The Effects of Estimating
Optimizer Statistics Abstract: Oracle makes access path decisions based on optimizer statistics stored in the data dictionary. DBAs have the option to estimate these statistics based on samples of table data. But unexpected variation in these statistics can occur when using insufficient sample sizes. Under the right circumstances, this can cause a query's execution plan to change, even when the actual data remains constant. This presentation demonstrates one set of conditions where this phenomenon occurs and explores the underlying reasons for this behavior. |
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How Sampling Error Impacts Execution Plans |