Abstract: Disclosed aspects relate to query hint management for a database management system. With respect to a hint for a query, a set of hint profile data is established. The database management system detects a triggering event. Based on the set of hint profile data, the database management system determines to perform a hint action in response to the triggering event. Performance of the hint action is initiated.

Abstract: A database engine and a system running a database engine utilize a dynamic join reordering feature to change the order of two or more join operations while a query is executing. The database engine starts execution of the query with an initial join order setting but monitors the execution of the query to determine whether the initial join order or some other join order would provide better runtime performance. If another join order would provide better performance, then the database engine can change the join order during query execution and complete the query using the new join order.

Abstract: A number of rows that a recursive query will retrieve from a table is estimated by recursively probing an index associated with the table. A recursive query includes a seed and a recursive predicate, each of which is associated with a respective column in the table. If the index has a leading column that matches the table column associated with the seed, and the index has a secondary column that matches the table column associated with the recursive predicate, then the index is recursively probed until a threshold depth of the recursive probing is reached or until all nodes of the index have been examined. The estimated number of rows that the recursive query will retrieve is then calculated based on either the number of rows examined in the index or based on the threshold depth, a cardinality of the secondary column, and a cardinality of the primary column.

Abstract: An apparatus and method to optimize a query access plan in a computer database system. In preferred embodiments, the query optimizer determines the query can be optimized and generates for the query an optimized access plan that eliminates records defined by a Where clause and one or more ordering criteria prior to ordering the records (sorting or grouping) and then returning a first n rows.

Abstract: 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.

Abstract: A database engine and optimizer framework support creation of a series of profiling indices over a column having character string data, such as a traditional “varchar” data type. The profiling indices result in a reduction of the number of records that are searched when searching for a sub-string match within that column. In some embodiments, the series of indices are created over a column that is typically searched using the LIKE predicate or some similar technique; these indices indicate for each record whether certain sub-strings may exist in that record's value in the column. Thus, the indices are used to find the rows that may match one or more portions of the particular term being queried or, in other words, eliminate those records that do not have at least a portion of the term to be matched. The number of records actually retrieved and searched for the query sub-string is thereby reduced.

Abstract: An apparatus, program product and method that employ a dynamic use of Look Ahead Predicate Generation that will enable the database, database engine, and/or query optimizer to alter the processing of a query, and react to sub-optimal access plan selection and additional factors arising after processing has begun, to heal many poor performing queries. Conventional use of LPG requires the query optimizer to decide whether or not to use LPG before the processing of a query begins. As a result, the query optimizer may not only make sub-optimal decisions, but the query optimizer may not consider additional factors that may arise as the query is processing. However, the dynamic use of LPG allows predicates to be built after processing of the query has started and the ability to alter the query's processing to improve query performance.

Abstract: 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.

Abstract: An apparatus and method to optimize a query access plan in a computer database system. In preferred embodiments, the query optimizer determines the query can be optimized and generates for the query an optimized access plan that eliminates records defined by a Where clause and one or more ordering criteria prior to ordering the records (sorting or grouping) and then returning a first n rows.

Abstract: An apparatus and method to optimize a query access plan in a computer database system. In preferred embodiments, the query optimizer determines the query can be optimized and generates for the query an optimized access plan that eliminates records defined by a Where clause and one or more ordering criteria prior to ordering the records (sorting or grouping) and then returning a first n rows.

Abstract: Methods, apparatus, and computer program products are disclosed for debugging a computer program by operating a debugger step function, detecting a governor point by the debugger step function, and, responsive to detecting a governor point, disabling the debugger step function. Debugging a computer program also includes clearing a debugger input buffer of any pending step commands. Debugging a computer program also includes detecting control flow entry into a program control flow structure, recording a return point for each control flow entry into a program control flow structure, and, responsive to a user instruction to do so, continuing program execution to a recorded return point.

