MVCC Class Reference

The MVCC read view manager. More...

#include <read0read.h>

Public Member Functions
	MVCC (ulint size)
	Constructor. More...
	~MVCC ()
	Destructor. More...
void	view_open (ReadView *&view, trx_t *trx)
	Allocate and create a view. More...
void	view_close (ReadView *&view, bool own_mutex)
	Close a view created by the above function. More...
void	clone_oldest_view (ReadView *view)
	Clones the oldest view into the provided view, unless the function determines that the provided view is already a good enough lower bound. More...
ulint	size () const

Static Public Member Functions
static bool	is_view_active (ReadView *view)
static void	set_view_creator_trx_id (ReadView *view, trx_id_t id)
	Set the view creator transaction id. More...

Private Member Functions
bool	validate () const
	Validates a read view list. More...
ReadView *	get_view ()
	Find a free view from the active list, if none found then allocate a new view. More...
	MVCC (const MVCC &)
MVCC &	operator= (const MVCC &)
typedef	UT_LIST_BASE_NODE_T (ReadView, m_view_list) view_list_t

Private Attributes
view_list_t	m_free
	Free views ready for reuse. More...
view_list_t	m_views
	Active and closed views, the closed views will have the creator trx id set to TRX_ID_MAX. More...

Detailed Description

The MVCC read view manager.

Constructor & Destructor Documentation

MVCC() [1/2]

MVCC::MVCC ( ulint  size )

explicit

Constructor.

Parameters

size	Number of views to pre-allocate

~MVCC()

MVCC::~MVCC

(

)

Destructor.

Free all the views in the m_free list

MVCC() [2/2]

MVCC::MVCC ( const MVCC &  )

private

Member Function Documentation

clone_oldest_view()

void MVCC::clone_oldest_view

(

ReadView *

view

)

Clones the oldest view into the provided view, unless the function determines that the provided view is already a good enough lower bound.

The caller owns the view that is passed in, which is interpreted to be a previous lower bound known to the caller. No need to call view_close(view,..).

Note: This function is called by Purge to determine the purge_sys->view used to distinguish which transactions are considered committed by everybody, and thus their undo logs can be purged. Purge mainly uses purge_sys->view->low_limit_no(), which is a safe lower-bound on what can be purged based on NO, and further limits it to the lowest needed NO reported by GTID Persistor. But other places like ROLLBACK use purge_sys->view->changes_visible(ID,..).

Parameters

[in,out]

view

Preallocated view, owned by the caller. Can be either default constructed (m_low_limit_no is 0) or a fully initialized ReadView object.

get_view()

ReadView * MVCC::get_view ( )

inlineprivate

Find a free view from the active list, if none found then allocate a new view.

This function will also attempt to move delete marked views from the active list to the freed list.

Returns

a view to use

a view to use

is_view_active()

static bool MVCC::is_view_active ( ReadView *  view )

inlinestatic

Returns

true if the view is active and valid

operator=()

MVCC & MVCC::operator= ( const MVCC &  )

private

set_view_creator_trx_id()

static void MVCC::set_view_creator_trx_id ( ReadView *  view, trx_id_t  id  )

inlinestatic

Set the view creator transaction id.

Note: This should be set only for views created by RW transactions.

Parameters

view	Set the creator trx id for this view
id	Transaction id to set

size()

ulint MVCC::size

(

)

const

Returns

the number of active views

UT_LIST_BASE_NODE_T()

typedef MVCC::UT_LIST_BASE_NODE_T ( ReadView  , m_view_list    )

private

validate()

bool MVCC::validate ( ) const

private

Validates a read view list.

view_close()

void MVCC::view_close	(	ReadView *&	view,
		bool	own_mutex
	)

Close a view created by the above function.

Parameters

view	view allocated by trx_open.
own_mutex	true if caller owns trx_sys_t::mutex

view_open()

void MVCC::view_open	(	ReadView *&	view,
		trx_t *	trx
	)

Allocate and create a view.

Parameters

view	View owned by this class created for the caller. Must be freed by calling view_close()
trx	Transaction instance of caller

If no new RW transaction has been started since the last view was created then reuse the the existing view.

Member Data Documentation

m_free

view_list_t MVCC::m_free

private

Free views ready for reuse.

m_views

view_list_t MVCC::m_views

private

Active and closed views, the closed views will have the creator trx id set to TRX_ID_MAX.

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

• storage/innobase/include/read0read.h
• storage/innobase/read/read0read.cc