Local management of a global resource in a communication network

Abstract

This paper introduces a new distributed data object called Resource Controller that provides an abstraction for managing the consumption of a global resource in a distributed system. Examples of resources that may be managed by such an object include; number of messages sent, number of nodes participating in the protocol, and total CPU time consumed. The Resource Controller object is accessed through a procedure that can be invoked at any node in the network. Before consuming a unit of resource at some node, the controlled algorithm should invoke the procedure at this node, requesting a permit or a rejection. The key characteristics of the Resource Controller object are the constraints that it imposes on the global resource consumption. An ( M, W )-Controller guarantees that the total number of permits granted is at most M ; it also ensures that, if a request is rejected, then at least M—W permits are eventually granted, even if no more requests are made after the rejected one. In this paper, we describe several message and space-efficient implementations of the Resource Controller object. In particular, we present an ( M, W )-Controller whose message complexity is O(n log 2 n log( M/(W + 1)) where n is the total number of nodes. This is in contrast to the O(nM) message complexity of a fully centralized controller which maintains a global counter of the number of granted permits at some distinguished node and relays all the requests to the node.