Equi-height bucket. More...

#include <equi_height_bucket.h>

Public Member Functions
	Bucket (T lower, T upper, double freq, ha_rows num_distinct)
	Equi-height bucket constructor. More...

const T &	get_lower_inclusive () const

const T &	get_upper_inclusive () const

double	get_cumulative_frequency () const

ha_rows	get_num_distinct () const

bool	bucket_to_json (Json_array *json_array) const
	Convert this equi-height bucket to a JSON array. More...

double	get_distance_from_lower (const T &value) const
	Finds the relative location of "value" between bucket endpoints. More...

double	get_distance_from_upper (const T &value) const
	Returns the fraction of all elements between bucket endpoints [a, b] that are strictly greater than "value". More...

double	get_distance_from_lower (const double &value) const

double	get_distance_from_lower (const String &value) const
	An attempt to calculate the distance for string values. More...

double	get_distance_from_lower (const MYSQL_TIME &value) const

double	get_distance_from_lower (const my_decimal &value) const

double	get_distance_from_upper (const longlong &value) const

double	get_distance_from_upper (const ulonglong &value) const

Private Member Functions
bool	add_values_json_bucket (const double &lower_value, const double &upper_value, Json_array *json_array)

bool	add_values_json_bucket (const String &lower_value, const String &upper_value, Json_array *json_array)

bool	add_values_json_bucket (const ulonglong &lower_value, const ulonglong &upper_value, Json_array *json_array)

bool	add_values_json_bucket (const longlong &lower_value, const longlong &upper_value, Json_array *json_array)

bool	add_values_json_bucket (const MYSQL_TIME &lower_value, const MYSQL_TIME &upper_value, Json_array *json_array)

bool	add_values_json_bucket (const my_decimal &lower_value, const my_decimal &upper_value, Json_array *json_array)

Static Private Member Functions
static bool	add_values_json_bucket (const T &lower_value, const T &upper_value, Json_array *json_array)
	Add values to a JSON bucket. More...

Private Attributes
const T	m_lower_inclusive
	Lower inclusive value contained in this bucket. More...

const T	m_upper_inclusive
	Upper inclusive value contained in this bucket. More...

const double	m_cumulative_frequency
	The cumulative frequency. 0.0 <= m_cumulative_frequency <= 1.0. More...

const ha_rows	m_num_distinct
	Number of distinct values in this bucket. More...

Detailed Description

template<class T>
class histograms::equi_height::Bucket< T >

Equi-height bucket.

Constructor & Destructor Documentation

◆ Bucket()

template<typename T >

histograms::equi_height::Bucket< T >::Bucket	(	T	lower,
		T	upper,
		double	freq,
		ha_rows	num_distinct
	)

Equi-height bucket constructor.

Does nothing more than setting the member variables.

Parameters

lower	Lower inclusive value.
upper	Upper inclusive value.
freq	The cumulative frequency.
num_distinct	Number of distinct values in this bucket.

Member Function Documentation

◆ add_values_json_bucket() [1/7]

bool histograms::equi_height::Bucket< double >::add_values_json_bucket	(	const double &	lower_value,
		const double &	upper_value,
		Json_array *	json_array
	)

private

◆ add_values_json_bucket() [2/7]

bool histograms::equi_height::Bucket< longlong >::add_values_json_bucket	(	const longlong &	lower_value,
		const longlong &	upper_value,
		Json_array *	json_array
	)

private

◆ add_values_json_bucket() [3/7]

bool histograms::equi_height::Bucket< my_decimal >::add_values_json_bucket	(	const my_decimal &	lower_value,
		const my_decimal &	upper_value,
		Json_array *	json_array
	)

private

◆ add_values_json_bucket() [4/7]

bool histograms::equi_height::Bucket< MYSQL_TIME >::add_values_json_bucket	(	const MYSQL_TIME &	lower_value,
		const MYSQL_TIME &	upper_value,
		Json_array *	json_array
	)

private

◆ add_values_json_bucket() [5/7]

bool histograms::equi_height::Bucket< String >::add_values_json_bucket	(	const String &	lower_value,
		const String &	upper_value,
		Json_array *	json_array
	)

private

◆ add_values_json_bucket() [6/7]

template<class T >

static bool histograms::equi_height::Bucket< T >::add_values_json_bucket	(	const T &	lower_value,
		const T &	upper_value,
		Json_array *	json_array
	)

staticprivate

Add values to a JSON bucket.

This function adds the lower and upper inclusive value to the supplied JSON array. The lower value is added first.

Parameters

	lower_value	The lower inclusive value to add.
	upper_value	The upper inclusive value to add.
[out]	json_array	A JSON array where the bucket data is stored.

Returns: True on error, false otherwise.

◆ add_values_json_bucket() [7/7]

bool histograms::equi_height::Bucket< ulonglong >::add_values_json_bucket	(	const ulonglong &	lower_value,
		const ulonglong &	upper_value,
		Json_array *	json_array
	)

private

◆ bucket_to_json()

template<typename T >

bool histograms::equi_height::Bucket< T >::bucket_to_json ( Json_array * json_array ) const

Convert this equi-height bucket to a JSON array.

This function will take the contents of the current equi-height bucket and put it in the output parameter "json_array". The result is an array with the following contents: Index 0: Lower inclusive value. Index 1: Upper inclusive value. Index 2: Cumulative frequency. Index 3: Number of distinct values.

Parameters

[out] json_array Output where the bucket content is to be stored.

Returns: True on error, false otherwise.

◆ get_cumulative_frequency()

template<class T >

double histograms::equi_height::Bucket< T >::get_cumulative_frequency ( ) const

inline

Returns: Cumulative frequency.

