How Skewness Can Make Your Execution Times Variable
Skewness is one of those topics that for some reason is often ignored, or misunderstood. Skewness is an important part of data handling for the cost-based optimizer. It makes a difference as to what the optimizer decides to do. It is so important that Oracle created new features such as Adaptive Cursor Sharing just to handle the consequences of skewness. Skewness and the types of skewness are so important that in 12c there are more types of histograms to take account of the different ways in which data can be skewed. So understanding skewness is pretty important.