YugabyteDB (2.13.1.0-b60, 21121d69985fbf76aa6958d8f04a9bfa936293b5)

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#ifndef YB_UTIL_HDR_HISTOGRAM_H

#define YB_UTIL_HDR_HISTOGRAM_H

// C++ (TR1) port of HdrHistogram.

// Original java implementation: http://giltene.github.io/HdrHistogram/

//

// A High Dynamic Range (HDR) Histogram

//

// HdrHistogram supports the recording and analyzing sampled data value counts

// across a configurable integer value range with configurable value precision

// within the range. Value precision is expressed as the number of significant

// digits in the value recording, and provides control over value quantization

// behavior across the value range and the subsequent value resolution at any

// given level.

//

// For example, a Histogram could be configured to track the counts of observed

// integer values between 0 and 3,600,000,000 while maintaining a value

// precision of 3 significant digits across that range. Value quantization

// within the range will thus be no larger than 1/1,000th (or 0.1%) of any

// value. This example Histogram could be used to track and analyze the counts

// of observed response times ranging between 1 microsecond and 1 hour in

// magnitude, while maintaining a value resolution of 1 microsecond up to 1

// millisecond, a resolution of 1 millisecond (or better) up to one second, and

// a resolution of 1 second (or better) up to 1,000 seconds. At it's maximum

// tracked value (1 hour), it would still maintain a resolution of 3.6 seconds

// (or better).

#include <iosfwd>

#include <memory>

#include "yb/gutil/atomicops.h"

#include "yb/gutil/macros.h"

#include "yb/util/status_fwd.h"

namespace yb {

class AbstractHistogramIterator;

class Status;

class RecordedValuesIterator;

// This implementation allows you to specify a range and accuracy (significant

// digits) to support in an instance of a histogram. The class takes care of

// the rest. At this time, only uint64_t values are supported.

//

// An HdrHistogram consists of a set of buckets, which bucket the magnitude of

// a value stored, and a set of sub-buckets, which implement the tunable

// precision of the storage. So if you specify 3 significant digits of

// precision, then you will get about 10^3 sub-buckets (as a power of 2) for

// each level of magnitude. Magnitude buckets are tracked in powers of 2.

//

// This class is thread-safe.

class HdrHistogram {

 public:

  // Specify the highest trackable value so that the class has a bound on the

  // number of buckets, and # of significant digits (in decimal) so that the

  // class can determine the granularity of those buckets.

  HdrHistogram(uint64_t highest_trackable_value, int num_significant_digits);

  // Copy-construct a (non-consistent) snapshot of other.

  explicit HdrHistogram(const HdrHistogram& other);

  // Validate your params before trying to construct the object.

  static bool IsValidHighestTrackableValue(uint64_t highest_trackable_value);

  static bool IsValidNumSignificantDigits(int num_significant_digits);

  // Record new data.

  void Increment(int64_t value);

  void IncrementBy(int64_t value, int64_t count);

  // Record new data, correcting for "coordinated omission".

  //

  // See https://groups.google.com/d/msg/mechanical-sympathy/icNZJejUHfE/BfDekfBEs_sJ

  // for more details.

  void IncrementWithExpectedInterval(int64_t value,

                                     int64_t expected_interval_between_samples);

  // Fetch configuration params.

  uint64_t highest_trackable_value() const { return highest_trackable_value_; }

  int num_significant_digits() const { return num_significant_digits_; }

  // Get indexes into histogram based on value.

  int BucketIndex(uint64_t value) const;

  int SubBucketIndex(uint64_t value, int bucket_index) const;

  // Count of all events recorded.

  uint64_t TotalCount() const { return base::subtle::NoBarrier_Load(&total_count_); }

  // Count of all events recorded since last Reset. Resets to 0 after

  // ResetPercentiles.

  uint64_t CurrentCount() const {

    return base::subtle::NoBarrier_Load(&current_count_);

  }

  // Sum of all events recorded.

  uint64_t TotalSum() const { return base::subtle::NoBarrier_Load(&total_sum_); }

  // Sum of all events recorded since last Reset. Resets to 0 after

  // ResetPercentiles.

  uint64_t CurrentSum() const {

    return base::subtle::NoBarrier_Load(&current_sum_);

