In offline scheduling models, jobs are given with their exact processing times. In their online counterparts, jobs arrive in sequence together with their processing times and the scheduler makes irrevocable decisions ...
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In offline scheduling models, jobs are given with their exact processing times. In their online counterparts, jobs arrive in sequence together with their processing times and the scheduler makes irrevocable decisions on how to execute each of them upon its arrival. We consider a semi-online variant which has equally rich application background, called scheduling with testing, where the exact processing time of a job is revealed only after a required testing operation is finished, or otherwise the job has to be executed for a given possibly over-estimated length of time. For multiprocessor scheduling with testing to minimize the total job completion time, we present several first approximation algorithms with constant competitive ratios for various settings, including a 2 phi-competitive algorithm for the non-preemptive general testing case and a (0.0382 +2.7925(1- 1/2m ))-competitive randomized algorithm, when the number of root machines m > 37 or otherwise 2.7925-competitive, where phi = (1+ 5)/2 < 1.6181 is the golden ratio and m is the number of machines, a (3.5 - 2 3m )-competitive algorithm allowing job preemption when m > 3 or otherwise 3-competitive, and a (phi + phi+1 2 (1 - 1m))-competitive algorithm for the non-preemptive uniform testing case when m > 5 or otherwise (phi + 1)-competitive. Our results improve three previous best approximation algorithms for the single machine scheduling with testing problems, respectively.
Multiprocessor scheduling, also called scheduling on parallel identical machines to minimize the makespan, is a classic optimization problem which has been extensively studied. scheduling with testing is an online var...
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Multiprocessor scheduling, also called scheduling on parallel identical machines to minimize the makespan, is a classic optimization problem which has been extensively studied. scheduling with testing is an online variant, where the processing time of a job is revealed by an extra test operation, otherwise the job has to be executed for a given upper bound on the processing time. Albers and Eckl recently studied the multiprocessor scheduling with testing;among others, for the non-preemptive setting they presented an approximation algorithm with competitive ratio approaching 3.1016 when the number of machines tends to infinity and an improved approximation algorithm with competitive ratio approaching 3 when all test operations take one unit of time each. We propose to first sort the jobs into non-increasing order of the minimum value between the upper bound and the testing time, then partition the jobs into three groups and process them group by group according to the sorted job order. We show that our algorithm achieves better competitive ratios, which approach 2.9513 when the number of machines tends to infinity in the general case;when all test operations each takes one time unit, our algorithm achieves even better competitive ratios approaching 2.8081.
Multiprocessor scheduling, also called scheduling on parallel identical machines to minimize the makespan, is a classic optimization problem that has received numerous studies. scheduling with testing is an online var...
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ISBN:
(纸本)9783030970994;9783030970987
Multiprocessor scheduling, also called scheduling on parallel identical machines to minimize the makespan, is a classic optimization problem that has received numerous studies. scheduling with testing is an online variant where the processing time of a job is revealed by an extra test operation, or otherwise the job has to be executed for a given upper bound on the processing time. Albers and Eckl recently studied the multiprocessor scheduling with testing;among others, for the non-preemptive setting they presented an approximation algorithm with competitive ratio approaching 3.1016 when the number of machines tends to infinity and an improved approximation algorithm with competitive ratio approaching 3 when all test operations take a time unit. We propose to first sort the jobs into the non-increasing order of the minimum value between the upper bound and the testing time, then partition the jobs into three groups and process them group by group according to the sorted job order. We show that our algorithm achieves improved competitive ratios, which approach 2.9513 when the number of machines tends to infinity in the general case;when all test operations take a time unit, our algorithm achieves even better competitive ratios approaching 2.8081.
In the context of decision making under explorable uncertainty, scheduling with testing is a powerful technique used in the management of computer systems to improve performance via better job-dispatching decisions. U...
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In the context of decision making under explorable uncertainty, scheduling with testing is a powerful technique used in the management of computer systems to improve performance via better job-dispatching decisions. Upon job arrival, a scheduler may run some testing algorithm against the job to extract some information about its structure, e.g., its size, and properly classify it. The acquisition of such knowledge comes with a cost because the testing algorithm delays the dispatching decisions, though this is under control. In this article, we analyze the impact of such extra cost in a load balancing setting by investigating the following questions: does it really pay off to test jobs? If so, under which conditions? Under mild assumptions connecting the information extracted by the testing algorithm in relationship with its running time, we show that whether scheduling with testing brings a performance degradation or improvement strongly depends on the traffic conditions, system size and the coefficient of variation of job sizes. Thus, the general answer to the above questions is non-trivial and some care should be considered when deploying a testing policy. Our results are achieved by proposing a load balancing model for scheduling with testing that we analyze in two limiting regimes. When the number of servers grows to infinity in proportion to the network demand, we show that job-size testing actually degrades performance unless short jobs can be predicted reliably almost instantaneously and the network load is sufficiently high. When the coefficient of variation of job sizes grows to infinity, we construct testing policies inducing an arbitrarily large performance gain with respect to running jobs untested.
This thesis focuses on the two machine flow shop problem with unknown delays. This a problem often found in the design of manufacturing facilities, where the equipment can be ordered only after its specifications are ...
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This thesis focuses on the two machine flow shop problem with unknown delays. This a problem often found in the design of manufacturing facilities, where the equipment can be ordered only after its specifications are known with one-hundred-percent confidence. In this industry, the man- agement uses the approach of Critical Path Method (CPM), which, given the stochastic nature of the problem, can lead to undesired prolongation of the project duration. For this reason, the idea of testing some of the jobs is proposed as an exploration through exploitation concept.
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