356 lines
9 KiB
Go
356 lines
9 KiB
Go
// Copyright 2015 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package trace
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// This file implements histogramming for RPC statistics collection.
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import (
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"bytes"
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"fmt"
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"html/template"
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"log"
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"math"
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"golang.org/x/net/internal/timeseries"
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)
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const (
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bucketCount = 38
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)
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// histogram keeps counts of values in buckets that are spaced
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// out in powers of 2: 0-1, 2-3, 4-7...
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// histogram implements timeseries.Observable
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type histogram struct {
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sum int64 // running total of measurements
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sumOfSquares float64 // square of running total
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buckets []int64 // bucketed values for histogram
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value int // holds a single value as an optimization
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valueCount int64 // number of values recorded for single value
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}
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// AddMeasurement records a value measurement observation to the histogram.
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func (h *histogram) addMeasurement(value int64) {
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// TODO: assert invariant
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h.sum += value
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h.sumOfSquares += float64(value) * float64(value)
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bucketIndex := getBucket(value)
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if h.valueCount == 0 || (h.valueCount > 0 && h.value == bucketIndex) {
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h.value = bucketIndex
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h.valueCount++
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} else {
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h.allocateBuckets()
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h.buckets[bucketIndex]++
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}
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}
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func (h *histogram) allocateBuckets() {
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if h.buckets == nil {
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h.buckets = make([]int64, bucketCount)
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h.buckets[h.value] = h.valueCount
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h.value = 0
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h.valueCount = -1
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}
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}
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func log2(i int64) int {
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n := 0
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for ; i >= 0x100; i >>= 8 {
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n += 8
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}
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for ; i > 0; i >>= 1 {
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n += 1
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}
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return n
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}
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func getBucket(i int64) (index int) {
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index = log2(i) - 1
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if index < 0 {
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index = 0
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}
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if index >= bucketCount {
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index = bucketCount - 1
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}
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return
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}
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// Total returns the number of recorded observations.
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func (h *histogram) total() (total int64) {
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if h.valueCount >= 0 {
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total = h.valueCount
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}
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for _, val := range h.buckets {
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total += int64(val)
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}
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return
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}
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// Average returns the average value of recorded observations.
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func (h *histogram) average() float64 {
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t := h.total()
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if t == 0 {
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return 0
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}
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return float64(h.sum) / float64(t)
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}
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// Variance returns the variance of recorded observations.
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func (h *histogram) variance() float64 {
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t := float64(h.total())
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if t == 0 {
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return 0
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}
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s := float64(h.sum) / t
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return h.sumOfSquares/t - s*s
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}
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// StandardDeviation returns the standard deviation of recorded observations.
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func (h *histogram) standardDeviation() float64 {
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return math.Sqrt(h.variance())
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}
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// PercentileBoundary estimates the value that the given fraction of recorded
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// observations are less than.
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func (h *histogram) percentileBoundary(percentile float64) int64 {
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total := h.total()
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// Corner cases (make sure result is strictly less than Total())
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if total == 0 {
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return 0
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} else if total == 1 {
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return int64(h.average())
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}
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percentOfTotal := round(float64(total) * percentile)
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var runningTotal int64
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for i := range h.buckets {
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value := h.buckets[i]
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runningTotal += value
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if runningTotal == percentOfTotal {
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// We hit an exact bucket boundary. If the next bucket has data, it is a
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// good estimate of the value. If the bucket is empty, we interpolate the
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// midpoint between the next bucket's boundary and the next non-zero
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// bucket. If the remaining buckets are all empty, then we use the
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// boundary for the next bucket as the estimate.
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j := uint8(i + 1)
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min := bucketBoundary(j)
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if runningTotal < total {
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for h.buckets[j] == 0 {
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j++
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}
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}
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max := bucketBoundary(j)
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return min + round(float64(max-min)/2)
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} else if runningTotal > percentOfTotal {
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// The value is in this bucket. Interpolate the value.
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delta := runningTotal - percentOfTotal
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percentBucket := float64(value-delta) / float64(value)
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bucketMin := bucketBoundary(uint8(i))
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nextBucketMin := bucketBoundary(uint8(i + 1))
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bucketSize := nextBucketMin - bucketMin
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return bucketMin + round(percentBucket*float64(bucketSize))
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}
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}
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return bucketBoundary(bucketCount - 1)
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}
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// Median returns the estimated median of the observed values.
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func (h *histogram) median() int64 {
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return h.percentileBoundary(0.5)
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}
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// Add adds other to h.
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func (h *histogram) Add(other timeseries.Observable) {
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o := other.(*histogram)
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if o.valueCount == 0 {
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// Other histogram is empty
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} else if h.valueCount >= 0 && o.valueCount > 0 && h.value == o.value {
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// Both have a single bucketed value, aggregate them
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h.valueCount += o.valueCount
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} else {
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// Two different values necessitate buckets in this histogram
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h.allocateBuckets()
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if o.valueCount >= 0 {
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h.buckets[o.value] += o.valueCount
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} else {
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for i := range h.buckets {
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h.buckets[i] += o.buckets[i]
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}
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}
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}
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h.sumOfSquares += o.sumOfSquares
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h.sum += o.sum
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}
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// Clear resets the histogram to an empty state, removing all observed values.
