On the inapproximability of M/G/K: why two moments of job size distribution are not enough

@article{Gupta2010OnTI,
  title={On the inapproximability of M/G/K: why two moments of job size distribution are not enough},
  author={Varun Gupta and Mor Harchol-Balter and Jim G. Dai and Bert Zwart},
  journal={Queueing Systems},
  year={2010},
  volume={64},
  pages={5-48}
}
The M/G/K queueing system is one of the oldest models for multiserver systems and has been the topic of performance papers for almost half a century. However, even now, only coarse approximations exist for its mean waiting time. All the closed-form (nonnumerical) approximations in the literature are based on (at most) the first two moments of the job size distribution. In this paper we prove that no approximation based on only the first two moments can be accurate for all job size distributions… 
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