010644: Some statistics are approximate.


When there are more than a million unique values in a zone, the Majority, Median, Minority, Percentile, and Variety statistic values may be approximate.

The statistics are computed using the Greenwald Khanna algorithm (Greenwald, M., & Khanna, S., 2001). For Median and Percentile, the true percentile value of the result is within 0.0001 percent of the requested percentile value. For example, with Median, the true percentile value of the result is somewhere between the 49.9999 percentile and the 50.0001 percentile. The Majority, Minority, and Variety statistics are also estimated from the Greenwall-Khanna data structure but do not have well defined bounds on their errors.

Reference: Greenwald, M., & Khanna, S. (2001). "Space-efficient online computation of quantile summaries" ACM SIGMOD Record, 30(2), 58-66.


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