A method, apparatus and program product that determine a density of a key value referenced in a database query over at least one range of rows, and utilize the determined density to optimize the database query. By doing so, the density of various key values may be determined and compared, and a bit map may be generated over the range of rows of the key value that is denser, resulting in a reduction of resources to build and use the bit map. Moreover, from the bit map over the range of rows to be selected after using the determined density, dense regions may be identified that can be used to optimize block I/O's according to the number of rows to be selected based on the query.