1 // Copyright (c) 2011 The LevelDB Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file. See the AUTHORS file for names of contributors.
4
5 #include <math.h>
6 #include <stdio.h>
7 #include "port/port.h"
8 #include "util/histogram.h"
9
10 namespace leveldb {
11
12 const double Histogram::kBucketLimit[kNumBuckets] = {
13 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 14, 16, 18, 20, 25, 30, 35, 40, 45,
14 50, 60, 70, 80, 90, 100, 120, 140, 160, 180, 200, 250, 300, 350, 400, 450,
15 500, 600, 700, 800, 900, 1000, 1200, 1400, 1600, 1800, 2000, 2500, 3000,
16 3500, 4000, 4500, 5000, 6000, 7000, 8000, 9000, 10000, 12000, 14000,
17 16000, 18000, 20000, 25000, 30000, 35000, 40000, 45000, 50000, 60000,
18 70000, 80000, 90000, 100000, 120000, 140000, 160000, 180000, 200000,
19 250000, 300000, 350000, 400000, 450000, 500000, 600000, 700000, 800000,
20 900000, 1000000, 1200000, 1400000, 1600000, 1800000, 2000000, 2500000,
21 3000000, 3500000, 4000000, 4500000, 5000000, 6000000, 7000000, 8000000,
22 9000000, 10000000, 12000000, 14000000, 16000000, 18000000, 20000000,
23 25000000, 30000000, 35000000, 40000000, 45000000, 50000000, 60000000,
24 70000000, 80000000, 90000000, 100000000, 120000000, 140000000, 160000000,
25 180000000, 200000000, 250000000, 300000000, 350000000, 400000000,
26 450000000, 500000000, 600000000, 700000000, 800000000, 900000000,
27 1000000000, 1200000000, 1400000000, 1600000000, 1800000000, 2000000000,
28 2500000000.0, 3000000000.0, 3500000000.0, 4000000000.0, 4500000000.0,
29 5000000000.0, 6000000000.0, 7000000000.0, 8000000000.0, 9000000000.0,
30 1e200,
31 };
32
Clear()33 void Histogram::Clear() {
34 min_ = kBucketLimit[kNumBuckets-1];
35 max_ = 0;
36 num_ = 0;
37 sum_ = 0;
38 sum_squares_ = 0;
39 for (int i = 0; i < kNumBuckets; i++) {
40 buckets_[i] = 0;
41 }
42 }
43
Add(double value)44 void Histogram::Add(double value) {
45 // Linear search is fast enough for our usage in db_bench
46 int b = 0;
47 while (b < kNumBuckets - 1 && kBucketLimit[b] <= value) {
48 b++;
49 }
50 buckets_[b] += 1.0;
51 if (min_ > value) min_ = value;
52 if (max_ < value) max_ = value;
53 num_++;
54 sum_ += value;
55 sum_squares_ += (value * value);
56 }
57
Merge(const Histogram & other)58 void Histogram::Merge(const Histogram& other) {
59 if (other.min_ < min_) min_ = other.min_;
60 if (other.max_ > max_) max_ = other.max_;
61 num_ += other.num_;
62 sum_ += other.sum_;
63 sum_squares_ += other.sum_squares_;
64 for (int b = 0; b < kNumBuckets; b++) {
65 buckets_[b] += other.buckets_[b];
66 }
67 }
68
Median() const69 double Histogram::Median() const {
70 return Percentile(50.0);
71 }
72
Percentile(double p) const73 double Histogram::Percentile(double p) const {
74 double threshold = num_ * (p / 100.0);
75 double sum = 0;
76 for (int b = 0; b < kNumBuckets; b++) {
77 sum += buckets_[b];
78 if (sum >= threshold) {
79 // Scale linearly within this bucket
80 double left_point = (b == 0) ? 0 : kBucketLimit[b-1];
81 double right_point = kBucketLimit[b];
82 double left_sum = sum - buckets_[b];
83 double right_sum = sum;
84 double pos = (threshold - left_sum) / (right_sum - left_sum);
85 double r = left_point + (right_point - left_point) * pos;
86 if (r < min_) r = min_;
87 if (r > max_) r = max_;
88 return r;
89 }
90 }
91 return max_;
92 }
93
Average() const94 double Histogram::Average() const {
95 if (num_ == 0.0) return 0;
96 return sum_ / num_;
97 }
98
StandardDeviation() const99 double Histogram::StandardDeviation() const {
100 if (num_ == 0.0) return 0;
101 double variance = (sum_squares_ * num_ - sum_ * sum_) / (num_ * num_);
102 return sqrt(variance);
103 }
104
ToString() const105 std::string Histogram::ToString() const {
106 std::string r;
107 char buf[200];
108 snprintf(buf, sizeof(buf),
109 "Count: %.0f Average: %.4f StdDev: %.2f\n",
110 num_, Average(), StandardDeviation());
111 r.append(buf);
112 snprintf(buf, sizeof(buf),
113 "Min: %.4f Median: %.4f Max: %.4f\n",
114 (num_ == 0.0 ? 0.0 : min_), Median(), max_);
115 r.append(buf);
116 r.append("------------------------------------------------------\n");
117 const double mult = 100.0 / num_;
118 double sum = 0;
119 for (int b = 0; b < kNumBuckets; b++) {
120 if (buckets_[b] <= 0.0) continue;
121 sum += buckets_[b];
122 snprintf(buf, sizeof(buf),
123 "[ %7.0f, %7.0f ) %7.0f %7.3f%% %7.3f%% ",
124 ((b == 0) ? 0.0 : kBucketLimit[b-1]), // left
125 kBucketLimit[b], // right
126 buckets_[b], // count
127 mult * buckets_[b], // percentage
128 mult * sum); // cumulative percentage
129 r.append(buf);
130
131 // Add hash marks based on percentage; 20 marks for 100%.
132 int marks = static_cast<int>(20*(buckets_[b] / num_) + 0.5);
133 r.append(marks, '#');
134 r.push_back('\n');
135 }
136 return r;
137 }
138
139 } // namespace leveldb
140