histograms::Value_map_base Class Reference

The abstract base class for all Value_map types. More...

#include <value_map.h>

Inheritance diagram for histograms::Value_map_base:

Public Member Functions
	Value_map_base (const CHARSET_INFO *charset, Value_map_type data_type)
virtual	~Value_map_base ()=default
virtual size_t	size () const =0
	Returns the number of [value, count] pairs in the Value_map. More...
template<class T >
bool	add_values (const T &value, const ha_rows count)
	Add a value with the given count to this Value_map. More...
void	add_null_values (const ha_rows count)
	Increase the number of null values with the given count. More...
ha_rows	get_num_null_values () const
virtual Histogram *	build_histogram (MEM_ROOT *mem_root, size_t num_buckets, const std::string &db_name, const std::string &tbl_name, const std::string &col_name) const =0
	Create a Histogram from this Value_map. More...
double	get_sampling_rate () const
void	set_sampling_rate (double sampling_rate)
	Set the sampling rate that was used to generate this Value_map. More...
const CHARSET_INFO *	get_character_set () const
Value_map_type	get_data_type () const
virtual size_t	element_overhead () const =0

Protected Attributes
MEM_ROOT	m_mem_root

Private Attributes
double	m_sampling_rate
const CHARSET_INFO *	m_charset
ha_rows	m_num_null_values
const Value_map_type	m_data_type

Detailed Description

The abstract base class for all Value_map types.

We would ideally like to have only one class for the Value map concept (no inheritance) which would gives us an easier interface. But there are some reasons for why we need to to split the class into a non-templated base class and a templated subclass:

• We are collecting Value_maps in a collection/vector where they have a different template type. This cannot be achieved unless we have a non-templated base class.
• When working on a collection of Value_maps, it is more convenient to declare the interface in the base class (Value_map_base) so that we don't need to do a cast to the subclass in order to get hold of the methods we want to use.
• Value_map_base::add_values and Value_map::add_values looks like the same function, but they are not. Value_map_base::add_values is a small functions that helps us cast the Value_map<T> to the correct type (for instance Value_map<longlong>). Ideally, this function would have been pure virtual, but it's not possible to have virtual member function templates.

Constructor & Destructor Documentation

Value_map_base()

histograms::Value_map_base::Value_map_base	(	const CHARSET_INFO *	charset,
		Value_map_type	data_type
	)

~Value_map_base()

virtual histograms::Value_map_base::~Value_map_base ( )

virtualdefault

Member Function Documentation

add_null_values()

void histograms::Value_map_base::add_null_values ( const ha_rows  count )

inline

Increase the number of null values with the given count.

Parameters

count

The number of null values.

add_values()

template<class T >

template bool histograms::Value_map_base::add_values	(	const T &	value,
		const ha_rows	count
	)

Add a value with the given count to this Value_map.

If the given value already exists, the count will be added to the existing count.

Parameters

value	The value to add.
count	Count of the value to add.

Returns

false on success, and true in case of errors (OOM).

build_histogram()

virtual Histogram * histograms::Value_map_base::build_histogram ( MEM_ROOT *  mem_root, size_t  num_buckets, const std::string &  db_name, const std::string &  tbl_name, const std::string &  col_name  ) const

pure virtual

Create a Histogram from this Value_map.

The resulting histogram will have at most "num_buckets" buckets (might be less), and all of its contents will be allocated on the supplied MEM_ROOT.

Parameters

mem_root	The MEM_ROOT to allocate the contents on
num_buckets	Maximum number of buckets to create
db_name	Database name
tbl_name	Table name
col_name	Column name

Returns

nullptr on error, or a valid histogram if success.

Implemented in histograms::Value_map< T >.

element_overhead()

virtual size_t histograms::Value_map_base::element_overhead ( ) const

pure virtual

Returns

the overhead in bytes for each distinct value stored in the Value_map.

Implemented in histograms::Value_map< T >.

get_character_set()

const CHARSET_INFO * histograms::Value_map_base::get_character_set ( ) const

inline

Returns

the character set for the data this Value_map contains

get_data_type()

Value_map_type histograms::Value_map_base::get_data_type ( ) const

inline

Returns

the data type that this Value_map contains

get_num_null_values()

ha_rows histograms::Value_map_base::get_num_null_values ( ) const

inline

Returns

The number of null values in this Value_map.

get_sampling_rate()

double histograms::Value_map_base::get_sampling_rate ( ) const

inline

Returns

The sampling rate that was used to generate this Value_map.

set_sampling_rate()

void histograms::Value_map_base::set_sampling_rate ( double  sampling_rate )

inline

Set the sampling rate that was used to generate this Value_map.

Parameters

sampling_rate

The sampling rate.

size()

virtual size_t histograms::Value_map_base::size ( ) const

pure virtual

Returns the number of [value, count] pairs in the Value_map.

Returns

The number of values in the Value_map.

Implemented in histograms::Value_map< T >.

Member Data Documentation

m_charset

const CHARSET_INFO* histograms::Value_map_base::m_charset

private

m_data_type

const Value_map_type histograms::Value_map_base::m_data_type

private

m_mem_root

MEM_ROOT histograms::Value_map_base::m_mem_root

protected

m_num_null_values

ha_rows histograms::Value_map_base::m_num_null_values

private

m_sampling_rate

double histograms::Value_map_base::m_sampling_rate

private

---

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

• sql/histograms/value_map.h
• sql/histograms/value_map.cc