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From "Reza Motamedi (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (AURORA-1827) Fix SLA percentile calculation
Date Sun, 27 Nov 2016 21:30:58 GMT

    [ https://issues.apache.org/jira/browse/AURORA-1827?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15700339#comment-15700339
] 

Reza Motamedi commented on AURORA-1827:
---------------------------------------

based on the comment description in slaUtils the SlaUtils::percentile reports the percentile
value from the given list ordered in a non-descending order. My concern is with the provided
example. 
   * Example: [30, 60, 70, 90], the 75 percentile is 30 (i.e. 75% of elements are greater).
The current implementation works correctly according to this example. However, if we assume
that assume that these sampled values represent a continuous distribution the 75 percentile
52.5.

I believe the second number captures the underlying distribution better. For instance, having
99 percentile as the input, the current implementation again reports 30, and the second calculation
reports 30.9.


> Fix SLA percentile calculation 
> -------------------------------
>
>                 Key: AURORA-1827
>                 URL: https://issues.apache.org/jira/browse/AURORA-1827
>             Project: Aurora
>          Issue Type: Story
>            Reporter: Reza Motamedi
>            Assignee: Reza Motamedi
>            Priority: Trivial
>              Labels: newbie, sla
>
> The calculation of mttX (median-time-to-X) depends on the computation of percentile values.
The current implementation does not behave nicely with a small sample size. For instance,
for a given sample set of  {50, 150}, 50-percentile is reported to be 50. Although, 100 seems
a more appropriate return value.
> One solution is to modify `SlaUtil` to perform an extrapolation when the sample size
is small or when the corresponding index to a percentile value is not an integer. 



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