International Business Machines Corporation

Michael Steven Faunce

Brian Robert Muras

Shantan Kethireddy

Ulrich Thiemann

Andrew Peter Passe

Wei Hu

John Francis Edwards

Troy David Armstrong

Michael James McDermott

Abdo Esmail Abdo

Michael W Cain

Yasunobu Suginaka

Thomas Richard Crowley

Karl Allen Nielsen

Bruce Marshall Walk

Robert Edward Galbraith

Robert J Bestgen

Randy Lynn Egan

Michael Joseph Corrigan

Kurt Walter Pinnow

David Ray Kahler

Joseph R Edwards

Timothy John Mullins

Robert Douglas Driesch, Jr

Glen Warren Nelson

Scott Alan Bauman

Curtis Neal Boger

Dennis R Martin

Patrick James Christenson

Russell Paul VanDuine

Michael J Anderson

Michael T Roble

Mark Yadlosky

A method and controller for implementing dynamic banding of a storage device, such as a Self Encrypting Device (SED) in a data storage array, and a design structure on which the subject controller circuit resides are provided. The controller dynamically identifies band boundaries for the storage device at the time a data storage array is created, when one or more devices are added into an existing data storage array, and when a replacement device is rebuilt into an exposed array, or an array with a failed device. A storage device band definition is provided based upon the dynamically identified band boundaries for the storage device.

Implementing dynamic banding of self encrypting drive

Methods, systems, and computer program products are provided for query expression evaluation for query optimization. Embodiments include receiving a query including a plurality of predicates; creating a truth table representing the possible solutions to the query; identifying a plurality of intersections of the truth table, the plurality of intersections including each predicate of the query; assigning a selectivity factor to each predicate; determining in dependence upon the selectivity factors for each predicate a selectivity rating for each of the intersections of the truth table; selecting one or more of the intersections in dependence upon the selectivity rating; and determining in dependence upon the selected intersections a percentage of rows in a database table returned by the query; and providing the percentage of rows in the database table to an access plan generator for query optimization.

Query expression evaluation using sample based projected selectivity

A method generates at least one statistic for a temporary table during optimization of a database query before the temporary table is created. By doing so, optimization can proceed on a database query irrespective of the fact that the temporary table may not be materialized until the database query is ultimately executed.

Generating statistics for temporary tables during query optimization

A method, apparatus and program product are provided for representing a database query expression including a plurality of predicates related to one another by at least one logical relation. A list of operands is generated from the database query expression, where each operand is representative of a predicate. Each operand is mapped into an operand map. A data structure is generated based upon the generated list of operands, where the data structure includes a plurality of nodes. Each node includes an operand identifier that identifies at least one operand based upon the operand map. Each node defines a first logical relation between those predicates in the database query expression that are represented by operands identified by the operand identifier for such node. The nodes are arranged relative to one another in the data structure to define at least a second logical relation among predicates in the database query expression.

Expression tree data structure for representing a database query

A method, apparatus and program product to optimize a database query. In a first system having a first dataspace, a query plan is generated for the database query. Remote statistics collection associated with the database query is initiated on a second system having a second dataspace. The remote statistics collection uses the second dataspace, which includes a current copy of at least a portion of the first dataspace on the first system. Database statistics are collected for the first system by analyzing the second dataspace and then communicating the collected database statistics to the first system for use in optimizing database queries executed by the first system.

Database query optimization utilizing remote statistics collection

A database management system predicts a selectivity for database query conditions requiring a join of records from different tables. The system identifies at least one skewed value in a field specified in the join condition, and constructs, for each skewed value, a set of hypothetical query predicates in which the field specified in the join condition is replaced with a constant equal to the skewed value. The system then predicts the selectivity for the hypothetical predicates, using any appropriate prediction technique. The selectivities of the hypothetical predicates are used to predict a selectivity for the original query.

Method and apparatus for predicting selectivity of database query join conditions using hypothetical query predicates having skewed value constants

Building database statistics for use by a query optimizer is beneficial but may over utilize system resources. Accordingly, the frequency that statistics are rebuilt is controlled in order to minimize the effect of the system. In particular, the staleness of the data and the time since the last statistics collection are used to determine whether or not to re-collect statistics. Even for relatively stale data, statistics are not rebuilt until a predetermined time period has passed.

Time-based rebuilding of autonomic table statistics collections

A method, apparatus and program product is provided for optimizing a database query. A query syntax, system generated predicates, and requisite statistics of the database query are analyzed to determine if a predicate structure is a good candidate for a symbol table only data structure. The predicate structure is analyzed to determine if the predicate structure is already encompassed by an encoded vector index. The symbol table only data structure is generated for at least one column in a database table without generating a corresponding vector data structure from an encoded vector index if the predicate structure is a good candidate and not encompassed by an encoded vector index. The symbol table only data structure is maintained by detecting a change in data associated with the symbol table only data structure and updating the symbol table only data structure to reflect the change in the data.

Maintained symbol table only index

An apparatus, program product and method of processing access requests for a direct access storage device utilize a 'fair elevator' algorithm to schedule access requests from a plurality of requesters desiring access to a direct access storage device (DASD). In particular, a fair elevator algorithm arbitrates requests by taking into account both the requesters with which various requests are associated, as well as the relative positions of the data to be accessed on the DASD. By sorting access requests based upon both requester identity and DASD position, both multitasking performance and DASD throughput are improved in a balanced manner, thus improving overall system performance.

Fair elevator scheduling algorithm for direct access storage device

A database query optimizer determines when no optimal index for a query exists, determines whether a sub-optimal index exists, and if so, uses statistical information for each additional key in the sub-optimal index to rewrite the query in a manner that allows traversing the sub-optimal index. The sub-optimal index is then probed using the rewritten query, and the number of estimated returned rows is then used to optimize the query.

Apparatus and method for using values from a frequent values list to bridge additional keys in a database index

A cardinality estimator computes an estimated cardinality for a database column using a formula that accounts for skew in the data in the column. The result is an estimate of cardinality that more closely resembles the actual cardinality in the column. The improved cardinality estimate may then be used to make better query optimizations.

Apparatus and method for estimating cardinality when data skew is present

A metadata manager is used in a database management system to collect and maintain metadata associated with a database. Multiple optimizer instances are permitted to access the metadata maintained by the metadata manager, often eliminating the need for individual optimizer instances to retrieve and process metadata directly from the database. As such, the overhead associated with operations such as collecting, refining, retrieving and/or maintaining of metadata can be off-loaded from the optimizer instances, often accelerating individual cost estimation calculations by optimizer instances, facilitating reuse of metadata calculations and refinements, and improving metadata consistency between multiple related cost estimates.

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Rochester, MN, United States of America

Michael Steven Faunce