Performant util/histogram.
Summary: Earlier way to record in histogram=> Linear search BucketLimit array to find the bucket and increment the counter Current way to record in histogram=> Store a HistMap statically which points the buckets of each value in the range [kFirstValue, kLastValue); In the proccess use vectors instead of array's and refactor some code to HistogramHelper class. Test Plan: run db_bench with histogram=1 and see a histogram being printed. Reviewers: dhruba, chip, heyongqiang Reviewed By: chip CC: leveldb Differential Revision: https://reviews.facebook.net/D8265
This commit is contained in:
Abhishek Kona
parent
4dcc0c89f4
commit
009034cf12
4
Makefile
4
Makefile
@ -38,6 +38,7 @@ TESTS = \
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c_test \
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cache_test \
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coding_test \
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histogram_test \
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corruption_test \
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crc32c_test \
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db_test \
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@ -149,6 +150,9 @@ cache_test: util/cache_test.o $(LIBOBJECTS) $(TESTHARNESS)
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coding_test: util/coding_test.o $(LIBOBJECTS) $(TESTHARNESS)
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$(CXX) util/coding_test.o $(LIBOBJECTS) $(TESTHARNESS) $(EXEC_LDFLAGS) -o$@ $(LDFLAGS)
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histogram_test: util/histogram_test.o $(LIBOBJECTS) $(TESTHARNESS)
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$(CXX) util/histogram_test.o $(LIBOBJECTS) $(TESTHARNESS) $(EXEC_LDFLAGS) -o$@ $(LDFLAGS)
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corruption_test: db/corruption_test.o $(LIBOBJECTS) $(TESTHARNESS)
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$(CXX) db/corruption_test.o $(LIBOBJECTS) $(TESTHARNESS) $(EXEC_LDFLAGS) -o$@ $(LDFLAGS)
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@ -2,6 +2,7 @@
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file. See the AUTHORS file for names of contributors.
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#include <cassert>
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#include <math.h>
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#include <stdio.h>
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#include "port/port.h"
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@ -9,7 +10,10 @@
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namespace leveldb {
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const double Histogram::kBucketLimit[kNumBuckets] = {
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HistogramBucketMapper::HistogramBucketMapper() :
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// Add newer bucket index here.
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// Should be alwyas added in sorted order.
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bucketValues_({
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1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 14, 16, 18, 20, 25, 30, 35, 40, 45,
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50, 60, 70, 80, 90, 100, 120, 140, 160, 180, 200, 250, 300, 350, 400, 450,
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500, 600, 700, 800, 900, 1000, 1200, 1400, 1600, 1800, 2000, 2500, 3000,
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@ -24,30 +28,50 @@ const double Histogram::kBucketLimit[kNumBuckets] = {
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70000000, 80000000, 90000000, 100000000, 120000000, 140000000, 160000000,
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180000000, 200000000, 250000000, 300000000, 350000000, 400000000,
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450000000, 500000000, 600000000, 700000000, 800000000, 900000000,
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1000000000, 1200000000, 1400000000, 1600000000, 1800000000, 2000000000,
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2500000000.0, 3000000000.0, 3500000000.0, 4000000000.0, 4500000000.0,
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5000000000.0, 6000000000.0, 7000000000.0, 8000000000.0, 9000000000.0,
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1e200,
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};
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1000000000}),
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maxBucketValue_(bucketValues_.back()),
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minBucketValue_(bucketValues_.front()) {
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for (size_t i =0; i < bucketValues_.size(); ++i) {
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valueIndexMap_[bucketValues_[i]] = i;
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}
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}
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const size_t HistogramBucketMapper::IndexForValue(const uint64_t value) const {
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if (value >= maxBucketValue_) {
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return bucketValues_.size() - 1;
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} else if ( value >= minBucketValue_ ) {
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std::map<uint64_t, uint64_t>::const_iterator lowerBound =
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valueIndexMap_.lower_bound(value);
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if (lowerBound != valueIndexMap_.end()) {
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return lowerBound->second;
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} else {
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return 0;
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}
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} else {
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return 0;
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}
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}
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namespace {
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const HistogramBucketMapper bucketMapper;
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}
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Histogram::Histogram() :
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buckets_(std::vector<uint64_t>(bucketMapper.BucketCount(), 0)) {}
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void Histogram::Clear() {
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min_ = kBucketLimit[kNumBuckets-1];
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min_ = bucketMapper.LastValue();
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max_ = 0;
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num_ = 0;
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sum_ = 0;
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sum_squares_ = 0;
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for (int i = 0; i < kNumBuckets; i++) {
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buckets_[i] = 0;
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}
