610 lines
15 KiB
Go
610 lines
15 KiB
Go
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package metrics
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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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"sync"
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"time"
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)
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const rescaleThreshold = time.Hour
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// Samples maintain a statistically-significant selection of values from
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// a stream.
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type Sample interface {
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Clear()
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Count() int64
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Max() int64
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Mean() float64
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Min() int64
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Percentile(float64) float64
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Percentiles([]float64) []float64
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Size() int
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Snapshot() Sample
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StdDev() float64
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Sum() int64
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Update(int64)
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Values() []int64
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Variance() float64
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}
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// ExpDecaySample is an exponentially-decaying sample using a forward-decaying
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// priority reservoir. See Cormode et al's "Forward Decay: A Practical Time
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// Decay Model for Streaming Systems".
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//
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// <http://www.research.att.com/people/Cormode_Graham/library/publications/CormodeShkapenyukSrivastavaXu09.pdf>
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type ExpDecaySample struct {
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alpha float64
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count int64
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mutex sync.Mutex
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reservoirSize int
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t0, t1 time.Time
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values *expDecaySampleHeap
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}
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// NewExpDecaySample constructs a new exponentially-decaying sample with the
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// given reservoir size and alpha.
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func NewExpDecaySample(reservoirSize int, alpha float64) Sample {
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if UseNilMetrics {
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return NilSample{}
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}
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s := &ExpDecaySample{
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alpha: alpha,
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reservoirSize: reservoirSize,
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t0: time.Now(),
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values: newExpDecaySampleHeap(reservoirSize),
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}
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s.t1 = s.t0.Add(rescaleThreshold)
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return s
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}
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// Clear clears all samples.
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func (s *ExpDecaySample) Clear() {
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s.mutex.Lock()
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defer s.mutex.Unlock()
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s.count = 0
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s.t0 = time.Now()
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s.t1 = s.t0.Add(rescaleThreshold)
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s.values.Clear()
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}
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// Count returns the number of samples recorded, which may exceed the
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// reservoir size.
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func (s *ExpDecaySample) Count() int64 {
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s.mutex.Lock()
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defer s.mutex.Unlock()
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return s.count
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}
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// Max returns the maximum value in the sample, which may not be the maximum
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// value ever to be part of the sample.
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func (s *ExpDecaySample) Max() int64 {
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return SampleMax(s.Values())
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}
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// Mean returns the mean of the values in the sample.
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func (s *ExpDecaySample) Mean() float64 {
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return SampleMean(s.Values())
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}
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// Min returns the minimum value in the sample, which may not be the minimum
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// value ever to be part of the sample.
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func (s *ExpDecaySample) Min() int64 {
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return SampleMin(s.Values())
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}
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// Percentile returns an arbitrary percentile of values in the sample.
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func (s *ExpDecaySample) Percentile(p float64) float64 {
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return SamplePercentile(s.Values(), p)
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}
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// Percentiles returns a slice of arbitrary percentiles of values in the
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// sample.
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func (s *ExpDecaySample) Percentiles(ps []float64) []float64 {
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return SamplePercentiles(s.Values(), ps)
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}
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// Size returns the size of the sample, which is at most the reservoir size.
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func (s *ExpDecaySample) Size() int {
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s.mutex.Lock()
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defer s.mutex.Unlock()
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return s.values.Size()
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}
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// Snapshot returns a read-only copy of the sample.
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func (s *ExpDecaySample) Snapshot() Sample {
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s.mutex.Lock()
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defer s.mutex.Unlock()
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vals := s.values.Values()
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values := make([]int64, len(vals))
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for i, v := range vals {
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values[i] = v.v
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}
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return &SampleSnapshot{
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count: s.count,
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values: values,
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}
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}
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// StdDev returns the standard deviation of the values in the sample.
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func (s *ExpDecaySample) StdDev() float64 {
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return SampleStdDev(s.Values())
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}
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// Sum returns the sum of the values in the sample.
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func (s *ExpDecaySample) Sum() int64 {
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return SampleSum(s.Values())
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}
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// Update samples a new value.
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func (s *ExpDecaySample) Update(v int64) {
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s.update(time.Now(), v)
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}
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// Values returns a copy of the values in the sample.
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func (s *ExpDecaySample) Values() []int64 {
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s.mutex.Lock()
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defer s.mutex.Unlock()
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vals := s.values.Values()
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values := make([]int64, len(vals))
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for i, v := range vals {
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values[i] = v.v
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}
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return values
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}
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// Variance returns the variance of the values in the sample.
