Encyclopedia of Database Systems

2009 Edition

Query Optimization

  • Evaggelia Pitoura
Reference work entry
DOI: https://doi.org/10.1007/978-0-387-39940-9_861



A query optimizer translates a query into a sequence of physical operators that can be directly carried out by the query execution engine. The output of the optimizer is called a query execution plan. The execution plan may be thought of as a dataflow datagram that pipes data through a graph of query operators. The goal of query optimization is to derive an efficient execution plan in terms of relevant performance measures, such as memory usage and query response time. To achieve this, the optimizer needs to provide: (i) a space of execution plans (search space), (ii) cost estimation techniques to assign a relevant cost to each plan in the search space, and (iii) an enumeration algorithm to search through the space of plans.

Key Points

The query optimizer takes as input a parsed query and produces as output an efficient execution plan for the query. The task of the optimizer is nontrivial, since given a query (i) there are many logically...

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Recommended Reading

  1. 1.
    Chaudhuri S. 1998, An overview of query optimization in relational systems. In Proc. 17th ACM SIGACT-SIGMOD-SIGART Symp. Principles of Database Systems, pp. 34–43.Google Scholar
  2. 2.
    Ioannidis Y. Query optimization. In Handbook of Computer Science, A.B. Tucker (ed.). CRC Press, 1996.Google Scholar
  3. 3.
    Jarke M. and Koch J. Query optimization in database systems. ACM Comput. Surv., 16(2):111–152, 1984.zbMATHMathSciNetGoogle Scholar

Copyright information

© Springer Science+Business Media, LLC 2009

Authors and Affiliations

  • Evaggelia Pitoura
    • 1
  1. 1.University of IoanninaIoanninaGreece