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The areas of schema analysis include: Frequency of re-analyze It astonishes me how many shops prohibit any un-approved production changes and yet re-analyze schema stats weekly.Evidently, they do not understand that the purpose of schema re-analysis is to change their production SQL execution plans, and they act surprised when performance changes! For example, here we refresh statistics using the "auto" option which works with the table monitoring facility to only re-analyze those Oracle tables that have experienced more than a 10% change in row content: "In 11g, I think there are two other ways to get statistics collected for indexed expressions:1) Collect extended statistics directly on the expression.In some cases, the distribution of values within an index will effect the CBOs decision to use an index versus perform a full-table scan.This happens when a where clause has a disproportional amount of values, making a full-table scan cheaper than index access.As a general rule, histograms are used when a column's values warrant a change to the execution plan.To aid in intelligent histogram generation, Oracle uses the method_opt parameter of dbms_stats.
Let's take a close look at each directive and see how it is used to gather top-quality statistics for the cost-based SQL optimizer.
SThe method_opt parameter for dbms_stats is very useful for refreshing statistics when the table and index data change.
The method_opt parameter is also very useful for determining which columns require histograms.
The dbms_stats utility continues to improve and the exciting new features of automatic sample size and automatic histogram generation greatly simplify the job of the Oracle professional.
Many Oracle professional do not realize the important of having good statistics for the Oracle cost-based SQL optimizer (CBO).