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diff --git a/src/rocksdb/monitoring/histogram_windowing.h b/src/rocksdb/monitoring/histogram_windowing.h
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+++ b/src/rocksdb/monitoring/histogram_windowing.h
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+//  Copyright (c) 2013, Facebook, Inc.  All rights reserved.
+//  This source code is licensed under both the GPLv2 (found in the
+//  COPYING file in the root directory) and Apache 2.0 License
+//  (found in the LICENSE.Apache file in the root directory).
+//
+// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file. See the AUTHORS file for names of contributors.
+
+#pragma once
+
+#include "monitoring/histogram.h"
+
+namespace ROCKSDB_NAMESPACE {
+class SystemClock;
+
+class HistogramWindowingImpl : public Histogram {
+ public:
+  HistogramWindowingImpl();
+  HistogramWindowingImpl(uint64_t num_windows, uint64_t micros_per_window,
+                         uint64_t min_num_per_window);
+
+  HistogramWindowingImpl(const HistogramWindowingImpl&) = delete;
+  HistogramWindowingImpl& operator=(const HistogramWindowingImpl&) = delete;
+
+  ~HistogramWindowingImpl();
+
+  virtual void Clear() override;
+  virtual bool Empty() const override;
+  virtual void Add(uint64_t value) override;
+  virtual void Merge(const Histogram& other) override;
+  void Merge(const HistogramWindowingImpl& other);
+
+  virtual std::string ToString() const override;
+  virtual const char* Name() const override { return "HistogramWindowingImpl"; }
+  virtual uint64_t min() const override { return stats_.min(); }
+  virtual uint64_t max() const override { return stats_.max(); }
+  virtual uint64_t num() const override { return stats_.num(); }
+  virtual double Median() const override;
+  virtual double Percentile(double p) const override;
+  virtual double Average() const override;
+  virtual double StandardDeviation() const override;
+  virtual void Data(HistogramData* const data) const override;
+
+#ifndef NDEBUG
+  void TEST_UpdateClock(const std::shared_ptr<SystemClock>& clock) {
+    clock_ = clock;
+  }
+#endif  // NDEBUG
+
+ private:
+  void TimerTick();
+  void SwapHistoryBucket();
+  inline uint64_t current_window() const {
+    return current_window_.load(std::memory_order_relaxed);
+  }
+  inline uint64_t last_swap_time() const {
+    return last_swap_time_.load(std::memory_order_relaxed);
+  }
+
+  std::shared_ptr<SystemClock> clock_;
+  std::mutex mutex_;
+
+  // Aggregated stats over windows_stats_, all the computation is done
+  // upon aggregated values
+  HistogramStat stats_;
+
+  // This is a circular array representing the latest N time-windows.
+  // Each entry stores a time-window of data. Expiration is done
+  // on window-based.
+  std::unique_ptr<HistogramStat[]> window_stats_;
+
+  std::atomic_uint_fast64_t current_window_;
+  std::atomic_uint_fast64_t last_swap_time_;
+
+  // Following parameters are configuable
+  uint64_t num_windows_ = 5;
+  uint64_t micros_per_window_ = 60000000;
+  // By default, don't care about the number of values in current window
+  // when decide whether to swap windows or not.
+  uint64_t min_num_per_window_ = 0;
+};
+
+}  // namespace ROCKSDB_NAMESPACE