1. A system for processing a stream of data events, comprising: a hybrid histogram that provides a running statistical summary of the stream of data events, wherein the hybrid histogram includes a plurality of percentile ranges, a set of boundary values that separate the percentile ranges, and a count associated with each of the percentile ranges; a histogram processing system for identifying a percentile range from the plurality of percentile ranges into which a new data event value falls, and for incrementing the count associated with the identified percentile range; a boundary recalculation system for periodically recalculating the boundary values such that each percentile range includes a substantially similar number of associated counts; and an analysis system that analyzes the hybrid histogram.