◆ get_distance_from_lower() [1/5]

double histograms::equi_height::Bucket< double >::get_distance_from_lower ( const double & value ) const

◆ get_distance_from_lower() [2/5]

double histograms::equi_height::Bucket< my_decimal >::get_distance_from_lower ( const my_decimal & value ) const

◆ get_distance_from_lower() [3/5]

double histograms::equi_height::Bucket< MYSQL_TIME >::get_distance_from_lower ( const MYSQL_TIME & value ) const

◆ get_distance_from_lower() [4/5]

double histograms::equi_height::Bucket< String >::get_distance_from_lower ( const String & value ) const

An attempt to calculate the distance for string values.

It goes like this:

First we transform the lower inclusive value, the upper inclusive value and the query value (COLUMN = "query value") using the method "my_strnxfrm". The result of "my_strnfxfrm" is a transformed string that gives us the correct sort order by using "memcmp" on the transformed values. For example, the strings "110", "120" and "130" in utf8mb4_0900_ai_ci gives us the following byte values:

"110": 28 62 28 62 28 61 "120": 28 63 28 63 28 61 "130": 28 64 28 64 28 61

We then find the common prefix for these three transformed strings, which is the byte value 28 in this case. We remove this, and ends up with the following:

"110": 62 28 62 28 61 "120": 63 28 63 28 61 "130": 64 28 64 28 61

The reason for removing the common prefix is that if the eight first byte values are the same, the next step will fail.

We then make a 8-byte unsigned integer representation for each of these values by concatenating together all the byte values.

See also: uchar_array_to_64bit_unsigned

If the eight first bytes were equal, we would end up with equal values here. Do this for all three, and with these values we can find out the distance from the lower inclusive value to the "query value". Note that this will NOT be 100% accurate, but it will gives us a rough estimate (and a far better estimate than nothing at all).

Parameters

value The value to calculate the distance for.

Returns: The distance, between 0.0 and 1.0 inclusive.

◆ get_distance_from_lower() [5/5]

template<class T >

double histograms::equi_height::Bucket< T >::get_distance_from_lower ( const T & value ) const

Finds the relative location of "value" between bucket endpoints.

This is used to determine the fraction of a bucket to include in selectivity estimates in the case where the query value lies inside a bucket.

get_distance_from_lower returns the fraction of all elements between bucket endpoints [a, b] that lie in the interval [a, value), i.e., strictly less than value. For some histogram types the return value is only an estimate.

Parameters

value The value to calculate the distance for.

Returns: The distance between "value" and lower inclusive value.

◆ get_distance_from_upper() [1/3]

double histograms::equi_height::Bucket< longlong >::get_distance_from_upper ( const longlong & value ) const

◆ get_distance_from_upper() [2/3]

template<class T >

double histograms::equi_height::Bucket< T >::get_distance_from_upper ( const T & value ) const

Returns the fraction of all elements between bucket endpoints [a, b] that are strictly greater than "value".

For some histogram types the return value is only an estimate.

Returns: The distance between "value" and upper inclusive value.

◆ get_distance_from_upper() [3/3]

double histograms::equi_height::Bucket< ulonglong >::get_distance_from_upper ( const ulonglong & value ) const

◆ get_lower_inclusive()

template<class T >

const T & histograms::equi_height::Bucket< T >::get_lower_inclusive ( ) const

inline

Returns: Lower inclusive value.

◆ get_num_distinct()

template<class T >

ha_rows histograms::equi_height::Bucket< T >::get_num_distinct ( ) const

inline

Returns: Number of distinct values.

◆ get_upper_inclusive()

template<class T >

const T & histograms::equi_height::Bucket< T >::get_upper_inclusive ( ) const

inline

Returns: Upper inclusive value.

Member Data Documentation

◆ m_cumulative_frequency

template<class T >

const double histograms::equi_height::Bucket< T >::m_cumulative_frequency

private

The cumulative frequency. 0.0 <= m_cumulative_frequency <= 1.0.

◆ m_lower_inclusive

template<class T >

const T histograms::equi_height::Bucket< T >::m_lower_inclusive

private

Lower inclusive value contained in this bucket.

◆ m_num_distinct

template<class T >

const ha_rows histograms::equi_height::Bucket< T >::m_num_distinct

private

Number of distinct values in this bucket.

◆ m_upper_inclusive

template<class T >

const T histograms::equi_height::Bucket< T >::m_upper_inclusive

private

Upper inclusive value contained in this bucket.

The documentation for this class was generated from the following files:

sql/histograms/equi_height.h
sql/histograms/equi_height_bucket.h
sql/histograms/equi_height_bucket.cc

Public Member Functions

Private Member Functions

Static Private Member Functions

Private Attributes

Detailed Description

Constructor & Destructor Documentation

◆ Bucket()

Member Function Documentation

◆ add_values_json_bucket() [1/7]

◆ add_values_json_bucket() [2/7]

◆ add_values_json_bucket() [3/7]

◆ add_values_json_bucket() [4/7]

◆ add_values_json_bucket() [5/7]

◆ add_values_json_bucket() [6/7]

◆ add_values_json_bucket() [7/7]

◆ bucket_to_json()

◆ get_cumulative_frequency()

◆ get_distance_from_lower() [1/5]

◆ get_distance_from_lower() [2/5]

◆ get_distance_from_lower() [3/5]

◆ get_distance_from_lower() [4/5]

◆ get_distance_from_lower() [5/5]

◆ get_distance_from_upper() [1/3]

◆ get_distance_from_upper() [2/3]

◆ get_distance_from_upper() [3/3]

◆ get_lower_inclusive()

◆ get_num_distinct()

◆ get_upper_inclusive()

Member Data Documentation

◆ m_cumulative_frequency

◆ m_lower_inclusive

◆ m_num_distinct

◆ m_upper_inclusive