Abstract: Flexible and efficient partitioning of a table is accomplished by hashing the key for an entry, and determining a partition for the entry by generating a sequence of pseudo-random numbers using the hashed key as the seed. As many pseudo-random numbers are generated as there are partitions available. The partition in which the entry belongs corresponds to the largest number in the sequence generated with the hashed key and the pseudo-random number generator. In this way, repartitioning of a partitioned table with a first number of partitions to a second number of partitions can be done with minimal movement and upon repartitioning, the new partition is the same partition that would have been implemented had the identical to the partition that would result if a new partitioning was performed with the second number of partitions.

Abstract: In a system for executing database queries, a directed graph of logically interconnected tasks represents an execution plan for executing a specified database query. A pair of queues are stored in a computer memory for each pair of interconnected tasks in the directed graph. One of the queues in each pair is a down queue for sending requests from a parent task to a child task, and the other is an up queue for sending replies from the child task to the parent task. Each queue is a circular buffer and includes a head pointer that points to a next location in the queue to be read, and a tail pointer that points to a next location in the queue in which data can be written. Each task checks that a queue is not full before writing data into that queue, and checks that the sibling queue is not empty before reading data from the sibling queue.

Abstract: 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.

Abstract: 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.

Abstract: A system and method for optimizing a database query with improved performance enhancements is herein disclosed. The database query consists of one or more logical expressions. Through the repeated application of one or more rules, the logical expressions are transformed into execution plans. The query optimizer partitions the database query into one or more subproblems with each subproblem consisting of one or more logical expressions. A plan is obtained for each subproblem with the plan for the database query including the plans for each subproblem. The query optimizer is cost-based and uses rules including transformation and implementation rules that are used to perform transformations on the logical expressions in a subproblem in order to produce a plan. The rules are classified into context-free and context-sensitive in order to avoid generating duplicate expressions.

Abstract: A system and method for optimizing a database query is herein disclosed. The system consists of a search engine and a database implementor that determines an optimal plan for executing a SQL query. The SQL query is represented as a query tree consisting of a number of nested expressions. The search engine generates a number of plans from which an optimal plan is selected. Plans are generated through the application of a set of rules consisting of implementation and transformation rules. Implementation rules are used to obtain plans. Transformation rules are used to determine equivalent expressions. A plan for the query tree entails finding plans for each expression within the tree where each plan is generated in accordance with a prescribed set of rules. The database implementor selects the set of rules such that more promising plans are generated rather than generating all possible plans.

Abstract: A system and method for optimizing a database query with improved performance enhancements is herein disclosed. The database query consists of one or more logical expressions. Through the repeated application of one or more rules, the logical expressions are transformed into physical expressions and in some cases, execution plans that implement the database query. Each expression has associated with it a set of group attributes that specifies its characteristic inputs and outputs and a cost that estimates the computational expense for executing the expression. The group attributes are used to categorize similar expressions into groups that are stored in a search data structure. They are also used to track duplicate expressions. The cost associated with an expression is used to guide the search process to consider those expressions that will produce low cost plans.

Abstract: A method for subquery elimination for a relational model database based on the SQL language running a database management system (DBMS) under the TANDEM NONSTOP (tm) operating kernel. A series of seven transformation rules are applied to eliminate nested queries in the SQL language. The method and teachings of the present invention generalizes to all types of nested subqueries in SQL, allowing for more efficient computations, allocation and maintenance of system resources.

Abstract: An SQL program executor and an SOL compiler both include options for avoiding recompilations of execution plans whenever the runtime object and the compile time object referenced by an execution plan meet predefined schema similarity criteria. Thus, recompilation is sometimes avoided even though the compile time object has been altered or the run time object is not the same object as the compile time object. To enable late binding, schema information is stored in each execution plan for each object to be accessed by the execution plan. The stored schema information is a subset of the full object schema, and includes information about all the aspects of the objects to be accessed which must remain unchanged in order for the execution plan to be operable. While executing a compiled program, the SQL executor avoids recompilations of execution plans whenever the runtime object and the compile time object referenced by an execution plan meet predefined schema similarity criteria.

Abstract: A database computer system includes memory, residing in a plurality of interconnected computer nodes, for storing database tables. Each database table has a plurality of columns, a primary key index based on a specified subset of the columns, and an associated table schema. At least a subset of the database tables are partitioned into a plurality of partitions, each partition storing records having primary key values in a primary key range distinct from the other partitions. A transaction manager generates and stores an audit trail, each audit entry denoting a database table record event, such as an addition, deletion or alteration of a specified database table record in a specified one of said database tables. Four online data definition procedures allow the structure of a database table to be altered while the database table remains available to execution of transactions, with minimal impact of the availability of the database table for transaction execution.