Using the 10053 Event to Understand Index Behavior
- Presention (.pdf) and white paper (.pdf) for Rocky Mountain Oracle Users Group (RMOUG) 2009 Training Days Conference
Abstract:
Using or ignoring an index is one of the most important decisions Oracle's Cost Based Optimizer (CBO) can make. The 10053 event traces how the CBO makes this decision and provides valuable insight into this process. Using the 10053 event, this paper demonstrates how changes to critical initialization parameters affect whether index operations get included in execution plans
Using or ignoring an index is one of the most important decisions Oracle's Cost Based Optimizer (CBO) can make. The 10053 event traces how the CBO makes this decision and provides valuable insight into this process. Using the 10053 event, this paper demonstrates how changes to critical initialization parameters affect whether index operations get included in execution plans
How Sampling Error Impacts Execution Plans: The Effects of Estimating Optimizer Statistics
- Published in SELECT, the journal of the Independent Oracle Users Group (IOUG), Q3 2008
- Also presented at Rocky Mountain Oracle Users Group (RMOUG) 2008 Training Days Conference
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.