Add user stats Reset API

Summary:
It resets all the ticker and histogram stats to zero. Needed to change the locking a bit since Reset() is the only operation that manipulates multiple tickers/histograms together, and that operation should be seen as atomic by other operations that access tickers/histograms.
Closes https://github.com/facebook/rocksdb/pull/2213

Differential Revision: D4952232

Pulled By: ajkr

fbshipit-source-id: c0475c3e4c7b940120d53891b69c3091149a0679

db/db_statistics_test.cc

@@ -115,6 +115,31 @@ TEST_F(DBStatisticsTest, MutexWaitStats) {
   ThreadStatusUtil::TEST_SetStateDelay(ThreadStatus::STATE_MUTEX_WAIT, 0);
 }
 
+TEST_F(DBStatisticsTest, ResetStats) {
+  Options options = CurrentOptions();
+  options.create_if_missing = true;
+  options.statistics = rocksdb::CreateDBStatistics();
+  DestroyAndReopen(options);
+  for (int i = 0; i < 2; ++i) {
+    // pick arbitrary ticker and histogram. On first iteration they're zero
+    // because db is unused. On second iteration they're zero due to Reset().
+    ASSERT_EQ(0, TestGetTickerCount(options, NUMBER_KEYS_WRITTEN));
+    HistogramData histogram_data;
+    options.statistics->histogramData(DB_WRITE, &histogram_data);
+    ASSERT_EQ(0.0, histogram_data.max);
+
+    if (i == 0) {
+      // The Put() makes some of the ticker/histogram stats nonzero until we
+      // Reset().
+      ASSERT_OK(Put("hello", "rocksdb"));
+      ASSERT_EQ(1, TestGetTickerCount(options, NUMBER_KEYS_WRITTEN));
+      options.statistics->histogramData(DB_WRITE, &histogram_data);
+      ASSERT_GT(histogram_data.max, 0.0);
+      options.statistics->Reset();
+    }
+  }
+}
+
 }  // namespace rocksdb
 
 int main(int argc, char** argv) {

include/rocksdb/statistics.h

@@ -13,6 +13,8 @@
 #include <memory>
 #include <vector>
 
+#include "rocksdb/status.h"
+
 namespace rocksdb {
 
 /**
@@ -443,6 +445,11 @@ class Statistics {
   virtual uint64_t getAndResetTickerCount(uint32_t tickerType) = 0;
   virtual void measureTime(uint32_t histogramType, uint64_t time) = 0;
 
+  // Resets all ticker and histogram stats
+  virtual Status Reset() {
+    return Status::NotSupported("Not implemented");
+  }
+
   // String representation of the statistic object.
   virtual std::string ToString() const {
     // Do nothing by default

monitoring/statistics.cc

@@ -33,6 +33,10 @@ StatisticsImpl::~StatisticsImpl() {}
 
 uint64_t StatisticsImpl::getTickerCount(uint32_t tickerType) const {
   MutexLock lock(&aggregate_lock_);
+  return getTickerCountLocked(tickerType);
+}
+
+uint64_t StatisticsImpl::getTickerCountLocked(uint32_t tickerType) const {
   assert(
     enable_internal_stats_ ?
       tickerType < INTERNAL_TICKER_ENUM_MAX :
@@ -68,6 +72,12 @@ StatisticsImpl::HistogramInfo::getMergedHistogram() const {
 
 void StatisticsImpl::histogramData(uint32_t histogramType,
                                    HistogramData* const data) const {
+  MutexLock lock(&aggregate_lock_);
+  histogramDataLocked(histogramType, data);
+}
+
+void StatisticsImpl::histogramDataLocked(uint32_t histogramType,
+                                         HistogramData* const data) const {
   assert(
     enable_internal_stats_ ?
       histogramType < INTERNAL_HISTOGRAM_ENUM_MAX :
@@ -76,6 +86,7 @@ void StatisticsImpl::histogramData(uint32_t histogramType,
 }
 
