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#pragma once
#include <util/generic/strbuf.h>
#include <util/generic/vector.h>
#include <util/stream/output.h>
#include <util/system/types.h>
#include <cmath>
namespace NKikimr {
// Helper functions to work with histogram values.
template <typename T>
inline T LoadFrom(const ui8 *storage) {
T val;
std::memcpy(&val, storage, sizeof(T));
return val;
}
template <typename T>
inline void StoreTo(ui8 *storage, T value) {
std::memcpy(storage, &value, sizeof(T));
}
template <typename T>
inline bool CmpEqual(T left, T right) {
return left == right;
}
template <>
inline bool CmpEqual(double left, double right) {
return std::fabs(left - right) < std::numeric_limits<double>::epsilon();
}
template <typename T>
inline bool CmpLess(T left, T right) {
return left < right;
}
// Represents value types supported by histogram.
enum class EHistogramValueType : ui8 { Int16, Int32, Int64, Uint16, Uint32, Uint64, Double, NotSupported };
// Bucket storage size for Equal width histogram.
constexpr const ui32 EqWidthHistogramBucketStorageSize = 8;
// This class represents an `Equal-width` histogram.
// Each bucket represents a range of contiguous values of equal width, and the
// aggregate summary stored in the bucket is the number of rows whose value lies
// within that range.
class TEqWidthHistogram {
public:
#pragma pack(push, 1)
struct TBucket {
// The number of values in a bucket.
ui64 Count{0};
// The `start` value of a bucket, the `end` of the bucket is a next start.
// [start = start[i], end = start[i + 1])
ui8 Start[EqWidthHistogramBucketStorageSize];
};
struct TBucketRange {
ui8 Start[EqWidthHistogramBucketStorageSize];
ui8 End[EqWidthHistogramBucketStorageSize];
};
#pragma pack(pop)
// Have to specify the number of buckets and type of the values.
TEqWidthHistogram(ui32 numBuckets = 1, EHistogramValueType type = EHistogramValueType::Int32);
// From serialized data.
TEqWidthHistogram(const char *str, ui64 size);
// Adds the given `val` to a histogram.
template <typename T>
void AddElement(T val) {
const auto index = FindBucketIndex(val);
// The given `index` in range [0, numBuckets - 1].
const T bucketValue = LoadFrom<T>(Buckets_[index].Start);
if (!index || ((CmpEqual<T>(bucketValue, val) || CmpLess<T>(bucketValue, val)))) {
Buckets_[index].Count++;
} else {
Buckets_[index - 1].Count++;
}
}
// Returns an index of the bucket which stores the given `val`.
// Returned index in range [0, numBuckets - 1].
// Not using `std::lower_bound()` here because need an index to map to `suffix` and `prefix` sum.
template <typename T>
ui32 FindBucketIndex(T val) const {
ui32 start = 0;
ui32 end = GetNumBuckets() - 1;
while (start < end) {
auto it = start + (end - start) / 2;
if (CmpLess<T>(LoadFrom<T>(Buckets_[it].Start), val)) {
start = it + 1;
} else {
end = it;
}
}
return start;
}
// Returns a number of buckets in a histogram.
ui32 GetNumBuckets() const { return Buckets_.size(); }
template <typename T>
ui32 GetBucketWidth() const {
Y_ASSERT(GetNumBuckets());
if (GetNumBuckets() == 1) {
return std::max(static_cast<ui32>(LoadFrom<T>(Buckets_.front().Start)), 1U);
} else {
return std::max(static_cast<ui32>(LoadFrom<T>(Buckets_[1].Start) - LoadFrom<T>(Buckets_[0].Start)), 1U);
}
}
template <>
ui32 GetBucketWidth<double>() const {
return 1;
}
// Returns histogram type.
