rocksdb/util/statistics.cc
Andrew Kryczka 1613fa9490 Thread-specific histogram statistics
Summary:
To reduce contention for atomics when HistogramStats are shared across
threads, this diff makes them thread-specific so updates are faster. This comes
at the expense of slower reads (much less frequent), which now require merging
all histograms. In this diff,

- Thread-specific HistogramImpl is created upon the thread's first measureTime()
- Thread-specific HistogramImpl are merged and deleted upon thread termination or ThreadLocalPtr destruction, whichever comes first
- getHistogramString() and histogramData() merge all histograms, both thread-specific and previously merged ones

Test Plan:
unit tests, ran db_bench and verified histograms look similar

before:

  $ TEST_TMPDIR=/dev/shm/ perf record -g ./db_bench --benchmarks=readwhilewriting --statistics --num=1000000 --use_existing_db --threads=64 --cache_size=250000000 --compression_type=lz4
  ...
  +    7.63%  db_bench     db_bench             [.] rocksdb::HistogramStat::Add

after:

  $ TEST_TMPDIR=/dev/shm/ perf record -g ./db_bench --benchmarks=readwhilewriting --statistics --num=1000000 --use_existing_db --threads=64 --cache_size=250000000 --compression_type=lz4
  ...
  +    0.98%  db_bench     db_bench             [.] rocksdb::HistogramStat::Add

Reviewers: sdong, MarkCallaghan, kradhakrishnan, IslamAbdelRahman

Reviewed By: IslamAbdelRahman

Subscribers: andrewkr, dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D62649
2016-08-31 14:02:09 -07:00

