Teradata US, Inc.

Dawit Seid

Ahmad Said Ghazal

An execution plan for executing one or more iterations of recursive database queries can be generated in accordance with one aspect of the invention. For example, in accordance with one embodiment of the invention, one or more cardinalities (results or size of results, including intermediate results) associated with one or more iterations can be estimated. This estimation can, for example, by performed by using a sampling or sampling-based algorithm. In addition, a plan generated for execution of one or more iteration of a recursive query can be modified or replaced by comparing the actual cardinality with its estimation. As a result, the first one or more iterations may be executed using a first plan but the subsequent one or more iterations may use a modified or different execution plan.

Cardinality estimation for optimization of recursive or iterative database queries by databases

The number of iterations or self joins required to execute a recursive database query can be estimated. It will be appreciated that this estimation can be used to plan the execution of the recursive query and can be made in various ways and for various applications. By way of example, an estimated number of iterations or self joins required to execute a recursive database query (e.g., 12) can be used as a basis to determine or plan an optimal execution plan. For example, given an estimated twelve (12) iterations, an execution plan can be determined for executing at least the first three (3) iterations or for executing every three (3) iterations, whereas for an estimated twenty (21) iterations required to complete a recursive database query, an execution plan can be determined for the first five (5) or six (6) iterations, and so on.

Estimating number of iterations or self joins required to evaluate iterative or recursive database queries

Based on one or more predicated results (e.g., estimations of the actual results) associated with one or more iterations and/or sub-queries of an iterative or recursive database query, it can be determined whether to use an execution plan (e.g., a current execution plan used to execute one or more iterations) to execute one or more other iterations and/or sub-queries of the iterative or recursive database query. Consequently, use of the execution plan to execute the one or more other iterations and/or sub-queries of the iterative or recursive database query can be disallowed. As a result, the iterative or recursive database query can be executed more efficiently. The determination of whether to use an execution plan can, for example, be performed by determining whether an actual result obtained by executing one or more iterations differs or diverges more than a determined value from an estimated result of the same iteration(s).

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Cary, NC, United States of America

Dawit Seid