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func (h *histogram) Clear() {
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h.buckets = nil
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h.value = 0
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h.valueCount = 0
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h.sum = 0
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h.sumOfSquares = 0
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}
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// CopyFrom copies from other, which must be a *histogram, into h.
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func (h *histogram) CopyFrom(other timeseries.Observable) {
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o := other.(*histogram)
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if o.valueCount == -1 {
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h.allocateBuckets()
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copy(h.buckets, o.buckets)
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}
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h.sum = o.sum
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h.sumOfSquares = o.sumOfSquares
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h.value = o.value
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h.valueCount = o.valueCount
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}
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// Multiply scales the histogram by the specified ratio.
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func (h *histogram) Multiply(ratio float64) {
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if h.valueCount == -1 {
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for i := range h.buckets {
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h.buckets[i] = int64(float64(h.buckets[i]) * ratio)
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}
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} else {
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h.valueCount = int64(float64(h.valueCount) * ratio)
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}
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h.sum = int64(float64(h.sum) * ratio)
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h.sumOfSquares = h.sumOfSquares * ratio
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}
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// New creates a new histogram.
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func (h *histogram) New() timeseries.Observable {
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r := new(histogram)
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r.Clear()
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return r
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}
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func (h *histogram) String() string {
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return fmt.Sprintf("%d, %f, %d, %d, %v",
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h.sum, h.sumOfSquares, h.value, h.valueCount, h.buckets)
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}
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// round returns the closest int64 to the argument
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func round(in float64) int64 {
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return int64(math.Floor(in + 0.5))
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}
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// bucketBoundary returns the first value in the bucket.
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func bucketBoundary(bucket uint8) int64 {
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if bucket == 0 {
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return 0
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}
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return 1 << bucket
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}
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// bucketData holds data about a specific bucket for use in distTmpl.
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type bucketData struct {
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Lower, Upper int64
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N int64
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Pct, CumulativePct float64
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GraphWidth int
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}
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// data holds data about a Distribution for use in distTmpl.
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type data struct {
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Buckets []*bucketData
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Count, Median int64
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Mean, StandardDeviation float64
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}
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// maxHTMLBarWidth is the maximum width of the HTML bar for visualizing buckets.
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const maxHTMLBarWidth = 350.0
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// newData returns data representing h for use in distTmpl.
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func (h *histogram) newData() *data {
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// Force the allocation of buckets to simplify the rendering implementation
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h.allocateBuckets()
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// We scale the bars on the right so that the largest bar is
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// maxHTMLBarWidth pixels in width.
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maxBucket := int64(0)
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for _, n := range h.buckets {
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if n > maxBucket {
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maxBucket = n
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}
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}
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total := h.total()
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barsizeMult := maxHTMLBarWidth / float64(maxBucket)
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var pctMult float64
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if total == 0 {
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pctMult = 1.0
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} else {
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pctMult = 100.0 / float64(total)
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}
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buckets := make([]*bucketData, len(h.buckets))
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runningTotal := int64(0)
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for i, n := range h.buckets {
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if n == 0 {
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continue
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}
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runningTotal += n
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var upperBound int64
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if i < bucketCount-1 {
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upperBound = bucketBoundary(uint8(i + 1))
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} else {
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upperBound = math.MaxInt64
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}
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buckets[i] = &bucketData{
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Lower: bucketBoundary(uint8(i)),
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Upper: upperBound,
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N: n,
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Pct: float64(n) * pctMult,
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CumulativePct: float64(runningTotal) * pctMult,
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GraphWidth: int(float64(n) * barsizeMult),
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}
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}
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return &data{
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Buckets: buckets,
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Count: total,
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Median: h.median(),
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Mean: h.average(),
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StandardDeviation: h.standardDeviation(),
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}
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}
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func (h *histogram) html() template.HTML {
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buf := new(bytes.Buffer)
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if err := distTmpl.Execute(buf, h.newData()); err != nil {
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buf.Reset()
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log.Printf("net/trace: couldn't execute template: %v", err)
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}
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return template.HTML(buf.String())
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}
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// Input: data
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var distTmpl = template.Must(template.New("distTmpl").Parse(`
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<table>
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<tr>
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<td style="padding:0.25em">Count: {{.Count}}</td>
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<td style="padding:0.25em">Mean: {{printf "%.0f" .Mean}}</td>
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<td style="padding:0.25em">StdDev: {{printf "%.0f" .StandardDeviation}}</td>
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<td style="padding:0.25em">Median: {{.Median}}</td>
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</tr>
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</table>
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<hr>
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<table>
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{{range $b := .Buckets}}
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{{if $b}}
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<tr>
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<td style="padding:0 0 0 0.25em">[</td>
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<td style="text-align:right;padding:0 0.25em">{{.Lower}},</td>
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<td style="text-align:right;padding:0 0.25em">{{.Upper}})</td>
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<td style="text-align:right;padding:0 0.25em">{{.N}}</td>
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<td style="text-align:right;padding:0 0.25em">{{printf "%#.3f" .Pct}}%</td>
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<td style="text-align:right;padding:0 0.25em">{{printf "%#.3f" .CumulativePct}}%</td>
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<td><div style="background-color: blue; height: 1em; width: {{.GraphWidth}};"></div></td>
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</tr>
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{{end}}
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{{end}}
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</table>
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`))
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