| 摘要 |
A database query optimizer allows specifying a performance specification for a query. When an access plan is created, the actual performance for executing the query using the access plan is determined and compared to the performance specification for the query. If the actual performance does not satisfy the performance specification for the query, the query optimizer autonomically generates a different access plan to see if the performance improves. If an access plan that meets the performance specification is generated, the new access plan is stored in the access plan cache for the query. If no access plan can be generated that meets the performance specification for the query, the access plan that provided the best performance is selected and stored in the access plan cache for the query.
|
