Compaq Computer Corporation, Inc.

Hewlett-packard Development Company, L.P.

Tandem Computers Incorporated

Compaq

Harry Anthony Leslie

Pedro Celis

Christopher M Farrar

Diana L Shak

David W Birdsall

Michael John Skarpelos

Marek J Fridrich

Awny K Al-omari

Hedieh Yaghmai

Rohit N Jain

Jay H Vaishnav

The invention provides methods for optimizing a database management system process of a query. The methods are suitable for execution in a properly configured computer system. In an embodiment of the invention, a plurality of single column statistics are collected for a plurality of columns. This plurality of single column statistics provides an estimate of row counts and unique entry counts for a singe column operator. A preferred single column statistic is selected from the plurality of single column statistics according to a predetermined criteria. The preferred single column statistic is then stored. A selectivity estimate is then determined for predicates in the query using the preferred single column statistic. The selectivity estimate is used in optimizing processing of the query by the database management system.

Method and system for rowcount estimation with multi-column statistics and histograms

A method and apparatus is disclosed for accurately estimating the cost of a database query, including the total computer resources used and estimated elapsed time for the production of a first row and last row of an operator involved in the query and/or the total resources used and elapsed time for returning the overall response to a database query. The method and apparatus accurately accounts for resources used and elapsed time associated with blocking operators, such as sorts and hash joins, which cannot produce a first row until they have completed their operations.

Database query cost model optimizer

The invention provides a mechanism for using statistics, in connection with various database query cost modeling techniques, to more accurately estimate the number of rows and UECs that will be produced by relational operators and predicates in database systems. The ability to accurately estimate the number of rows and UECs returned by a relational operator and/or a predicate is fundamental to computing the cost of a query execution plan. This, in turn, drives the optimizer's ability to select the query plan best suited for the desired performance goal. According to the present invention, histogram statistics are synthesized bottom up from the leaf nodes to the root node of a query tree. Given input statistics in the form of histograms for each operand of a relational operator or predicate, the present inventive method and apparatus merge the input statistics in a way that it simulates the effects of the run time operator on the actual data, so as to produce a predicted row count and UEC for each histogram interval representative of the data that actually will be produced by each such operator or predicate in the query tree. A database query optimizer may use these statistics to select and implement an optimal query plan.

Histogram synthesis modeler for a database query optimizer

The present invention applies one or more pruning heuristics to the expression, the binding, and/or the substitute during a database query optimization process. The heuristics identify certain rules that can be eliminated by either not applying the rules and/or not implementing the rules for a given expression and context (if any) based upon one or more flow rates of the expression. The pruning heuristics can eliminate the application of rules based upon the flow rates of the binding or substitute, for example. Examples include (1) not applying (cutting) a MergeJoin rule for a join expression when an inner table is small enough to be stored in a memory space that is allocated for a HashJoin; (2) not applying implementation rules on the substitute of a left-shift rule for an expression if the resulting input data flow rate from the left child of the join is significantly larger in the substitute than in the binding; (3) not applying the join to TSJ (tuple substitute join) rule if the data flow output of the join expression is significantly larger than the data flow input from the inner child of the join expression; or (4) not applying implementation rules on the substitute join expression of a left shift rule if the number of cross products increases and if the data flow rate from the left child is increases.

System and method for reducing compile time in a top down rule based system using rule heuristics based upon the predicted resulting data flow

A database management system (DBMS) provided with a multi-dimensional improved indexed accessing capability using keyed index searching. Individual search keys are constructed from general expression statements created in the DBMS compiler from search queries supplied to the DBMS. Each key column represents another dimension, and both ranges and IN lists can be specified in the search query and used as the predicate values in multiple columns. Missing predicate values in the search query are interpreted as a specification of the minimum and maximum values for the associated search key column. During compile time, the DBMS compiler produces general expressions to be used by the DBMS executor during run time to create the search keys. The DBMS compiler evaluates search queries by associating predicates with clusters and disjunct numbers assigned to each individual disjunct in the search query expression. The DBMS executor uses the general expression from the compiler and eliminates any conflicts among same column predicates, removes redundancies in predicate values and disjuncts and reduces the number of records to be accessed to the minimum required to complete the search query. The individual search keys are generated in the same order as the index to which the search pertains (i.e., increasing or decreasing order).

Database management system with improved indexed accessing

Growing community of inventors

Los Altos Hills, CA, United States of America

Harry Anthony Leslie