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Reza Motamedi commented on AURORA1827:

based on the comment description in slaUtils the SlaUtils::percentile reports the percentile
value from the given list ordered in a nondescending 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: AURORA1827
> URL: https://issues.apache.org/jira/browse/AURORA1827
> Project: Aurora
> Issue Type: Story
> Reporter: Reza Motamedi
> Assignee: Reza Motamedi
> Priority: Trivial
> Labels: newbie, sla
>
> The calculation of mttX (mediantimetoX) 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}, 50percentile 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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