  }

  // Return number of items at index.

  uint64_t CountAt(int bucket_index, int sub_bucket_index) const;

  // Return count of values in bucket with values equivalent to value.

  uint64_t CountInBucketForValue(uint64_t) const;

  // Return representative value based on index.

  static uint64_t ValueFromIndex(int bucket_index, int sub_bucket_index);

  // Get the size (in value units) of the range of values that are equivalent

  // to the given value within the histogram's resolution. Where "equivalent"

  // means that value samples recorded for any two equivalent values are

  // counted in a common total count.

  uint64_t SizeOfEquivalentValueRange(uint64_t value) const;

  // Get the lowest value that is equivalent to the given value within the

  // histogram's resolution. Where "equivalent" means that value samples

  // recorded for any two equivalent values are counted in a common total

  // count.

  uint64_t LowestEquivalentValue(uint64_t value) const;

  // Get the highest value that is equivalent to the given value within the

  // histogram's resolution.

  uint64_t HighestEquivalentValue(uint64_t value) const;

  // Get a value that lies in the middle (rounded up) of the range of values

  // equivalent the given value.

  uint64_t MedianEquivalentValue(uint64_t value) const;

  // Get the next value that is not equivalent to the given value within the

  // histogram's resolution.

  uint64_t NextNonEquivalentValue(uint64_t value) const;

  // Determine if two values are equivalent with the histogram's resolution.

  bool ValuesAreEquivalent(uint64_t value1, uint64_t value2) const;

  // Get the exact minimum value (may lie outside the histogram).

  uint64_t MinValue() const;

  // Get the exact maximum value (may lie outside the histogram).

  uint64_t MaxValue() const;

  // Get the exact mean value of all recorded values in the histogram.

  double MeanValue() const;

  // Get the value at a given percentile.

  // This is a percentile in percents, i.e. 99.99 percentile.

  uint64_t ValueAtPercentile(double percentile) const;

  // Resets the counts_ array to reset the percentiles information.

  // Preserves the values for TotalSum and TotalCount.

  void ResetPercentiles();

  // Get the percentile at a given value

  // TODO: implement

  // double PercentileAtOrBelowValue(uint64_t value) const;

  // Get the count of recorded values within a range of value levels.

  // (inclusive to within the histogram's resolution)

  // TODO: implement

  // uint64_t CountBetweenValues(uint64_t low_value, uint64_t high_value) const;

  // Dump a formatted, multiline string describing this histogram to 'out'.

  void DumpHumanReadable(std::ostream* out) const;

 private:

  friend class AbstractHistogramIterator;

  static const uint64_t kMinHighestTrackableValue = 2;

  static const int kMinValidNumSignificantDigits = 1;

  static const int kMaxValidNumSignificantDigits = 5;

  void Init();

  int CountsArrayIndex(int bucket_index, int sub_bucket_index) const;

  uint64_t highest_trackable_value_;

  int num_significant_digits_;

  int counts_array_length_;

  int bucket_count_;

  int sub_bucket_count_;

  // "Hot" fields in the write path.

  uint8_t sub_bucket_half_count_magnitude_;

  int sub_bucket_half_count_;

  uint32_t sub_bucket_mask_;

  // Also hot.

  // Non-resetting sum and counts.

  base::subtle::Atomic64 total_count_;

  base::subtle::Atomic64 total_sum_;

  // Resetting values

  base::subtle::Atomic64 current_count_;

  base::subtle::Atomic64 current_sum_;

  base::subtle::Atomic64 min_value_;

  base::subtle::Atomic64 max_value_;

  std::unique_ptr<base::subtle::Atomic64[]> counts_;

  HdrHistogram& operator=(const HdrHistogram& other); // Disable assignment operator.

