Self-tuning histogram and database modeling

摘要

Building histograms by using feedback information about the execution of query workload rather than by examining the data helps reduce the cost of building and maintaining histograms. A method of maintaining self-tuning histograms updates histograms based on feedback about the execution of a user query. A histogram may be initialized using an assumption of uniform distribution of data or by combining existing histograms. A histogram tuner accesses and estimated result in response to a user query generated by using the histogram. The histogram tuner calculates an estimation error based on the result of the user query and the estimated result. The frequencies of histogram buckets are refined based on the estimation error. The bucket bounds of the histogram are restructured based on the refined frequencies. The method may be performed on-line after a user query or off-line by accessing a workload log. By updating a histogram without accessing the database, the cost of building and maintaining histograms is significantly reduced.