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improve-histogram-performance: remove valueIndexMap_ (#8625)

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Summary:
`valueIndexMap_` in histogram is redundant and search in `valueIndexMap_` is slower than search in `bucketValues_`.

this PR delete `valueIndexMap_` and search in `bucketValues_` by `std::lower_bound`

Pull Request resolved: https://github.com/facebook/rocksdb/pull/8625

Reviewed By: zhichao-cao

Differential Revision: D31613386

Pulled By: ajkr

fbshipit-source-id: d7415d724f5c8f41f80cbe82afd7467cfad6f009
This commit is contained in:
leipeng 2021-10-14 14:44:15 -07:00 committed by Facebook GitHub Bot
parent c246c9c6e2
commit 97b30dee5b
2 changed files with 8 additions and 16 deletions
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23
monitoring/histogram.cc
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@ -10,6 +10,8 @@
#include "monitoring/histogram.h"
#include <stdio.h>
#include <algorithm>
#include <cassert>
#include <cinttypes>
#include <cmath>
@ -23,7 +25,6 @@ HistogramBucketMapper::HistogramBucketMapper() {
// If you change this, you also need to change
// size of array buckets_ in HistogramImpl
bucketValues_ = {1, 2};
valueIndexMap_ = {{1, 0}, {2, 1}};
double bucket_val = static_cast<double>(bucketValues_.back());
while ((bucket_val = 1.5 * bucket_val) <= static_cast<double>(port::kMaxUint64)) {
bucketValues_.push_back(static_cast<uint64_t>(bucket_val));
@ -35,26 +36,18 @@ HistogramBucketMapper::HistogramBucketMapper() {
pow_of_ten *= 10;
}
bucketValues_.back() *= pow_of_ten;
valueIndexMap_[bucketValues_.back()] = bucketValues_.size() - 1;
}
maxBucketValue_ = bucketValues_.back();
minBucketValue_ = bucketValues_.front();
}
size_t HistogramBucketMapper::IndexForValue(const uint64_t value) const {
if (value >= maxBucketValue_) {
return bucketValues_.size() - 1;
} else if ( value >= minBucketValue_ ) {
std::map<uint64_t, uint64_t>::const_iterator lowerBound =
valueIndexMap_.lower_bound(value);
if (lowerBound != valueIndexMap_.end()) {
return static_cast<size_t>(lowerBound->second);
} else {
return 0;
}
} else {
return 0;
}
auto beg = bucketValues_.begin();
auto end = bucketValues_.end();
if (value >= maxBucketValue_)
return end - beg - 1; // bucketValues_.size() - 1
else
return std::lower_bound(beg, end, value) - beg;
}
namespace {

1
monitoring/histogram.h
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@ -48,7 +48,6 @@ class HistogramBucketMapper {
std::vector<uint64_t> bucketValues_;
uint64_t maxBucketValue_;
uint64_t minBucketValue_;
std::map<uint64_t, uint64_t> valueIndexMap_;
};
struct HistogramStat {