Histograms in 12c

The optimizer needs good statistics to produce good plan, but when there are any types of skew in the data you may need histograms to help the optimizer.

Before 12c histograms could be expensive to create and, if your data patterns were unlucky, could cause as many problems as they solved. Things are much better in 12.

Historically Oracle gave us frequency histograms and height-balanced histograms, so we start this presentation by looking at the different benefits they offer, the costs involved, and the special cases where better strategies are needed. We then move on to looking at the enhancements to histograms that appear in 12c, and show how they do better than the existing mechanism, in time to build, and in accuracy of content.

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