};

// Value returned from iterators.

struct HistogramIterationValue {

  HistogramIterationValue()

    : value_iterated_to(0),

      value_iterated_from(0),

      count_at_value_iterated_to(0),

      count_added_in_this_iteration_step(0),

      total_count_to_this_value(0),

      total_value_to_this_value(0),

      percentile(0.0),

      percentile_level_iterated_to(0.0) {

  }

  void Reset() {

    value_iterated_to = 0;

    value_iterated_from = 0;

    count_at_value_iterated_to = 0;

    count_added_in_this_iteration_step = 0;

    total_count_to_this_value = 0;

    total_value_to_this_value = 0;

    percentile = 0.0;

    percentile_level_iterated_to = 0.0;

  }

  uint64_t value_iterated_to;

  uint64_t value_iterated_from;

  uint64_t count_at_value_iterated_to;

  uint64_t count_added_in_this_iteration_step;

  uint64_t total_count_to_this_value;

  uint64_t total_value_to_this_value;

  double percentile;

  double percentile_level_iterated_to;

};

// Base class for iterating through histogram values.

//

// The underlying histogram must not be modified or destroyed while this class

// is iterating over it.

//

// This class is not thread-safe.

class AbstractHistogramIterator {

 public:

  // Create iterator with new histogram.

  // The histogram must not be mutated while the iterator is in use.

  explicit AbstractHistogramIterator(const HdrHistogram* histogram);

  virtual ~AbstractHistogramIterator() {

  }

  // Returns true if the iteration has more elements.

  virtual bool HasNext() const;

  // Returns the next element in the iteration.

  CHECKED_STATUS Next(HistogramIterationValue* value);

  virtual double PercentileIteratedTo() const;

  virtual double PercentileIteratedFrom() const;

  uint64_t ValueIteratedTo() const;

 protected:

  // Implementations must override these methods.

  virtual void IncrementIterationLevel() = 0;

  virtual bool ReachedIterationLevel() const = 0;

  const HdrHistogram* histogram_;

  HistogramIterationValue cur_iter_val_;

  uint64_t histogram_total_count_;

  int current_bucket_index_;

  int current_sub_bucket_index_;

  uint64_t current_value_at_index_;

  int next_bucket_index_;

  int next_sub_bucket_index_;

  uint64_t next_value_at_index_;

  uint64_t prev_value_iterated_to_;

  uint64_t total_count_to_prev_index_;

  uint64_t total_count_to_current_index_;

  uint64_t total_value_to_current_index_;

  uint64_t count_at_this_value_;

 private:

  bool ExhaustedSubBuckets() const;

  void IncrementSubBucket();

  bool fresh_sub_bucket_;

  DISALLOW_COPY_AND_ASSIGN(AbstractHistogramIterator);

};

// Used for iterating through all recorded histogram values using the finest

// granularity steps supported by the underlying representation. The iteration

// steps through all non-zero recorded value counts, and terminates when all

// recorded histogram values are exhausted.

//

// The underlying histogram must not be modified or destroyed while this class

// is iterating over it.

//

// This class is not thread-safe.

class RecordedValuesIterator : public AbstractHistogramIterator {

 public:

  explicit RecordedValuesIterator(const HdrHistogram* histogram);

 protected:

  virtual void IncrementIterationLevel() override;

  virtual bool ReachedIterationLevel() const override;

 private:

  int visited_sub_bucket_index_;

  int visited_bucket_index_;

  DISALLOW_COPY_AND_ASSIGN(RecordedValuesIterator);

};

// Used for iterating through histogram values according to percentile levels.

// The iteration is performed in steps that start at 0% and reduce their

// distance to 100% according to the percentileTicksPerHalfDistance parameter,

// ultimately reaching 100% when all recorded histogram values are exhausted.

//

// The underlying histogram must not be modified or destroyed while this class

// is iterating over it.

//

// This class is not thread-safe.

class PercentileIterator : public AbstractHistogramIterator {

 public:

  // TODO: Explain percentile_ticks_per_half_distance.

  PercentileIterator(const HdrHistogram* histogram,

                     int percentile_ticks_per_half_distance);

  virtual bool HasNext() const override;

  virtual double PercentileIteratedTo() const override;

  virtual double PercentileIteratedFrom() const override;

 protected:

  virtual void IncrementIterationLevel() override;

  virtual bool ReachedIterationLevel() const override;

 private:

  int percentile_ticks_per_half_distance_;

  double percentile_level_to_iterate_to_;

  double percentile_level_to_iterate_from_;

  bool reached_last_recorded_value_;

  DISALLOW_COPY_AND_ASSIGN(PercentileIterator);

};

} // namespace yb

#endif // YB_UTIL_HDR_HISTOGRAM_H