Estimation and use of access plan statistics
AssigneeInternational Business Machines Corporation
InventorsAbdo Esmail Abdo, Larry Wayne Loen
Life of this patent
Estimating the term…
Abstract
In processing a query including a selection criterion on one or more attributes of a relation, a prior statistic generated for a prior different selection criterion on the same one or more attributes of the relation, may be revalidated for use in processing the query, based upon a measure of the entropy of the one or more attributes of the relation. In this way, the re-validation of statistics may be performed more efficiently. Furthermore, attribute groups of a relation for which multi-dimensional indexes are to be formed, are identified by evaluating the correlation of attribute values within tuples of the relation and determining that the correlation of attribute values within tuples of the relation exceeds a threshold.
Claims24
A method for revalidating previously generated statistics for a query directed to one or more attributes of a relation, comprising
- identifying in said query a selection criterion on said one or more attributes of said relation, and
- revalidating a prior statistic generated for a prior different selection criterion on the same one or more attributes of said relation, based upon a measure of entropy of said one or more attributes of said relation.
A computer system implementing a relational database system and evaluating queries directed to said relational database, comprising
- storage for said relational database, including a relation having a plurality of tuples including values for a plurality of attributes, and
- computing circuitry performing query optimization and query execution upon said relational database, said query optimization including generating statistics for a query directed to one or more attributes of said relation, by identifying in said query a selection criterion on said one or more attributes of said relation, by revalidating a prior statistic generated for a prior different selection criterion on the same one or more attributes of said relation, based upon a measure of entropy of said one or more attributes of said relation.
A program product for implementing a relational database system and evaluating queries directed to said relational database, comprising
- a relational database, including a relation having a plurality of tuples including values for a plurality of attributes, and
- relational database software performing query optimization and query execution upon said relational database, said query optimization including generating statistics for a query directed to one or more attributes of said relation, by identifying in said query a selection criterion on said one or more attributes of said relation, by revalidating a prior statistic generated for a prior different selection criterion on the same one or more attributes of said relation, based upon a measure of entropy of said one or more attributes of said relation, and
- a signal bearing media holding said relational database and relational database software.
A method for identifying a group of attributes of a relation for which a multi-dimensional index is to be formed, comprising
- computing a correlation of attribute values within tuples of the relation, and
- forming a multi-dimensional index for a group of attributes within tuples of the relation having a correlation of attribute values in excess of a threshold.
A computer system implementing a relational database system including indexes for said relational database, comprising
- storage for said relational database, including a relation having a plurality of tuples including values for a plurality of attributes, and
- computing circuitry performing query execution upon said relational database, and identifying a group of attributes of a relation for which a multi-dimensional index is to be formed, by computing a correlation of attribute values within tuples of the relation, and forming a multi-dimensional index for a group of attributes within tuples of the relation having a correlation of attribute values in excess of a threshold.
A program product for implementing a relational database system, comprising
- a relational database, including a relation having a plurality of tuples including values for a plurality of attributes,
- relational database software performing query execution upon said relational database, and identifying a group of attributes of a relation for which a multi-dimensional index is to be formed, by computing a correlation of attribute values within tuples of the relation, and forming a multi-dimensional index for a group of attributes within tuples of the relation having a correlation of attribute values in excess of a threshold, and
- a signal bearing media holding said relational database and relational database software.
Dependencies are inferred from the claim text.