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Algorithms for distributed systems under imperfect status information
Abstract
A recent trend in computer system design has been to distribute the tasks among the multiple processors and a wide variety of computer systems can be proposed. The potential benefits of this trend include modular expansion, increased cost-performance, availability, and reliability. To fully exploit these potential advantages, the efficient control of the resources is essential. In this dissertation, we attack some of important problems which arise in the distributed system environment. Central to this dissertation is the issue of imperfect information, and how to make control decisions in the face of imperfect information. While a great deal of attention has been lavished on token-ring systems over the past few years, little has been said about synthesizing protocols to satisfy complex priority requirements. We present an algorithm that partly fills this gap. It is a simple, adaptive algorithm which can ensure prescribed differential service to the various job classes. Applications include maintaining a throughput differential between job classes, integrating voice and data packets, and maintaining mean waiting times of the various job classes in prescribed ratios. Such an algorithm is likely to be useful whenever disparate traffic classes must coexist on the same ring. We also study the effect of the decay of status information on the goodness of load balancing algorithms. We study empirically the relationship between the characterizing parameters of a very simple model using the join-the-shortest-queue algorithm. This is done using regression analysis. Our results indicate that these parameters--number of queues, status update rate, and coefficient of variation for the job service time--are far from orthogonal in their impact on system performance. We have empirically obtained expressions for the sensitivity of the response time to the characterizing parameters. Designers can use this expression to determine appropriate status update rates. We also present a comparison of some simple distributed load balancing algorithms which update status information regularly with those which do so adaptively. The adaptive algorithms only broadcast status when it changes by more than a threshold. They are almost as simple to implement as algorithms which periodically exchange status information, and provide better performance. Finally, we introduce a simple, adaptive buffer allocation algorithm. We study the performance of an adaptive buffer allocation algorithm in the face of the imperfect status information for the control of distributed systems in which multiple classes of customers contend for a finite buffer which is served by a single server. We believe that this algorithm is especially useful when the number of the classes changes dynamically, or when the input loading changes dynamically. The adaptive algorithm is especially useful when buffer sizes are small.
Subject Area
Computer science|Electrical engineering
Recommended Citation
Choi, Myungwhan, "Algorithms for distributed systems under imperfect status information" (1990). Doctoral Dissertations Available from Proquest. AAI9022673.
https://scholarworks.umass.edu/dissertations/AAI9022673