| 摘要 |
A computer-implemented method, apparatus and article of manufacture for optimizing a database query. A query execution plan for the database query is generated using estimated cost information; one or more steps of the query execution plan are executed to retrieve data from a database stored on the computer system. Actual cost information is generated for each of the executed steps, and the estimated cost information is re-calculated using the actual cost information. One or more resource allocation rules defined on one or more steps of the query execution plan are executed, based on the estimated cost information, wherein the resource allocation rules include one or more defined actions. The estimated cost information may be re-calculated using the actual cost information when confidence in the estimated cost information is low, but the estimated cost information may not be re-calculated when confidence in the estimated cost information is high. In addition, the estimated cost information may be re-calculated using the actual cost information, only when the step has one or more resource allocation rules defined thereon.
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