109 lines
2.2 KiB
Go
109 lines
2.2 KiB
Go
package statsd
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import (
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"math"
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"math/rand"
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"sort"
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)
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const defaultPercentileLimit = 1000
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// RunningStats calculates a running mean, variance, standard deviation,
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// lower bound, upper bound, count, and can calculate estimated percentiles.
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// It is based on the incremental algorithm described here:
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// https://en.wikipedia.org/wiki/Algorithms_for_calculating_variance
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type RunningStats struct {
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k float64
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n int64
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ex float64
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ex2 float64
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// Array used to calculate estimated percentiles
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// We will store a maximum of PercLimit values, at which point we will start
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// randomly replacing old values, hence it is an estimated percentile.
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perc []float64
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PercLimit int
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upper float64
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lower float64
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// cache if we have sorted the list so that we never re-sort a sorted list,
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// which can have very bad performance.
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sorted bool
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}
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func (rs *RunningStats) AddValue(v float64) {
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// Whenever a value is added, the list is no longer sorted.
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rs.sorted = false
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if rs.n == 0 {
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rs.k = v
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rs.upper = v
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rs.lower = v
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if rs.PercLimit == 0 {
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rs.PercLimit = defaultPercentileLimit
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}
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rs.perc = make([]float64, 0, rs.PercLimit)
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}
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// These are used for the running mean and variance
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rs.n += 1
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rs.ex += v - rs.k
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rs.ex2 += (v - rs.k) * (v - rs.k)
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// track upper and lower bounds
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if v > rs.upper {
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rs.upper = v
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} else if v < rs.lower {
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rs.lower = v
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}
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if len(rs.perc) < rs.PercLimit {
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rs.perc = append(rs.perc, v)
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} else {
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// Reached limit, choose random index to overwrite in the percentile array
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rs.perc[rand.Intn(len(rs.perc))] = v
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}
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}
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func (rs *RunningStats) Mean() float64 {
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return rs.k + rs.ex/float64(rs.n)
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}
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func (rs *RunningStats) Variance() float64 {
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return (rs.ex2 - (rs.ex*rs.ex)/float64(rs.n)) / float64(rs.n)
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}
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func (rs *RunningStats) Stddev() float64 {
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return math.Sqrt(rs.Variance())
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}
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func (rs *RunningStats) Upper() float64 {
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return rs.upper
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}
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func (rs *RunningStats) Lower() float64 {
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return rs.lower
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}
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func (rs *RunningStats) Count() int64 {
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return rs.n
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}
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func (rs *RunningStats) Percentile(n int) float64 {
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if n > 100 {
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n = 100
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}
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if !rs.sorted {
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sort.Float64s(rs.perc)
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rs.sorted = true
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}
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i := int(float64(len(rs.perc)) * float64(n) / float64(100))
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if i < 0 {
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i = 0
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}
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return rs.perc[i]
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}
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