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buckets_.resize(bucketMapper.BucketCount(), 0);
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}
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void Histogram::Add(double value) {
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// Linear search is fast enough for our usage in db_bench
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int b = 0;
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while (b < kNumBuckets - 1 && kBucketLimit[b] <= value) {
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b++;
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}
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buckets_[b] += 1.0;
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void Histogram::Add(uint64_t value) {
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const size_t index = bucketMapper.IndexForValue(value);
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buckets_[index] += 1;
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if (min_ > value) min_ = value;
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if (max_ < value) max_ = value;
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num_++;
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@ -55,13 +79,17 @@ void Histogram::Add(double value) {
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sum_squares_ += (value * value);
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}
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void Histogram::Add(double value) {
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Add(static_cast<uint64_t>(value));
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}
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void Histogram::Merge(const Histogram& other) {
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if (other.min_ < min_) min_ = other.min_;
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if (other.max_ > max_) max_ = other.max_;
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num_ += other.num_;
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sum_ += other.sum_;
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sum_squares_ += other.sum_squares_;
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for (int b = 0; b < kNumBuckets; b++) {
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for (int b = 0; b < bucketMapper.BucketCount(); b++) {
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buckets_[b] += other.buckets_[b];
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}
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}
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@ -73,15 +101,19 @@ double Histogram::Median() const {
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double Histogram::Percentile(double p) const {
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double threshold = num_ * (p / 100.0);
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double sum = 0;
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for (int b = 0; b < kNumBuckets; b++) {
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for (int b = 0; b < bucketMapper.BucketCount(); b++) {
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sum += buckets_[b];
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if (sum >= threshold) {
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// Scale linearly within this bucket
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double left_point = (b == 0) ? 0 : kBucketLimit[b-1];
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double right_point = kBucketLimit[b];
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double left_point = (b == 0) ? 0 : bucketMapper.BucketLimit(b-1);
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double right_point = bucketMapper.BucketLimit(b);
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double left_sum = sum - buckets_[b];
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double right_sum = sum;
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double pos = (threshold - left_sum) / (right_sum - left_sum);
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double pos = 0;
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double right_left_diff = right_sum - left_sum;
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if (right_left_diff != 0) {
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pos = (threshold - left_sum) / (right_sum - left_sum);
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}
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double r = left_point + (right_point - left_point) * pos;
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if (r < min_) r = min_;
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if (r > max_) r = max_;
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@ -116,13 +148,13 @@ std::string Histogram::ToString() const {
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r.append("------------------------------------------------------\n");
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const double mult = 100.0 / num_;
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double sum = 0;
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for (int b = 0; b < kNumBuckets; b++) {
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for (int b = 0; b < bucketMapper.BucketCount(); b++) {
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if (buckets_[b] <= 0.0) continue;
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sum += buckets_[b];
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snprintf(buf, sizeof(buf),
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"[ %7.0f, %7.0f ) %7.0f %7.3f%% %7.3f%% ",
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((b == 0) ? 0.0 : kBucketLimit[b-1]), // left
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kBucketLimit[b], // right
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"[ %ld, %ld ) %ld %7.3f%% %7.3f%% ",
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((b == 0) ? 0 : bucketMapper.BucketLimit(b-1)), // left
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bucketMapper.BucketLimit(b), // right
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buckets_[b], // count
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mult * buckets_[b], // percentage
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mult * sum); // cumulative percentage
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@ -5,36 +5,70 @@
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#ifndef STORAGE_LEVELDB_UTIL_HISTOGRAM_H_
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#define STORAGE_LEVELDB_UTIL_HISTOGRAM_H_
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#include <cassert>
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#include <string>
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#include <vector>
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#include <map>
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namespace leveldb {
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class HistogramBucketMapper {
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public:
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HistogramBucketMapper();
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// converts a value to the bucket index.
