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