ClickHouse/base/poco/Foundation/include/Poco/HashStatistic.h

//
// HashStatistic.h
//
// Library: Foundation
// Package: Hashing
// Module:  HashStatistic
//
// Definition of the HashStatistic class.
//
// Copyright (c) 2006, Applied Informatics Software Engineering GmbH.
// and Contributors.
//
// SPDX-License-Identifier:	BSL-1.0
//


#ifndef Foundation_HashStatistic_INCLUDED
#define Foundation_HashStatistic_INCLUDED


#include <vector>
#include "Poco/Foundation.h"


namespace Poco
{


//@ deprecated
class Foundation_API HashStatistic
/// HashStatistic class bundles statistical information on the current state of a HashTable
{
public:
    HashStatistic(
        UInt32 tableSize, UInt32 numEntries, UInt32 numZeroEntries, UInt32 maxEntry, std::vector<UInt32> details = std::vector<UInt32>());
    /// Creates the HashStatistic.

    virtual ~HashStatistic();
    /// Destroys the HashStatistic.

    UInt32 maxPositionsOfTable() const;
    /// Returns the maximum number of different hash values possible for the table

    UInt32 numberOfEntries() const;
    /// Returns the total number of entries currently stored in the HashTable

    UInt32 numberOfZeroPositions() const;
    /// Returns the number of hash positions that contain no entry.

    double avgEntriesPerHash() const;
    /// Returns the average number of entries per position in the Hashtable, the higher this value the less efficient
    /// performs hashing. If a large value is returned and getNumberOfZeroPositions also returns a large value, this
    /// indicates an inefficient hashing function. If the number of zero entries is low, resizing the HashTable, should
    /// be enough to improve performance

    double avgEntriesPerHashExclZeroEntries() const;
    /// Same as getAvgEntriesPerHash but hash values that contain no entry are ignored,
    /// getAvgEntriesPerHashExclZeroEntries >= getAvgEntriesPerHash will always be true.

    UInt32 maxEntriesPerHash() const;
    /// Returns the maximum number of entries per hash value found in the current table.

    const std::vector<UInt32> detailedEntriesPerHash() const;
    /// Will either be an empty vector or will contain for each possible hash value, the number of entries currently stored

    std::string toString() const;
    /// Converts the whole data structure into a string.

private:
    UInt32 _sizeOfTable;
    UInt32 _numberOfEntries;
    UInt32 _numZeroEntries;
    UInt32 _maxEntriesPerHash;
    std::vector<UInt32> _detailedEntriesPerHash;
};


inline UInt32 HashStatistic::maxPositionsOfTable() const
{
    return _sizeOfTable;
}


inline UInt32 HashStatistic::numberOfEntries() const
{
    return _numberOfEntries;
}


inline UInt32 HashStatistic::numberOfZeroPositions() const
{
    return _numZeroEntries;
}


inline double HashStatistic::avgEntriesPerHash() const
{
    return ((double)numberOfEntries()) / maxPositionsOfTable();
}


inline double HashStatistic::avgEntriesPerHashExclZeroEntries() const
{
    return ((double)numberOfEntries()) / (maxPositionsOfTable() - numberOfZeroPositions());
}


inline UInt32 HashStatistic::maxEntriesPerHash() const
{
    return _maxEntriesPerHash;
}


inline const std::vector<UInt32> HashStatistic::detailedEntriesPerHash() const
{
    return _detailedEntriesPerHash;
}


} // namespace Poco


#endif // Foundation_HashStatistic_INCLUDED