| 摘要 |
An autonomic tool that supervises the collection and maintenance of database statistics for query optimization by transparently deciding what statistics to gather, when and in what detail to gather them. Feedback from data-driven statistics collection is simultaneously combined with feedback from query-driven learning-based statistics collection, to better process both rapidly changing data and data that is queried frequently. The invention monitors table activity and decides if the data in a table has changed sufficiently to require a refresh of invalid statistics. The invention determines if the invalidity is due to correlation between purportedly independent data, outdated statistics, or statistics that have too few frequent values. Tables and column groups are ranked in order of statistical invalidity, and a limited computational budget is prioritized by ranking subsequent gathering of improved statistics. Multiple tables can have their statistics refreshed over time, and the maintenance effort is concentrated on the most important tables.
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