[jira] [Commented] (KAFKA-5203) Percentilles are calculated incorrectly

["Ivan A. Melnikov (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/KAFKA-5203?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16002583#comment-16002583 ] 

Ivan A. Melnikov commented on KAFKA-5203:
-----------------------------------------

I actually have a fix for this issue. I'll create a pull request shortly.

> Percentilles are calculated incorrectly
> ---------------------------------------
>
>                 Key: KAFKA-5203
>                 URL: https://issues.apache.org/jira/browse/KAFKA-5203
>             Project: Kafka
>          Issue Type: Bug
>          Components: metrics
>            Reporter: Ivan A. Melnikov
>            Priority: Minor
>
> After the samples are purged couple of times, the calculated percentile values tend to decrease comparing to the expected values.
> Consider the following simple example (sorry, idk if I can make it shorter):
> {code}
>         int buckets = 100;
>         Metrics metrics = new Metrics(new MetricConfig().eventWindow(buckets/2).samples(2));
>         Sensor sensor = metrics.sensor("test");
>         sensor.add(new Percentiles(4 * buckets, 100.0, Percentiles.BucketSizing.CONSTANT,
>                 new Percentile(metrics.metricName("test.p50", "grp1"), 50),
>                 new Percentile(metrics.metricName("test.p75", "grp1"), 75)));
>         Metric p50 = metrics.metrics().get(metrics.metricName("test.p50", "grp1"));
>         Metric p75 = metrics.metrics().get(metrics.metricName("test.p75", "grp1"));
>         for (int i = 0; i < buckets; i++) sensor.record(i);
>         System.out.printf("p50=%.3f p75=%.3f\n", p50.value(), p75.value());
>         for (int i = 0; i < buckets; i++) sensor.record(i);
>         System.out.printf("p50=%.3f p75=%.3f\n", p50.value(), p75.value());
>         for (int i = 0; i < buckets; i++) sensor.record(i);
>         System.out.printf("p50=%.3f p75=%.3f\n", p50.value(), p75.value());
> {code}
> The output from this is:
> {noformat}
> p50=50.000 p75=74.490
> p50=24.490 p75=36.735
> p50=15.306 p75=24.490
> {noformat}
> The expected output is, of course, with all three lines similar to the first one.



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