EHistogramValueType GetType() const { return ValueType_; }
// Returns a number of elements in a bucket by the given `index`.
ui64 GetNumElementsInBucket(ui32 index) const { return Buckets_[index].Count; }
// Initializes buckets with a given `range`.
template <typename T>
void InitializeBuckets(const TBucketRange &range) {
Y_ASSERT(CmpLess<T>(LoadFrom<T>(range.Start), LoadFrom<T>(range.End)));
T rangeLen = LoadFrom<T>(range.End) - LoadFrom<T>(range.Start);
std::memcpy(Buckets_[0].Start, range.Start, sizeof(range.Start));
for (ui32 i = 1; i < GetNumBuckets(); ++i) {
const T prevStart = LoadFrom<T>(Buckets_[i - 1].Start);
StoreTo<T>(Buckets_[i].Start, prevStart + rangeLen);
}
}
// Seriailizes to a binary representation
std::unique_ptr<char> Serialize(ui64 &binSize) const;
// Returns buckets.
const TVector<TBucket> &GetBuckets() const { return Buckets_; }
template <typename T>
void Aggregate(const TEqWidthHistogram &other) {
if ((this->ValueType_ != other.GetType()) || (!BucketsEqual<T>(other))) {
// Should we fail?
return;
}
for (ui32 i = 0; i < Buckets_.size(); ++i) {
Buckets_[i].Count += other.GetBuckets()[i].Count;
}
}
private:
template <typename T>
bool BucketsEqual(const TEqWidthHistogram &other) {
if (Buckets_.size() != other.GetNumBuckets()) {
return false;
}
for (ui32 i = 0; i < Buckets_.size(); ++i) {
if (!CmpEqual<T>(LoadFrom<T>(Buckets_[i].Start), LoadFrom<T>(GetBuckets()[i].Start))) {
return false;
}
}
return true;
}
// Returns binary size of the histogram.
ui64 GetBinarySize(ui32 nBuckets) const;
EHistogramValueType ValueType_;
TVector<TBucket> Buckets_;
};
// This class represents a machinery to estimate a value in a histogram.
class TEqWidthHistogramEstimator {
public:
TEqWidthHistogramEstimator(std::shared_ptr<TEqWidthHistogram> histogram);
// Methods to estimate values.
template <typename T>
ui64 EstimateLessOrEqual(T val) const {
return EstimateOrEqual<T>(val, PrefixSum_);
}
template <typename T>
ui64 EstimateGreaterOrEqual(T val) const {
return EstimateOrEqual<T>(val, SuffixSum_);
}
template <typename T>
ui64 EstimateLess(T val) const {
return EstimateNotEqual<T>(val, PrefixSum_);
}
template <typename T>
ui64 EstimateGreater(T val) const {
return EstimateNotEqual<T>(val, SuffixSum_);
}
template <typename T>
ui64 EstimateEqual(T val) const {
const auto index = Histogram_->FindBucketIndex(val);
// Assuming uniform distribution.
return std::max(1U, static_cast<ui32>(Histogram_->GetNumElementsInBucket(index) / Histogram_->template GetBucketWidth<T>()));
}
// Returns the total number elements in histogram.
// Could be used to adjust scale.
ui64 GetNumElements() const { return PrefixSum_.back(); }
private:
template <typename T>
ui64 EstimateOrEqual(T val, const TVector<ui64> &sumArray) const {
const auto index = Histogram_->FindBucketIndex(val);
return sumArray[index];
}
template <typename T>
ui64 EstimateNotEqual(T val, const TVector<ui64> &sumArray) const {
const auto index = Histogram_->FindBucketIndex(val);
// Take the previous backet if it's not the first one.
if (!index) {
return sumArray[index];
}
return sumArray[index - 1];
}
void CreatePrefixSum(ui32 numBuckets);
void CreateSuffixSum(ui32 numBuckets);
std::shared_ptr<TEqWidthHistogram> Histogram_;
TVector<ui64> PrefixSum_;
TVector<ui64> SuffixSum_;
};
} // namespace NKikimr
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