The wandering token: Congestion avoidance of a shared resource

In a distributed system where scalability is an issue, the problem of enforcing mutual exclusion often arises in a soft form: the infrequent failure of the mutual exclusion predicate is tolerated, without compromising the consistent operation of the overall system. For instance this occurs when the operation subject to mutual exclusion requires massive use of a shared resource. We introduce a scalable soft mutual exclusion algorithm, based on token passing: one distinguished feature of our algorithm is that instead of introducing an overlay topology we adopt a random walk approach. The consistency of our proposal is evaluated by simulation, and we exemplify its use in the coordination of large data transfers in a backbone based network. This algorithm is studied in the frame of the CoreGRID Institute of Grid Information, Resource and Workflow Monitoring Services, in cooperation with the FORTH Institute, in Greece.