An Adaptive-Priority Queue

  • H. G. Badr
  • I. Mitrani
  • J. R. Spirn
Part of the Progress in Computer Science book series (PCS, volume 3)


Priority scheduling is used frequently in computer systems; however, such schedules usually have a “fail-safe” provision to prevent high-priority requests from causing unlimited delay to low-priority ones. In this paper, a queue and server is considered which has two sources of Poisson-arrival customers, types a and b respectively. Non-preemptive priority is granted to type a customers, except that whenever the number of waiting type b customers exceeds a specified threshold, class b receives priority. Service times are assumed exponentially distributed with a common mean, but it is possible to greatly relax this restriction. The intent is to grant priority to class a most of the time, while bounding the mean waiting time of class b customers under heavy class a load. This particular fail-safe mechanism is shown to have the property that for system states in which class b is below the threshold, the occupancy probability is exactly the same as if class a always had high priority.


Service Time Queue Length Busy Period Priority Schedule State Transition Diagram 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


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  1. 1.
    Although the characterization is not complete in as much as the class of customer currently in service is unknown, it is sufficient to permit an analysis to be undertaken.Google Scholar
  2. 2.
    Recall that P(I) is not included in transform P(y, z).Google Scholar

Copyright information

© Springer Science+Business Media New York 1982

Authors and Affiliations

  • H. G. Badr
    • 1
  • I. Mitrani
    • 2
  • J. R. Spirn
    • 3
  1. 1.Department of Computer ScienceSUNY at Stony BrookStony BrookUSA
  2. 2.Computing LaboratoryThe University of NewcastleNewcastle upon TyneUnited Kingdom
  3. 3.Digital Equipment CorporationMaynardUSA

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