199 lines
6.3 KiB
C++

// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
// This source code is licensed under the BSD-style license found in the
// LICENSE file in the root directory of this source tree. An additional grant
// of patent rights can be found in the PATENTS file in the same directory.
//
#include "util/statistics.h"
#ifndef __STDC_FORMAT_MACROS
#define __STDC_FORMAT_MACROS
#endif
#include <inttypes.h>
#include "rocksdb/statistics.h"
#include "port/likely.h"
#include <algorithm>
#include <cstdio>
namespace rocksdb {
std::shared_ptr<Statistics> CreateDBStatistics() {
return std::make_shared<StatisticsImpl>(nullptr, false);
}
StatisticsImpl::StatisticsImpl(
std::shared_ptr<Statistics> stats,
bool enable_internal_stats)
: stats_shared_(stats),
stats_(stats.get()),
enable_internal_stats_(enable_internal_stats) {
}
StatisticsImpl::~StatisticsImpl() {}
uint64_t StatisticsImpl::getTickerCount(uint32_t tickerType) const {
MutexLock lock(&aggregate_lock_);
assert(
enable_internal_stats_ ?
tickerType < INTERNAL_TICKER_ENUM_MAX :
tickerType < TICKER_ENUM_MAX);
uint64_t thread_local_sum = 0;
tickers_[tickerType].thread_value->Fold(
[](void* curr_ptr, void* res) {
auto* sum_ptr = static_cast<uint64_t*>(res);
*sum_ptr += static_cast<std::atomic_uint_fast64_t*>(curr_ptr)->load(
std::memory_order_relaxed);
},
&thread_local_sum);
return thread_local_sum +
tickers_[tickerType].merged_sum.load(std::memory_order_relaxed);
}
std::unique_ptr<HistogramImpl>
StatisticsImpl::HistogramInfo::getMergedHistogram() const {
MutexLock lock(&merge_lock);
std::unique_ptr<HistogramImpl> res_hist(new HistogramImpl());
res_hist->Merge(merged_hist);
thread_value->Fold(
[](void* curr_ptr, void* res) {
auto tmp_res_hist = static_cast<HistogramImpl*>(res);
auto curr_hist = static_cast<HistogramImpl*>(curr_ptr);
tmp_res_hist->Merge(*curr_hist);
},
res_hist.get());
return res_hist;
}
void StatisticsImpl::histogramData(uint32_t histogramType,
HistogramData* const data) const {
assert(
enable_internal_stats_ ?
histogramType < INTERNAL_HISTOGRAM_ENUM_MAX :
histogramType < HISTOGRAM_ENUM_MAX);
histograms_[histogramType].getMergedHistogram()->Data(data);
}
std::string StatisticsImpl::getHistogramString(uint32_t histogramType) const {
assert(enable_internal_stats_ ? histogramType < INTERNAL_HISTOGRAM_ENUM_MAX
: histogramType < HISTOGRAM_ENUM_MAX);
return histograms_[histogramType].getMergedHistogram()->ToString();
}
StatisticsImpl::ThreadTickerInfo* StatisticsImpl::getThreadTickerInfo(
uint32_t tickerType) {
auto info_ptr =
static_cast<ThreadTickerInfo*>(tickers_[tickerType].thread_value->Get());
if (info_ptr == nullptr) {
info_ptr =
new ThreadTickerInfo(0 /* value */, &tickers_[tickerType].merged_sum);
tickers_[tickerType].thread_value->Reset(info_ptr);
}
return info_ptr;
}
StatisticsImpl::ThreadHistogramInfo* StatisticsImpl::getThreadHistogramInfo(
uint32_t histogram_type) {
auto info_ptr = static_cast<ThreadHistogramInfo*>(
histograms_[histogram_type].thread_value->Get());
if (info_ptr == nullptr) {
info_ptr = new ThreadHistogramInfo(&histograms_[histogram_type].merged_hist,
&histograms_[histogram_type].merge_lock);
histograms_[histogram_type].thread_value->Reset(info_ptr);
}
return info_ptr;
}
void StatisticsImpl::setTickerCount(uint32_t tickerType, uint64_t count) {
{
MutexLock lock(&aggregate_lock_);
assert(enable_internal_stats_ ? tickerType < INTERNAL_TICKER_ENUM_MAX
: tickerType < TICKER_ENUM_MAX);
if (tickerType < TICKER_ENUM_MAX || enable_internal_stats_) {
tickers_[tickerType].thread_value->Fold(
[](void* curr_ptr, void* res) {
static_cast<std::atomic<uint64_t>*>(curr_ptr)->store(
0, std::memory_order_relaxed);
},
nullptr /* res */);
tickers_[tickerType].merged_sum.store(count, std::memory_order_relaxed);
}
}
if (stats_ && tickerType < TICKER_ENUM_MAX) {
stats_->setTickerCount(tickerType, count);
}
}
void StatisticsImpl::recordTick(uint32_t tickerType, uint64_t count) {
assert(
enable_internal_stats_ ?
tickerType < INTERNAL_TICKER_ENUM_MAX :
tickerType < TICKER_ENUM_MAX);
if (tickerType < TICKER_ENUM_MAX || enable_internal_stats_) {
auto info_ptr = getThreadTickerInfo(tickerType);
info_ptr->value.fetch_add(count, std::memory_order_relaxed);
}
if (stats_ && tickerType < TICKER_ENUM_MAX) {
stats_->recordTick(tickerType, count);
}
}
void StatisticsImpl::measureTime(uint32_t histogramType, uint64_t value) {
assert(
enable_internal_stats_ ?
histogramType < INTERNAL_HISTOGRAM_ENUM_MAX :
histogramType < HISTOGRAM_ENUM_MAX);
if (histogramType < HISTOGRAM_ENUM_MAX || enable_internal_stats_) {
getThreadHistogramInfo(histogramType)->value.Add(value);
}
if (stats_ && histogramType < HISTOGRAM_ENUM_MAX) {
stats_->measureTime(histogramType, value);
}
}
namespace {
// a buffer size used for temp string buffers
const int kBufferSize = 200;
} // namespace
std::string StatisticsImpl::ToString() const {
std::string res;
res.reserve(20000);
for (const auto& t : TickersNameMap) {
if (t.first < TICKER_ENUM_MAX || enable_internal_stats_) {
char buffer[kBufferSize];
snprintf(buffer, kBufferSize, "%s COUNT : %" PRIu64 "\n",
t.second.c_str(), getTickerCount(t.first));
res.append(buffer);
}
}
for (const auto& h : HistogramsNameMap) {
if (h.first < HISTOGRAM_ENUM_MAX || enable_internal_stats_) {
char buffer[kBufferSize];
HistogramData hData;
histogramData(h.first, &hData);
snprintf(
buffer,
kBufferSize,
"%s statistics Percentiles :=> 50 : %f 95 : %f 99 : %f\n",
h.second.c_str(),
hData.median,
hData.percentile95,
hData.percentile99);
res.append(buffer);
}
}
res.shrink_to_fit();
return res;
}
bool StatisticsImpl::HistEnabledForType(uint32_t type) const {
if (LIKELY(!enable_internal_stats_)) {
return type < HISTOGRAM_ENUM_MAX;
}
return true;
}
} // namespace rocksdb