Adaptive Cursor Sharing

I am back in Germany, teaching an 11g Performance Tuning course in Munich. There are several New Features in the 11g version related to Performance Tuning, one of them is Adaptive Cursor Sharing.

It adresses the problem that can occurr in earlier versions if you use bindvariables together with indexes on columns that have skewed values. Typically, you create histograms on skewed columns to notify the optimizer of the skew, so that it can use an index if rare values are asked and make a FTS if values with a low selectivity are used.

Bindvariables used to cross that approach – even Bind Peeking did not always resolve the issue, because the first content of the peeked bindvarible determined all future execution plans.

With 11g, this behaviour has changed. In other words: You can have multiple execution plans now with the same statement that uses bindvariables (with different contents). You may find a very nice explanation of this 11g New Feature from the guys who invented it here.

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