ReadView Class Reference

Read view lists the trx ids of those transactions for which a consistent read should not see the modifications to the database. More...

#include <read0types.h>

Inheritance diagram for ReadView:

Classes
class	ids_t
	This is similar to a std::vector but it is not a drop in replacement. More...

Public Member Functions
	ReadView ()
	ReadView constructor. More...
	~ReadView () override
	ReadView destructor. More...
bool	changes_visible (trx_id_t id) const override
	Check whether the changes by id are visible. More...
bool	sees_all_trxs_with_id_smaller_or_equal_to (trx_id_t id) const override
	Checks if changes made by each trx with trx->id smaller or equal to id, should be visible to this read view. More...
bool	is_closed () const
void	print (FILE *file) const override
	Describe the read-view. More...
trx_id_t	get_lowest_needed_trx_no () const override
	This read view does not need Undo Logs generated by transactions with trx->no strictly smaller than this value. More...
bool	empty () const
bool	le (const ReadView *rhs) const
Public Member Functions inherited from Read_view_interface
virtual	~Read_view_interface ()=default

Private Member Functions
void	copy_trx_ids (const trx_ids_t &trx_ids)
	Copy the transaction ids from the source vector. More...
void	prepare (trx_id_t id)
	Opens a read view where exactly the transactions serialized before this point in time are seen in the view. More...
void	copy_prepare (const ReadView &other)
	Copy state from another view. More...
void	copy_complete ()
	Complete the copy, insert the creator transaction id into the m_trx_ids too and adjust the m_up_limit_id *, if required. More...
void	creator_trx_id (trx_id_t id)
	Set the creator transaction id, existing id must be 0. More...
	ReadView (const ReadView &)
ReadView &	operator= (const ReadView &)
typedef	UT_LIST_NODE_T (ReadView) node_t

Private Attributes
trx_id_t	m_low_limit_id
	The read should not see any transaction with trx id >= this value. More...
trx_id_t	m_up_limit_id
	The read should see all trx ids which are strictly smaller (<) than this value. More...
trx_id_t	m_creator_trx_id
	If the view is open, then this is a trx->id of the transaction which has created this view, used to let this view see the changes of this transaction. More...
ids_t	m_ids
	Set of RW transactions that was active when this snapshot was taken. More...
trx_id_t	m_low_limit_no
	The view does not need to see the undo logs for transactions whose transaction number is strictly smaller (<) than this value: they can be removed in purge if not needed by other views. More...
std::atomic_bool	m_closed {true}
	False iff this view is in use by a transaction at the moment (is open). More...
byte	pad1 [ut::INNODB_CACHE_LINE_SIZE]
	List of read views in trx_sys. More...
node_t	m_view_list {}

Friends
class	MVCC

Detailed Description

Read view lists the trx ids of those transactions for which a consistent read should not see the modifications to the database.

Constructor & Destructor Documentation

ReadView() [1/2]

ReadView::ReadView

(

)

ReadView constructor.

~ReadView()

ReadView::~ReadView ( )

override

ReadView destructor.

ReadView() [2/2]

ReadView::ReadView ( const ReadView &  )

private

Member Function Documentation

changes_visible()

bool ReadView::changes_visible ( trx_id_t  id ) const

inlineoverridevirtual

Check whether the changes by id are visible.

Parameters

[in]

id

transaction id to check against the view

Returns

whether the view sees the modifications of id.

Implements Read_view_interface.

copy_complete()

void ReadView::copy_complete ( )

inlineprivate

Complete the copy, insert the creator transaction id into the m_trx_ids too and adjust the m_up_limit_id *, if required.

Complete the copy, insert the creator transaction id into the m_ids too and adjust the m_up_limit_id, if required.

copy_prepare()

void ReadView::copy_prepare ( const ReadView &  other )

inlineprivate

Copy state from another view.

Must call copy_complete() to finish.

Parameters

other

view to copy from

copy_trx_ids()

void ReadView::copy_trx_ids ( const trx_ids_t &  trx_ids )

inlineprivate

Copy the transaction ids from the source vector.

creator_trx_id()

void ReadView::creator_trx_id ( trx_id_t  id )

inlineprivate

Set the creator transaction id, existing id must be 0.

empty()

bool ReadView::empty ( ) const

inline

Returns

true if there are no transaction ids in the snapshot

get_lowest_needed_trx_no()

trx_id_t ReadView::get_lowest_needed_trx_no ( ) const

inlineoverridevirtual

This read view does not need Undo Logs generated by transactions with trx->no strictly smaller than this value.

Returns

safe estimate of the lowest value of TRX_UNDO_TRX_NO header in Undo Logs still needed to support this read view

Implements Read_view_interface.

is_closed()

bool ReadView::is_closed ( ) const

inline

Returns

true if the view is closed

le()

bool ReadView::le ( const ReadView *  rhs ) const

inline

Parameters

rhs	view to compare with

Returns

true if this view is less than or equal rhs

operator=()

ReadView & ReadView::operator= ( const ReadView &  )

private

prepare()

void ReadView::prepare ( trx_id_t  id )

inlineprivate

Opens a read view where exactly the transactions serialized before this point in time are seen in the view.

Parameters

id	Creator transaction id

print()

void ReadView::print ( FILE *  file ) const

inlineoverridevirtual

Describe the read-view.

Parameters

[in]

file

file to write to

Implements Read_view_interface.

sees_all_trxs_with_id_smaller_or_equal_to()

bool ReadView::sees_all_trxs_with_id_smaller_or_equal_to ( trx_id_t  id ) const

inlineoverridevirtual

Checks if changes made by each trx with trx->id smaller or equal to id, should be visible to this read view.

Conceptually equivalent to: forall x<=id . changes_visible(x).

Parameters

[in]

id

max transaction id to check

Returns

true if view sees all transactions with smaller or equal id

Implements Read_view_interface.

UT_LIST_NODE_T()

typedef ReadView::UT_LIST_NODE_T ( ReadView  )

private

Friends And Related Function Documentation

MVCC

friend class MVCC

friend

Member Data Documentation

m_closed

std::atomic_bool ReadView::m_closed {true}

private

False iff this view is in use by a transaction at the moment (is open).

m_creator_trx_id

trx_id_t ReadView::m_creator_trx_id

private

If the view is open, then this is a trx->id of the transaction which has created this view, used to let this view see the changes of this transaction.

Note that a transaction might have no trx->id assigned in which case this will be 0. A transaction may also get trx->id assigned after it has already created a read view, in which case it should call set_view_creator_trx_id to update this field. It is 0 for read views cloned by clone_oldest_view. Otherwise its value doesn't matter.

m_ids

ids_t ReadView::m_ids

private

Set of RW transactions that was active when this snapshot was taken.

m_low_limit_id

trx_id_t ReadView::m_low_limit_id

private

The read should not see any transaction with trx id >= this value.

In other words, this is the "high water mark".

m_low_limit_no

trx_id_t ReadView::m_low_limit_no

private

The view does not need to see the undo logs for transactions whose transaction number is strictly smaller (<) than this value: they can be removed in purge if not needed by other views.

m_up_limit_id

trx_id_t ReadView::m_up_limit_id

private

The read should see all trx ids which are strictly smaller (<) than this value.

In other words, this is the low water mark".

m_view_list

node_t ReadView::m_view_list {}

private

pad1

byte ReadView::pad1[ut::INNODB_CACHE_LINE_SIZE]

private

List of read views in trx_sys.

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

• storage/innobase/include/read0types.h
• storage/innobase/read/read0read.cc