Synonyms
Query compilation
Definition
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 equivalent...
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Recommended Reading
Chaudhuri S. An overview of query optimization in relational systems. In: Proceedings of the 17th ACM SIGACT-SIGMOD-SIGART Symposium on Principles of Database Systems; 1998. p. 34–43.
Ioannidis Y. Query optimization. In: Tucker AB, editors. Handbook of computer science. CRC Press; 1996.
Jarke M, Koch J. Query optimization in database systems. ACM Comput Surv. 1984;16(2):111–52.
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Pitoura, E. (2018). Query Optimization. In: Liu, L., Özsu, M.T. (eds) Encyclopedia of Database Systems. Springer, New York, NY. https://doi.org/10.1007/978-1-4614-8265-9_861
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DOI: https://doi.org/10.1007/978-1-4614-8265-9_861
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