Encyclopedia of Database Systems

2018 Edition
| Editors: Ling Liu, M. Tamer Özsu

Execution Skew

  • Nikos Hardavellas
  • Ippokratis Pandis
Reference work entry
DOI: https://doi.org/10.1007/978-1-4614-8265-9_1555

Definition

Execution skew is a phenomenon observed during the parallel evaluation of a database query, in which the concurrent operators exhibit disparate execution times.

Key Points

Execution skew is a phenomenon observed in the parallel evaluation of a database query. It arises when there are imbalances in the execution of the operators running in parallel, resulting in some of the operators running for a longer time than others. The differences in execution times may cause some of the processors to remain idle while others still compute a part of the query. Execution skew can be a consequence of other forms of skew within a query, e.g., data skew, or arise because of temporally unavailable resources that affect the execution speed of a unit of work. The database system can minimize execution skew through the careful allocation of processors to operators and the selection of the appropriate parallel query plan. Execution skew arises in both operator-level parallelism as well as...

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Recommended Reading

  1. 1.
    Märtens H. A classification of skew effects in parallel database systems. In: Proceedings of the 7th International Euro-Par Conference; 2001, p. 291–300.CrossRefGoogle Scholar

Copyright information

© Springer Science+Business Media, LLC, part of Springer Nature 2018

Authors and Affiliations

  1. 1.Carnegie Mellon UniversityPittsburghUSA
  2. 2.Amazon Web ServicesSeattleUSA

Section editors and affiliations

  • Anastasia Ailamaki
    • 1
  1. 1.Informatique et CommunicationsEcole Polytechnique Fédérale de LausanneLausanneSwitzerland