Synonyms
Definition
In general terms, a physical operator is an implementation of a relational operator. For a relational operator, there are many alternative physical operators that implement it, for instance, sort-merge and hash-join provide alternative algorithms for implementing join. The query execution engine provides generic implementations of all physical operators. Typically, each physical operator supports a uniform iterator interface that hides any internal implementation details and allows operators to be combined together. The iterator interface includes the functions: (i) open() that prepares an operator to produce data, (ii) next() that produces an output tuple, and (iii) close() that performs the final bookkeeping.
Key Points
During query processing, an input query is transformed to a plan to be executed by the query execution engine. An execution plan can be thought of as a dataflow graph where the nodes correspond to the...
Access this chapter
Tax calculation will be finalised at checkout
Purchases are for personal use only
Recommended Reading
Graefe G. Query evaluation techniques for large databases. ACM Comput. Surv., 25(2): 73–170, 1993.
Hellerstein J.M., Stonebraker M., and Hamilton J. Architecture of a database system. Found. Trends Databases, 1(2):141–259, 2007.
Ramakrishnan R. and Gehrke J. Database Management Systems. McGraw-Hill, New York, 2003.
Author information
Authors and Affiliations
Editor information
Editors and Affiliations
Rights and permissions
Copyright information
© 2009 Springer Science+Business Media, LLC
About this entry
Cite this entry
Pitoura, E. (2009). Iterator. In: LIU, L., ÖZSU, M.T. (eds) Encyclopedia of Database Systems. Springer, Boston, MA. https://doi.org/10.1007/978-0-387-39940-9_873
Download citation
DOI: https://doi.org/10.1007/978-0-387-39940-9_873
Publisher Name: Springer, Boston, MA
Print ISBN: 978-0-387-35544-3
Online ISBN: 978-0-387-39940-9
eBook Packages: Computer ScienceReference Module Computer Science and Engineering