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Server Allocation in Grid Systems with On/Off Sources
 in: Proceedings of ISPA 2006 Workshops, Lecture Notes in Computing Science
, 2006
"... Abstract. A system consisting of a number of servers, where demands of different types arrive in bursts (modelled by interrupted Poisson processes), is examined in the steady state. The problem is to decide how many servers to allocate to each job type, so as to minimize a cost function expressed in ..."
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Abstract. A system consisting of a number of servers, where demands of different types arrive in bursts (modelled by interrupted Poisson processes), is examined in the steady state. The problem is to decide how many servers to allocate to each job type, so as to minimize a cost function expressed in terms of average queue sizes. First, an exact analysis is provided for an isolated IP/M/n queue. The results are used to compute the optimal static server allocation policy. The latter is then compared to two heuristic policies which employ dynamic switching of servers from one queue to another (such switches take time and hence incur costs). 1
Dynamic Operating Policies for Commercial Hosting Environments
 5th UK eScience All Hands Meeting
, 2006
"... This paper reports on two strands of work that are being undertaken as part of the EPSRC funded DOPCHE project. The paper focuses on open software architectures for dynamic operating policies and a performance model used to nd optimal operating policies. 1 ..."
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This paper reports on two strands of work that are being undertaken as part of the EPSRC funded DOPCHE project. The paper focuses on open software architectures for dynamic operating policies and a performance model used to nd optimal operating policies. 1
Monotonicity Of Optimal Performance Measures For Polling Systems
 Probability in the Engineering and Informational Sciences
, 1997
"... We consider scheduling a single server in a multiclass queue subject to setup times and setup costs. We examine the issue of whether or not reductions in the mean and variance of the setup time distributions can lead to degraded system performance. Provided that setups are reduced according ..."
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We consider scheduling a single server in a multiclass queue subject to setup times and setup costs. We examine the issue of whether or not reductions in the mean and variance of the setup time distributions can lead to degraded system performance. Provided that setups are reduced according to a stochastically smaller ordering, we show that if an optimal policy is used both for the original system as well as for the system with reduced setup times, then an improvement in performance is guaranteed. Even in cases for which a truly optimal policy is unknown, idling can be employed to avoid degradation of performance as setup times are cut. We extend this approach to show that system performance is monotonic with respect to service time distributions, switching costs, holding costs, and uniform reductions in the arrival rates. Extensions to sequencedependent setups and job feedback are noted. 1. Introduction We consider the problem of scheduling a single server in a mul...
Beyond the cµ Rule: Dynamic Scheduling Of A TwoClass Loss Queue
, 1997
"... We consider scheduling a single server in a twoclass M/M/1 queueing system with finite buffers subject to holding costs and rejection costs for rejected jobs. We use dynamic programming to investigate the structural properties of optimal policies. Provided that the delay of serving a job is alwa ..."
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We consider scheduling a single server in a twoclass M/M/1 queueing system with finite buffers subject to holding costs and rejection costs for rejected jobs. We use dynamic programming to investigate the structural properties of optimal policies. Provided that the delay of serving a job is always less costly than rejecting an arrival, we show that the optimal policy has a monotonic threshold type of switching curve; otherwise, numerical analysis indicates that the threshold structure may not be optimal.
Optimal service policies under learning effects
 International Journal of Services and Operations Management
, 2008
"... Abstract: For highvalue workforces in service organisations such as call centres, scheduling rules rely increasingly on queueing system models to achieve optimal performance. Most of these models assume a homogeneous population of servers, or at least a static service capacity per service agent. In ..."
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Abstract: For highvalue workforces in service organisations such as call centres, scheduling rules rely increasingly on queueing system models to achieve optimal performance. Most of these models assume a homogeneous population of servers, or at least a static service capacity per service agent. In this work we examine the challenge posed by dynamically fluctuating service capacity, where servers may increase their own service efficiency through experience; they may also decrease it through absence. We analyse the special case of a single agent selecting between two different job classes, and examine which of five service allocation policies performs best in the presence of learning and forgetting effects. We find that a type of specialisation minimises the steady state queue size; crosstraining boosts system capacity the most; and no simple policy matches a dynamic optimal cost policy under all conditions.
To my parents To Louiseiii Acknowledgements
, 2009
"... First and foremost I’d like to thank my joint supervisors: Dr. Nigel Thomas and Prof. Isi Mitrani. You have given me invaluable advice and guidance even though I was sometimes too stubborn to follow it! This thesis owes much to the threeandahalf years of patient supervision you have both given me ..."
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First and foremost I’d like to thank my joint supervisors: Dr. Nigel Thomas and Prof. Isi Mitrani. You have given me invaluable advice and guidance even though I was sometimes too stubborn to follow it! This thesis owes much to the threeandahalf years of patient supervision you have both given me. But perhaps more importantly, I, as an academic and a human, owe much to that supervision too. Secondly I’d like to thank my examiners: Will Knottenbelt of Imperial College London and Aad van Moorsel for a very enjoyable viva and interesting comments. Many thanks also go to Chris Smith for our discussions about this and related work. As well as the necessary occasional drink and laugh. I’d also like to thank everyone at Warwick University involved in the ‘Dynamic Operating Policies
Optimal Scheduling of Queueing Networks with Switching Times Using Genetic Algorithms
"... Abstract: in this paper we consider the problem of optimal scheduling of queueing networks with switching times based on genetic algorithms approach. We propose a special chromosome encoding scheme, crossover and mutation operators. Deterministic mutation is used to prevent premature convergence to ..."
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Abstract: in this paper we consider the problem of optimal scheduling of queueing networks with switching times based on genetic algorithms approach. We propose a special chromosome encoding scheme, crossover and mutation operators. Deterministic mutation is used to prevent premature convergence to a poor solution. Finally, results of computational experiments are included to compare deterministic mutation with classical probabilistic one. KeyWords: queueing networks; optimal scheduling; switching times; genetic algorithms; deterministic mutation. 1
Added entries UNIVERSITY OF NEWCASTLE UPON TYNE
, 2006
"... erver allocation in Grid systems with on/off sources ..."
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Finitecapacity Multiclass Production Scheduling with Setup Times
, 1998
"... We treat the scheduling of a single server in a finitebuffer capacity, multiclass, maketoorder production system subject to inventory holding costs, setup times, and customer rejection costs. We employ theoretical and numerical analysis of a Markov decision process model to investigate the stru ..."
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We treat the scheduling of a single server in a finitebuffer capacity, multiclass, maketoorder production system subject to inventory holding costs, setup times, and customer rejection costs. We employ theoretical and numerical analysis of a Markov decision process model to investigate the structure of optimal policies and the performance of heuristic policies. We establish the monotonicity of optimal performance with respect to the system parameters. Based on our insights, we provide a heuristic policy called the Capacitated Modified Index Rule (CMIR) for capacitated scheduling with customer loss penalties. The CMIR heuristic can easily be precomputed and stored for realtime control. Numerical benchmarking with respect to the optimal performance as well as an existing heuristic suggests that CMIR is very effective. Keywords: Polling system; Finite buffer; Capacitated production scheduling; Markov decision process model; Nearoptimal heuristic scheduling 1. Introduction We foc...