Multi-Server Queueing Systems with Multiple Priority Classes

  • Authors:
  • Mor Harchol-Balter;Takayuki Osogami;Alan Scheller-Wolf;Adam Wierman

  • Affiliations:
  • Department of Computer Science, Carnegie Mellon University, Pittsburgh 15213;Department of Computer Science, Carnegie Mellon University, Pittsburgh 15213;Tepper School of Business, Carnegie Mellon University, Pittsburgh 15213;Department of Computer Science, Carnegie Mellon University, Pittsburgh 15213

  • Venue:
  • Queueing Systems: Theory and Applications
  • Year:
  • 2005

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Abstract

We present the first near-exact analysis of an M/PH/k queue with m 2 preemptive-resume priority classes. Our analysis introduces a new technique, which we refer to as Recursive Dimensionality Reduction (RDR). The key idea in RDR is that the m-dimensionally infinite Markov chain, representing the m class state space, is recursively reduced to a 1-dimensionally infinite Markov chain, that is easily and quickly solved. RDR involves no truncation and results in only small inaccuracy when compared with simulation, for a wide range of loads and variability in the job size distribution.Our analytic methods are then used to derive insights on how multi-server systems with prioritization compare with their single server counterparts with respect to response time. Multi-server systems are also compared with single server systems with respect to the effect of different prioritization schemes--"smart" prioritization (giving priority to the smaller jobs) versus "stupid" prioritization (giving priority to the larger jobs). We also study the effect of approximating m class performance by collapsing the m classes into just two classes.