rdingankar commented on code in PR #5486: URL: https://github.com/apache/hadoop/pull/5486#discussion_r1139490394
########## hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/metrics2/util/SampleQuantiles.java: ########## @@ -243,7 +245,12 @@ synchronized public Map<Quantile, Long> snapshot() { Map<Quantile, Long> values = new TreeMap<Quantile, Long>(); for (int i = 0; i < quantiles.length; i++) { - values.put(quantiles[i], query(quantiles[i].quantile)); + /* eg : effectiveQuantile for 0.99 with inverseQuantiles will be 0.01. + For inverse quantiles higher numeric value is better and hence we want + to query from the opposite end of the sorted sample + */ + double effectiveQuantile = inverseQuantiles ? 1 - quantiles[i].quantile : quantiles[i].quantile; + values.put(quantiles[i], query(effectiveQuantile)); Review Comment: Inversing the traversal does not give us the same thing. The iterator is a variable for calculating the allowableError, which becomes high if the traversal is inverted. It will require more math in the allowableError() method based on [CKMS paper.](http://dimacs.rutgers.edu/~graham/pubs/papers/bquant-icde.pdf) Looking for the inverse quantile (1 - quantile) however works as expected as shown in the UT runs from the PR description. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: common-issues-unsubscr...@hadoop.apache.org For queries about this service, please contact Infrastructure at: us...@infra.apache.org --------------------------------------------------------------------- To unsubscribe, e-mail: common-issues-unsubscr...@hadoop.apache.org For additional commands, e-mail: common-issues-h...@hadoop.apache.org