 std::string StatisticsImpl::getHistogramString(uint32_t histogramType) const {
+  MutexLock lock(&aggregate_lock_);
   assert(enable_internal_stats_ ? histogramType < INTERNAL_HISTOGRAM_ENUM_MAX
                                 : histogramType < HISTOGRAM_ENUM_MAX);
   return histograms_[histogramType].getMergedHistogram()->ToString();
@@ -108,6 +119,14 @@ StatisticsImpl::ThreadHistogramInfo* StatisticsImpl::getThreadHistogramInfo(
 void StatisticsImpl::setTickerCount(uint32_t tickerType, uint64_t count) {
   {
     MutexLock lock(&aggregate_lock_);
+    setTickerCountLocked(tickerType, count);
+  }
+  if (stats_ && tickerType < TICKER_ENUM_MAX) {
+    stats_->setTickerCount(tickerType, count);
+  }
+}
+
+void StatisticsImpl::setTickerCountLocked(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_) {
@@ -119,10 +138,6 @@ void StatisticsImpl::setTickerCount(uint32_t tickerType, uint64_t count) {
         nullptr /* res */);
     tickers_[tickerType].merged_sum.store(count, std::memory_order_relaxed);
   }
-  }
-  if (stats_ && tickerType < TICKER_ENUM_MAX) {
-    stats_->setTickerCount(tickerType, count);
-  }
 }
 
 uint64_t StatisticsImpl::getAndResetTickerCount(uint32_t tickerType) {
@@ -176,6 +191,21 @@ void StatisticsImpl::measureTime(uint32_t histogramType, uint64_t value) {
   }
 }
 
+Status StatisticsImpl::Reset() {
+  MutexLock lock(&aggregate_lock_);
+  for (uint32_t i = 0; i < TICKER_ENUM_MAX; ++i) {
+    setTickerCountLocked(i, 0);
+  }
+  for (uint32_t i = 0; i < HISTOGRAM_ENUM_MAX; ++i) {
+    histograms_[i].thread_value->Fold(
+        [](void* curr_ptr, void* res) {
+          static_cast<HistogramImpl*>(curr_ptr)->Clear();
+        },
+        nullptr /* res */);
+  }
+  return Status::OK();
+}
+
 namespace {
 
 // a buffer size used for temp string buffers
@@ -184,13 +214,14 @@ const int kTmpStrBufferSize = 200;
 } // namespace
 
 std::string StatisticsImpl::ToString() const {
+  MutexLock lock(&aggregate_lock_);
   std::string res;
   res.reserve(20000);
   for (const auto& t : TickersNameMap) {
     if (t.first < TICKER_ENUM_MAX || enable_internal_stats_) {
       char buffer[kTmpStrBufferSize];
       snprintf(buffer, kTmpStrBufferSize, "%s COUNT : %" PRIu64 "\n",
-               t.second.c_str(), getTickerCount(t.first));
+               t.second.c_str(), getTickerCountLocked(t.first));
       res.append(buffer);
     }
   }
@@ -198,7 +229,7 @@ std::string StatisticsImpl::ToString() const {
     if (h.first < HISTOGRAM_ENUM_MAX || enable_internal_stats_) {
       char buffer[kTmpStrBufferSize];
       HistogramData hData;
-      histogramData(h.first, &hData);
+      histogramDataLocked(h.first, &hData);
       snprintf(
           buffer, kTmpStrBufferSize,
           "%s statistics Percentiles :=> 50 : %f 95 : %f 99 : %f 100 : %f\n",

monitoring/statistics.h

@@ -45,6 +45,7 @@ class StatisticsImpl : public Statistics {
   virtual void recordTick(uint32_t ticker_type, uint64_t count) override;
   virtual void measureTime(uint32_t histogram_type, uint64_t value) override;
 
+  virtual Status Reset() override;
   virtual std::string ToString() const override;
   virtual bool HistEnabledForType(uint32_t type) const override;
 
@@ -52,8 +53,8 @@ class StatisticsImpl : public Statistics {
   std::shared_ptr<Statistics> stats_shared_;
   Statistics* stats_;
   bool enable_internal_stats_;
-  // Synchronizes setTickerCount()/getTickerCount() operations so partially
+  // Synchronizes anything that operates on other threads' thread-specific data
-  // completed setTickerCount() won't be visible.
+  // such that operations like Reset() can be performed atomically.
   mutable port::Mutex aggregate_lock_;
 
   // Holds data maintained by each thread for implementing tickers.
@@ -126,6 +127,11 @@ class StatisticsImpl : public Statistics {
     std::unique_ptr<HistogramImpl> getMergedHistogram() const;
   };
 
+  uint64_t getTickerCountLocked(uint32_t ticker_type) const;
+  void histogramDataLocked(uint32_t histogram_type,
+                           HistogramData* const data) const;
+  void setTickerCountLocked(uint32_t ticker_type, uint64_t count);
+
   // Returns the info for this tickerType/thread. It sets a new info with zeroed
   // counter if none exists.
   ThreadTickerInfo* getThreadTickerInfo(uint32_t ticker_type);