Table_histograms_collection Class Reference

The Table_histograms_collection manages a collection of reference-counted snapshots of histogram statistics (Table_histograms objects) for a table. More...

#include <table_histograms.h>

Public Member Functions
	Table_histograms_collection ()
	Table_histograms_collection (Table_histograms_collection &&)=delete
Table_histograms_collection &	operator= (Table_histograms_collection &&)=delete
	Table_histograms_collection (const Table_histograms_collection &)=delete
Table_histograms_collection &	operator= (const Table_histograms_collection &)=delete
	~Table_histograms_collection ()
const Table_histograms *	acquire ()
	Acquire a pointer to the most recently inserted Table_histograms object. More...
void	release (const Table_histograms *histograms)
	Release a previously acquired Table_histograms object, decreasing its reference count. More...
bool	insert (Table_histograms *histograms)
	Attempt to insert the supplied Table_histograms object into the collection. More...
int	total_reference_count () const
	Count the total number of TABLE objects referencing Table_histograms objects in the collection. More...
size_t	size () const
	Counts the number of Table_histograms objects in the collection. More...

Private Member Functions
void	free_table_histograms (size_t idx)
	Frees a Table_histograms object from the collection and sets its pointer to nullptr. More...

Private Attributes
std::array< Table_histograms *, kMaxNumberOfTableHistogramsInCollection >	m_table_histograms
size_t	m_current_index {0}

Detailed Description

The Table_histograms_collection manages a collection of reference-counted snapshots of histogram statistics (Table_histograms objects) for a table.

It is intended to live on the TABLE_SHARE and provide TABLE objects with reference-counted access to Table_histogram objects through the acquire() and release() methods. The motivation for this class is to decouple the lifetime of histogram statistics from the lifetime of the TABLE_SHARE, so that we avoid having to invalidate the TABLE_SHARE when updating/dropping histograms.

Multiple threads can be opening/closing tables concurrently. Member functions on the Table_histograms_collection should be protected by holding LOCK_open.

When the TABLE_SHARE is initialized and whenever the histograms associated with a table are updated, we create a new Table_histograms object, insert it into the collection, and mark it current.

Constructor & Destructor Documentation

Table_histograms_collection() [1/3]

Table_histograms_collection::Table_histograms_collection

(

)

Table_histograms_collection() [2/3]

Table_histograms_collection::Table_histograms_collection ( Table_histograms_collection &&  )

delete

Table_histograms_collection() [3/3]

Table_histograms_collection::Table_histograms_collection ( const Table_histograms_collection &  )

delete

~Table_histograms_collection()

Table_histograms_collection::~Table_histograms_collection

(

)

Member Function Documentation

acquire()

const Table_histograms * Table_histograms_collection::acquire

(

)

Acquire a pointer to the most recently inserted Table_histograms object.

Increments the reference counter on the returned Table_histograms object.

Returns

Pointer to the current Table_histograms object or nullptr if none exists.

free_table_histograms()

void Table_histograms_collection::free_table_histograms ( size_t  idx )

inlineprivate

Frees a Table_histograms object from the collection and sets its pointer to nullptr.

Parameters

idx	Index of the Table_histograms object to free.

insert()

bool Table_histograms_collection::insert

(

Table_histograms *

histograms

)

Attempt to insert the supplied Table_histograms object into the collection.

The insertion will fail if the collection is full. If the insertion succeeds we mark the object as current and take ownership. The previous current object is deleted if it has a reference count of zero

Parameters

histograms

Pointer to the Table_histograms object to be inserted.

Returns

False if the insertion took place, true otherwise.

operator=() [1/2]

Table_histograms_collection & Table_histograms_collection::operator= ( const Table_histograms_collection &  )

delete

operator=() [2/2]

Table_histograms_collection & Table_histograms_collection::operator= ( Table_histograms_collection &&  )

delete

release()

void Table_histograms_collection::release

(

const Table_histograms *

histograms

)

Release a previously acquired Table_histograms object, decreasing its reference count.

If the reference count of a non-current Table_histograms object reaches zero we delete it. This frees up memory and makes room for a new Table_histograms object in the collection.

Parameters

histograms

Pointer to a Table_histograms object to be released.

size()

size_t Table_histograms_collection::size

(

)

const

Counts the number of Table_histograms objects in the collection.

Primarily used for testing.

Returns

The count of non-null pointers to Table_histograms objects in the collection.

total_reference_count()

int Table_histograms_collection::total_reference_count

(

)

const

Count the total number of TABLE objects referencing Table_histograms objects in the collection.

Primarily used for testing.

Returns

The sum of Table_histogram reference counters. Zero if the collection is empty.

Member Data Documentation

m_current_index

size_t Table_histograms_collection::m_current_index {0}

private

m_table_histograms

std::array<Table_histograms *, kMaxNumberOfTableHistogramsInCollection> Table_histograms_collection::m_table_histograms

private

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

• sql/histograms/table_histograms.h
• sql/histograms/table_histograms.cc