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func (s *ExpDecaySample) Variance() float64 {
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return SampleVariance(s.Values())
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}
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// update samples a new value at a particular timestamp. This is a method all
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// its own to facilitate testing.
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func (s *ExpDecaySample) update(t time.Time, v int64) {
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s.mutex.Lock()
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defer s.mutex.Unlock()
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s.count++
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if s.values.Size() == s.reservoirSize {
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s.values.Pop()
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}
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s.values.Push(expDecaySample{
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k: math.Exp(t.Sub(s.t0).Seconds()*s.alpha) / rand.Float64(),
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v: v,
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})
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if t.After(s.t1) {
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values := s.values.Values()
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t0 := s.t0
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s.values.Clear()
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s.t0 = t
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s.t1 = s.t0.Add(rescaleThreshold)
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for _, v := range values {
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v.k = v.k * math.Exp(-s.alpha*s.t0.Sub(t0).Seconds())
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s.values.Push(v)
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}
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}
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}
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// NilSample is a no-op Sample.
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type NilSample struct{}
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// Clear is a no-op.
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func (NilSample) Clear() {}
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// Count is a no-op.
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func (NilSample) Count() int64 { return 0 }
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// Max is a no-op.
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func (NilSample) Max() int64 { return 0 }
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// Mean is a no-op.
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func (NilSample) Mean() float64 { return 0.0 }
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// Min is a no-op.
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func (NilSample) Min() int64 { return 0 }
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// Percentile is a no-op.
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func (NilSample) Percentile(p float64) float64 { return 0.0 }
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// Percentiles is a no-op.
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func (NilSample) Percentiles(ps []float64) []float64 {
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return make([]float64, len(ps))
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}
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// Size is a no-op.
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func (NilSample) Size() int { return 0 }
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// Sample is a no-op.
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func (NilSample) Snapshot() Sample { return NilSample{} }
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// StdDev is a no-op.
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func (NilSample) StdDev() float64 { return 0.0 }
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// Sum is a no-op.
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func (NilSample) Sum() int64 { return 0 }
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// Update is a no-op.
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func (NilSample) Update(v int64) {}
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// Values is a no-op.
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func (NilSample) Values() []int64 { return []int64{} }
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// Variance is a no-op.
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func (NilSample) Variance() float64 { return 0.0 }
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// SampleMax returns the maximum value of the slice of int64.
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func SampleMax(values []int64) int64 {
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if 0 == len(values) {
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return 0
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}
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var max int64 = math.MinInt64
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for _, v := range values {
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if max < v {
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max = v
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}
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}
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return max
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}
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// SampleMean returns the mean value of the slice of int64.
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func SampleMean(values []int64) float64 {
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if 0 == len(values) {
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return 0.0
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}
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return float64(SampleSum(values)) / float64(len(values))
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}
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// SampleMin returns the minimum value of the slice of int64.
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func SampleMin(values []int64) int64 {
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if 0 == len(values) {
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return 0
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}
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var min int64 = math.MaxInt64
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for _, v := range values {
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if min > v {
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min = v
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}
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}
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return min
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}
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// SamplePercentiles returns an arbitrary percentile of the slice of int64.
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func SamplePercentile(values int64Slice, p float64) float64 {
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return SamplePercentiles(values, []float64{p})[0]
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}
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// SamplePercentiles returns a slice of arbitrary percentiles of the slice of
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// int64.
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func SamplePercentiles(values int64Slice, ps []float64) []float64 {
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scores := make([]float64, len(ps))
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size := len(values)
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if size > 0 {
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sort.Sort(values)
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for i, p := range ps {
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pos := p * float64(size+1)
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if pos < 1.0 {
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scores[i] = float64(values[0])
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} else if pos >= float64(size) {
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scores[i] = float64(values[size-1])
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} else {
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lower := float64(values[int(pos)-1])
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upper := float64(values[int(pos)])
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scores[i] = lower + (pos-math.Floor(pos))*(upper-lower)
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}
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}
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}
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return scores
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}
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// SampleSnapshot is a read-only copy of another Sample.
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type SampleSnapshot struct {
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count int64
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values []int64
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}
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// Clear panics.
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func (*SampleSnapshot) Clear() {
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panic("Clear called on a SampleSnapshot")
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}
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// Count returns the count of inputs at the time the snapshot was taken.
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func (s *SampleSnapshot) Count() int64 { return s.count }
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// Max returns the maximal value at the time the snapshot was taken.
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func (s *SampleSnapshot) Max() int64 { return SampleMax(s.values) }
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// Mean returns the mean value at the time the snapshot was taken.
