Pipelined operator tree scheduling in heterogeneous environments

  • Authors:

  • Arash Termehchi;Mohammad Ghodsi

  • Affiliations:

  • Parallel Processing Laboratory, Department of Computer Engineering, Sharif University of Technology, Tehran, Iran;Parallel Processing Laboratory, Department of Computer Engineering, Sharif University of Technology, Tehran, Iran

  • Venue:
  • Journal of Parallel and Distributed Computing
  • Year:
  • 2003

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Abstract

Pipelined operator tree (POT) scheduling is an important problem in the area of parallel query optimization. A POT is a tree with nodes representing query operators that can run in parallel and edges representing communication between adjacent operators that is handled by sending long streams of data in a parallel-pipelined fashion. The problem is to find a schedule for the POT that minimizes the total response time. This problem has only been previously addressed for homogeneous environments, but the new parallel database systems tend to be more heterogeneous. In this paper, we consider processors with different fixed speeds (called uniform processor system). This problem has been shown to be NP-hard even for identical processors. We propose three approximate algorithms for some special cases of the problem with good low-performance ratio (or approximation factor) bound in the worst case. The performance ratios of these algorithms, even for the general case, are shown by experimentation to be near optimal on the average. We will show that the performance ratios of these algorithms, if used for homogeneous systems, are lower than the previous results. For the general case, we propose an algorithm which has a constant bound on the performance ratio in the worst case and is near optimal on the average.