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const size_t IndexForValue(const uint64_t value) const;
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// number of buckets required.
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const size_t BucketCount() const {
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return bucketValues_.size();
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}
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uint64_t LastValue() const {
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return maxBucketValue_;
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}
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uint64_t FirstValue() const {
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return minBucketValue_;
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}
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uint64_t BucketLimit(const uint64_t bucketNumber) const {
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assert(bucketNumber < BucketCount());
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return bucketValues_[bucketNumber];
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}
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private:
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const std::vector<uint64_t> bucketValues_;
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const uint64_t maxBucketValue_;
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const uint64_t minBucketValue_;
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std::map<uint64_t, uint64_t> valueIndexMap_;
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};
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class Histogram {
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public:
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Histogram() { }
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~Histogram() { }
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Histogram();
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void Clear();
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void Add(uint64_t value);
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void Add(double value);
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void Merge(const Histogram& other);
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std::string ToString() const;
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double Median() const;
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double Percentile(double p) const;
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double Average() const;
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double StandardDeviation() const;
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private:
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double min_;
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double max_;
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double num_;
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double sum_;
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double sum_squares_;
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std::vector<uint64_t> buckets_;
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enum { kNumBuckets = 154 };
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static const double kBucketLimit[kNumBuckets];
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double buckets_[kNumBuckets];
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double Median() const;
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double Percentile(double p) const;
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double Average() const;
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double StandardDeviation() const;
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};
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} // namespace leveldb
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57
util/histogram_test.cc
Normal file
57
util/histogram_test.cc
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@ -0,0 +1,57 @@
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#include "util/histogram.h"
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#include "util/testharness.h"
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namespace leveldb {
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class HistogramTest { };
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TEST(HistogramTest, BasicOperation) {
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Histogram histogram;
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for (uint64_t i = 1; i <= 100; i++) {
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histogram.Add(i);
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}
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{
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double median = histogram.Median();
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// ASSERT_LE(median, 50);
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ASSERT_GT(median, 0);
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}
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{
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double percentile100 = histogram.Percentile(100.0);
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ASSERT_LE(percentile100, 100.0);
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ASSERT_GT(percentile100, 0.0);
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double percentile99 = histogram.Percentile(99.0);
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double percentile85 = histogram.Percentile(85.0);
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ASSERT_LE(percentile99, 99.0);
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ASSERT_TRUE(percentile99 >= percentile85);
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}
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ASSERT_EQ(histogram.Average(), 50.5); // avg is acurately caluclated.
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}
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TEST(HistogramTest, EmptyHistogram) {
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Histogram histogram;
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ASSERT_EQ(histogram.Median(), 0.0);
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ASSERT_EQ(histogram.Percentile(85.0), 0.0);
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ASSERT_EQ(histogram.Average(), 0.0);
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}
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TEST(HistogramTest, ClearHistogram) {
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Histogram histogram;
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for (uint64_t i = 1; i <= 100; i++) {
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histogram.Add(i);
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}
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histogram.Clear();
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ASSERT_EQ(histogram.Median(), 0);
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ASSERT_EQ(histogram.Percentile(85.0), 0);
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ASSERT_EQ(histogram.Average(), 0);
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}
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} // namespace leveldb
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int main(int argc, char** argv) {
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return leveldb::test::RunAllTests();
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}
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