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func (s *SampleSnapshot) Mean() float64 { return SampleMean(s.values) }
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// Min returns the minimal value at the time the snapshot was taken.
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func (s *SampleSnapshot) Min() int64 { return SampleMin(s.values) }
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// Percentile returns an arbitrary percentile of values at the time the
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// snapshot was taken.
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func (s *SampleSnapshot) Percentile(p float64) float64 {
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return SamplePercentile(s.values, p)
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}
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// Percentiles returns a slice of arbitrary percentiles of values at the time
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// the snapshot was taken.
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func (s *SampleSnapshot) Percentiles(ps []float64) []float64 {
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return SamplePercentiles(s.values, ps)
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}
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// Size returns the size of the sample at the time the snapshot was taken.
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func (s *SampleSnapshot) Size() int { return len(s.values) }
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// Snapshot returns the snapshot.
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func (s *SampleSnapshot) Snapshot() Sample { return s }
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// StdDev returns the standard deviation of values at the time the snapshot was
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// taken.
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func (s *SampleSnapshot) StdDev() float64 { return SampleStdDev(s.values) }
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// Sum returns the sum of values at the time the snapshot was taken.
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func (s *SampleSnapshot) Sum() int64 { return SampleSum(s.values) }
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// Update panics.
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func (*SampleSnapshot) Update(int64) {
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panic("Update called on a SampleSnapshot")
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}
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// Values returns a copy of the values in the sample.
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func (s *SampleSnapshot) Values() []int64 {
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values := make([]int64, len(s.values))
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copy(values, s.values)
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return values
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}
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// Variance returns the variance of values at the time the snapshot was taken.
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func (s *SampleSnapshot) Variance() float64 { return SampleVariance(s.values) }
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// SampleStdDev returns the standard deviation of the slice of int64.
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func SampleStdDev(values []int64) float64 {
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return math.Sqrt(SampleVariance(values))
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}
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// SampleSum returns the sum of the slice of int64.
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func SampleSum(values []int64) int64 {
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var sum int64
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for _, v := range values {
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sum += v
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}
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return sum
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}
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// SampleVariance returns the variance of the slice of int64.
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func SampleVariance(values []int64) float64 {
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if 0 == len(values) {
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return 0.0
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}
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m := SampleMean(values)
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var sum float64
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for _, v := range values {
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d := float64(v) - m
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sum += d * d
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}
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return sum / float64(len(values))
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}
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// A uniform sample using Vitter's Algorithm R.
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//
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// <http://www.cs.umd.edu/~samir/498/vitter.pdf>
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type UniformSample struct {
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count int64
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mutex sync.Mutex
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reservoirSize int
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values []int64
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}
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// NewUniformSample constructs a new uniform sample with the given reservoir
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// size.
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func NewUniformSample(reservoirSize int) Sample {
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if UseNilMetrics {
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return NilSample{}
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}
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return &UniformSample{
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reservoirSize: reservoirSize,
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values: make([]int64, 0, reservoirSize),
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}
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}
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// Clear clears all samples.
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func (s *UniformSample) Clear() {
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s.mutex.Lock()
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defer s.mutex.Unlock()
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s.count = 0
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s.values = make([]int64, 0, s.reservoirSize)
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}
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// Count returns the number of samples recorded, which may exceed the
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// reservoir size.
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func (s *UniformSample) Count() int64 {
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s.mutex.Lock()
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defer s.mutex.Unlock()
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return s.count
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}
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// Max returns the maximum value in the sample, which may not be the maximum
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// value ever to be part of the sample.
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func (s *UniformSample) Max() int64 {
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s.mutex.Lock()
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defer s.mutex.Unlock()
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return SampleMax(s.values)
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}
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// Mean returns the mean of the values in the sample.
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func (s *UniformSample) Mean() float64 {
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s.mutex.Lock()
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defer s.mutex.Unlock()
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return SampleMean(s.values)
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}
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// Min returns the minimum value in the sample, which may not be the minimum
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// value ever to be part of the sample.
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func (s *UniformSample) Min() int64 {
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s.mutex.Lock()
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defer s.mutex.Unlock()
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return SampleMin(s.values)
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}
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// Percentile returns an arbitrary percentile of values in the sample.
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func (s *UniformSample) Percentile(p float64) float64 {
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s.mutex.Lock()
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defer s.mutex.Unlock()
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return SamplePercentile(s.values, p)
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}
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// Percentiles returns a slice of arbitrary percentiles of values in the
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// sample.