Abstract: An apparatus and method highlight entities in a display representation of a database query, result of a database query, and debug message of a database query to indicate associations, statistics, trends, and/or different groupings. Due to conventional techniques used to write database queries, display results of database queries, and the large number of messages in a job log or trace upon executing a database query, these may be confusing. However, highlighting may be applied to the display representations consistent with the invention to indicate associations, statistics, trends, and/or different groupings generally increasing productivity and decreasing human error.

Abstract: An apparatus, program product and method generate 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.

Abstract: Representing a distribution of data by providing a first and a second representation of the distribution of data having defined ranges of data values and a magnitude for each range and creating a third representation of the distribution of data. At least one of the magnitudes for at least one of the ranges of data values in the second representation is more accurate than a magnitude for a corresponding range of data values in the first representation. Creating the third representation of the distribution of data may be carried out by establishing ranges of data values for the third representation in dependence upon ranges from both the first and second representations, and determining a magnitude for each range of data values in the third representation in dependence upon magnitudes for ranges of data values from the first and second representations.

Abstract: A method, apparatus, system, and signal-bearing medium that, in an embodiment, receive a close command directed to a window, and determine whether the close command was received within a close threshold time of the display of the window. If the close command was received within the threshold time, in various embodiments, a close dialog is displayed, the window is faded, the window is shrunk, or a status message is displayed indicating that the window is closing. If a cancel command is received within a cancel-close threshold, the closing of the window is canceled. If the number of times the cancel command has been received for the window exceeds a cancel threshold, then in various embodiments, the close threshold is increased, magnification is recommended, a sound option is recommended, or speech recognition is recommended. In an embodiment, in response to a close command directed to a window, a determination is made whether the number of times the window has been resized is greater than a resize threshold.

Abstract: An apparatus, program product and method that utilize at least one prematurely terminated processing of a database query to improve the processing of the database query. Due to the difficulty of conventional techniques to improve the execution and/or performance of long processing queries, (e.g., advanced user knowledge, assistance from an expert, etc.), users typically terminate long processing queries. As a result, long processing queries may not be improved, and because of the limited options, users may continue to prematurely terminate long processing queries. However, information related to the premature terminations of a database query may be utilized by a DBMS to generate and/or implement suggestions to improve the processing of the database query, resulting in improved query processing, improved performance, fewer premature terminations, and more satisfied users.

Abstract: An apparatus and method to optimize a query access plan in a computer database system. In preferred embodiments, the query optimizer determines the query can be optimized and generates for the query an optimized access plan that eliminates records defined by a Where clause and one or more ordering criteria prior to ordering the records (sorting or grouping) and then returning a first n rows.

Abstract: A method, apparatus, system, and signal-bearing medium that, in an embodiment, estimate a number of rows that a recursive query will retrieve from a table by recursively probing an index associated with the table. A recursive query includes a seed and a recursive predicate, each of which is associated with a respective column in the table. If the index has a leading column that matches the table column associated with the seed, and the index has a secondary column that matches the table column associated with the recursive predicate, then the index is recursively probed until a threshold depth of the recursive probing is reached or until all nodes of the index have been examined.

Abstract: An apparatus, program product and method that employ a dynamic use of Look Ahead Predicate Generation that will enable the database, database engine, and/or query optimizer to alter the processing of a query, and react to sub-optimal access plan selection and additional factors arising after processing has begun, to heal many poor performing queries. Conventional use of LPG requires the query optimizer to decide whether or not to use LPG before the processing of a query begins. As a result, the query optimizer may not only make sub-optimal decisions, but the query optimizer may not consider additional factors that may arise as the query is processing. However, the dynamic use of LPG allows predicates to be built after processing of the query has started and the ability to alter the query's processing to improve query performance.

Abstract: An apparatus, program product and method that build column statistics utilizing at least one skew value. The column statistics built using skew values, instead of column statistics built only through random sampling, may be used to more accurately reflect skew values across join networks, and thus enable a query optimizer to better select an access plan that is optimal under current runtime conditions.