1. A computer-based method of maintaining a histogram comprising a plurality of buckets, said method as implemented in a database system comprising the steps of: gathering query feedback records from a query execution engine; adding new buckets corresponding to said gathered feedback records to said histogram according to a principle of maximum entropy, said principle of maximum entropy approximating a true data distribution by a simple distribution that is consistent with valid query feedback records, said simple distribution approximated by limiting the total number of buckets to a predetermined budget by eliminating query feedback records having lowest values of a measure of importance until said predetermined budget is met, and outputting said approximated simple distribution.