in Cronus is to individually control the management of the classes of objects which make up the system. This approach extends Cronus resource management concepts beyond system resources to the abstract resources developed by applications. Resource management for an individual abstract resource (type) and for groups of related resource types (services) in G-onus is based on combining a number of carefully planned mechanisms which are part of the system architecture. In addition to resource management by resource type, a client specific policy which considers collections of object types used in a specific context can be constructed.In Cronus we achieve system wide and easily controllable resource management by requiring the object managers to cooperate in enforcing a resource management policy for their resource type. An object manager can redirect operations to a peer manager on another ...
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