1. For a database management system to be operatively coupled to a data processing system, the data processing system comprising memory for storing a data table, a method of determining frequency of updating a histogram of the data table, the method comprising: determining sampled histograms for sample portions of the data table over a period of time; computing a difference between at least two of the determined sampled histograms; and determining a frequency with which to update the histogram of the data table depending on the amount of the computed difference.