International Business Machines Corporation

Tam Minh Dai Tran

Nimrod Megiddo

Volker Gerhard Markl

Vincent Corvinelli

John Frederick Hornibrook

Marcel Kutsch

Yuri Deigin

Eileen Tien Lin

Fatma Ozcan

Andrey Balmin

Anjali Betawadkar-Norwood

Techniques are described for optimizing a multi-fact star schema query to retrieve data from two or more fact tables of a database. The optimization techniques may include internally transforming a received multi-fact star schema query into a group of single-fact sub-queries, thereby reducing or eliminating certain constraints during query processing. The group of sub-queries may be enumerated to determine a query execution plan. The multi-fact star schema query may be executed according to the query execution plan to retrieve the data from the two or more fact tables of the database.

Multi-fact query processing in data processing system

A method for consistent selectivity estimation based on the principle of maximum entropy (ME) is provided. The method efficiently exploits all available information and avoids the bias problem. In the absence of detailed knowledge, the ME approach reduces to standard uniformity and independence assumptions. The disclosed method, based on the principle of ME, is used to improve the optimizer's cardinality estimates by orders of magnitude, resulting in better plan quality and significantly reduced query execution times.

Selectivity estimation for conjunctive predicates in the presence of partial knowledge about multivariate data distributions

A system for estimating cardinalities for a plurality of columns in a database system is disclosed. The system include obtaining statistics collected for the plurality of columns. A first portion of the statistics indicates at least one relationship between at least a portion of the plurality of columns, while a second portion of the statistics includes single column statistics. The system also include utilizing the first portion and the second portion of the statistics to estimate the cardinality for the plurality of columns.

System for estimating cardinality in a database system

An apparatus, system, and method are disclosed for optimization of XPath expressions in a database management system configured to accept XML queries. Operations of the method include receiving an XQuery representation and partitioning XPath expressions within the XQuery representation into a plurality of XPath expression clusters. The XPath expression clusters may comprise one or more XPath expressions and those in each cluster may operate on a common document. Furthermore, the XPath expressions in each cluster are hierarchically related to each other such that branch nodes of the cluster are executable independent of nodes in other XPath expression clusters. The method also defines merging the one or more XPath expressions into one or more expression trees for each XPath expression cluster. The method generates one or more query execution plans from the one or more XPath expression blocks. The method includes, for each query execution plan, splitting each of the XPath expression blocks into one or more ordered fragments. The method determines a cardinality according to database statistics and an execution cost for each XPath expression block within each query execution plan. Finally, the method determines an aggregate cardinality for each query execution plan and an aggregate execution cost for each query execution plan. Therefore, an XQuery may be optimized at both the global XQuery and local XPath expression block level, improving performance and reducing overhead.

Optimization of extensible markup language path language (XPATH) expressions in a database management system configured to accept extensible markup language (XML) queries

A method and system for estimating cardinalities for a plurality of columns in a database system is disclosed. The method and system include obtaining statistics collected for the plurality of columns. A first portion of the statistics indicates at least one relationship between at least a portion of the plurality of columns, while a second portion of the statistics includes single column statistics. The method and system also include utilizing the first portion and the second portion of the statistics to estimate the cardinality for the plurality of columns.

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San Jose, CA, United States of America

Tam Minh Dai Tran