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func (s *UniformSample) Percentiles(ps []float64) []float64 {
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s.mutex.Lock()
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defer s.mutex.Unlock()
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return SamplePercentiles(s.values, ps)
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}
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// Size returns the size of the sample, which is at most the reservoir size.
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func (s *UniformSample) Size() int {
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s.mutex.Lock()
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defer s.mutex.Unlock()
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return len(s.values)
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}
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// Snapshot returns a read-only copy of the sample.
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func (s *UniformSample) Snapshot() Sample {
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s.mutex.Lock()
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defer s.mutex.Unlock()
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values := make([]int64, len(s.values))
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copy(values, s.values)
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return &SampleSnapshot{
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count: s.count,
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values: values,
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}
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}
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// StdDev returns the standard deviation of the values in the sample.
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func (s *UniformSample) StdDev() float64 {
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s.mutex.Lock()
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defer s.mutex.Unlock()
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return SampleStdDev(s.values)
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}
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// Sum returns the sum of the values in the sample.
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func (s *UniformSample) Sum() int64 {
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s.mutex.Lock()
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defer s.mutex.Unlock()
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return SampleSum(s.values)
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}
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// Update samples a new value.
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func (s *UniformSample) Update(v int64) {
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s.mutex.Lock()
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defer s.mutex.Unlock()
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s.count++
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if len(s.values) < s.reservoirSize {
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s.values = append(s.values, v)
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} else {
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r := rand.Int63n(s.count)
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if r < int64(len(s.values)) {
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s.values[int(r)] = v
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}
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}
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}
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// Values returns a copy of the values in the sample.
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func (s *UniformSample) Values() []int64 {
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s.mutex.Lock()
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defer s.mutex.Unlock()
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values := make([]int64, len(s.values))
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copy(values, s.values)
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return values
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}
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// Variance returns the variance of the values in the sample.
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func (s *UniformSample) Variance() float64 {
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s.mutex.Lock()
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defer s.mutex.Unlock()
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return SampleVariance(s.values)
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}
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// expDecaySample represents an individual sample in a heap.
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type expDecaySample struct {
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k float64
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v int64
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}
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func newExpDecaySampleHeap(reservoirSize int) *expDecaySampleHeap {
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return &expDecaySampleHeap{make([]expDecaySample, 0, reservoirSize)}
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}
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// expDecaySampleHeap is a min-heap of expDecaySamples.
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// The internal implementation is copied from the standard library's container/heap
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type expDecaySampleHeap struct {
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s []expDecaySample
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}
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func (h *expDecaySampleHeap) Clear() {
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h.s = h.s[:0]
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}
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func (h *expDecaySampleHeap) Push(s expDecaySample) {
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n := len(h.s)
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h.s = h.s[0 : n+1]
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h.s[n] = s
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h.up(n)
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}
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func (h *expDecaySampleHeap) Pop() expDecaySample {
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n := len(h.s) - 1
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h.s[0], h.s[n] = h.s[n], h.s[0]
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h.down(0, n)
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n = len(h.s)
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s := h.s[n-1]
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h.s = h.s[0 : n-1]
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return s
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}
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func (h *expDecaySampleHeap) Size() int {
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return len(h.s)
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}
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func (h *expDecaySampleHeap) Values() []expDecaySample {
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return h.s
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}
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func (h *expDecaySampleHeap) up(j int) {
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for {
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i := (j - 1) / 2 // parent
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if i == j || !(h.s[j].k < h.s[i].k) {
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break
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}
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h.s[i], h.s[j] = h.s[j], h.s[i]
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j = i
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}
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}
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func (h *expDecaySampleHeap) down(i, n int) {
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for {
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j1 := 2*i + 1
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if j1 >= n || j1 < 0 { // j1 < 0 after int overflow
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||
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break
|
||
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}
|
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j := j1 // left child
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if j2 := j1 + 1; j2 < n && !(h.s[j1].k < h.s[j2].k) {
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j = j2 // = 2*i + 2 // right child
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}
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if !(h.s[j].k < h.s[i].k) {
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break
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}
|
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h.s[i], h.s[j] = h.s[j], h.s[i]
|
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i = j
|
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}
|
||
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}
|
||
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|
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type int64Slice []int64
|
||
|
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|
||
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func (p int64Slice) Len() int { return len(p) }
|
||
|
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func (p int64Slice) Less(i, j int) bool { return p[i] < p[j] }
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func (p int64Slice) Swap(i, j int) { p[i], p[j] = p[j], p[i] }
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