A system that detects a change point in a time series of telemetry signals from a computer system. During operation, the system receives the time series of telemetry signals from the computer system. For each element in the time series, the system (1) inserts the element into a data structure which keeps track of the number of elements in the data structure that have a value greater than and that have a value less than the value of the inserted element; and (2) uses the information stored in the data structure to add a contribution by the inserted element to a trend statistic for the time series. The system then uses the trend statistic to select a hypothesis for the trend in the time series.