A data set containing website traffic data or other data is sampled according to a variable sample rate. A target number of samples per time period is established, and a baseline sample rate is determined. Data items in the data set are sampled according to the baseline sample rate, to obtain a sample set. For time periods where the size of the resulting sample set exceeds the target number of samples, a new sample rate is established and the data items for the time period are resampled. Appropriate sampling capability can thus be provided for website traffic in normal time periods, while maintaining capability for handling spikes and other variations in website traffic as may take place in response to certain periodic or non-periodic events.