PushedJoinRefIterator Class Reference

Read a table assumed to be included in execution of a pushed join. More...

#include <ref_row_iterators.h>

Inheritance diagram for PushedJoinRefIterator:

Public Member Functions
	PushedJoinRefIterator (THD *thd, TABLE *table, Index_lookup *ref, bool use_order, bool is_unique, ha_rows *examined_rows)
bool	Init () override
	Initialize or reinitialize the iterator. More...
int	Read () override
	Read a single row. More...
Public Member Functions inherited from TableRowIterator
	TableRowIterator (THD *thd, TABLE *table)
void	UnlockRow () override
	The default implementation of unlock-row method of RowIterator, used in all access methods except EQRefIterator. More...
void	SetNullRowFlag (bool is_null_row) override
	Mark the current row buffer as containing a NULL row or not, so that if you read from it and the flag is true, you'll get only NULLs no matter what is actually in the buffer (typically some old leftover row). More...
void	StartPSIBatchMode () override
	Start performance schema batch mode, if supported (otherwise ignored). More...
void	EndPSIBatchModeIfStarted () override
	Ends performance schema batch mode, if started. More...
Public Member Functions inherited from RowIterator
	RowIterator (THD *thd)
virtual	~RowIterator ()=default
	RowIterator (const RowIterator &)=delete
	RowIterator (RowIterator &&)=default
virtual const IteratorProfiler *	GetProfiler () const
	Get profiling data for this iterator (for 'EXPLAIN ANALYZE'). More...
virtual void	SetOverrideProfiler ([[maybe_unused]] const IteratorProfiler *profiler)
virtual RowIterator *	real_iterator ()
	If this iterator is wrapping a different iterator (e.g. More...
virtual const RowIterator *	real_iterator () const

Private Attributes
Index_lookup *const	m_ref
const bool	m_use_order
const bool	m_is_unique
bool	m_first_record_since_init
ha_rows *const	m_examined_rows

Additional Inherited Members
Protected Member Functions inherited from TableRowIterator
int	HandleError (int error)
void	PrintError (int error)
TABLE *	table () const
Protected Member Functions inherited from RowIterator
THD *	thd () const

Detailed Description

Read a table assumed to be included in execution of a pushed join.

This is the counterpart of RefIterator / EQRefIterator for child tables in a pushed join. As the underlying handler interface for pushed joins are the same for Ref / EQRef operations, we implement both in the same PushedJoinRefIterator class.

In order to differentiate between a 'range' and 'single-row lookup' in the DebugString(), the class takes a 'bool Unique' C'tor argument. This also offers some optimizations in implementation of Read().

When the table access is performed as part of the pushed join, all 'linked' child columns are prefetched together with the parent row. The handler will then only format the row as required by MySQL and set table status accordingly.

However, there may be situations where the prepared pushed join was not executed as assumed. It is the responsibility of the handler to handle these situation by letting ha_index_read_pushed() then effectively do a plain old' index_read_map(..., HA_READ_KEY_EXACT);

Constructor & Destructor Documentation

PushedJoinRefIterator()

PushedJoinRefIterator::PushedJoinRefIterator	(	THD *	thd,
		TABLE *	table,
		Index_lookup *	ref,
		bool	use_order,
		bool	is_unique,
		ha_rows *	examined_rows
	)

Member Function Documentation

Init()

bool PushedJoinRefIterator::Init ( )

overridevirtual

Initialize or reinitialize the iterator.

You must always call Init() before trying a Read() (but Init() does not imply Read()).

You can call Init() multiple times; subsequent calls will rewind the iterator (or reposition it, depending on whether the iterator takes in e.g. a Index_lookup) and allow you to read the records anew.

Implements RowIterator.

Read()

int PushedJoinRefIterator::Read ( )

overridevirtual

Read a single row.

The row data is not actually returned from the function; it is put in the table's (or tables', in case of a join) record buffer, ie., table->records[0].

Return values

0	OK
-1	End of records
1	Error

Implements RowIterator.

Member Data Documentation

m_examined_rows

ha_rows* const PushedJoinRefIterator::m_examined_rows

private

m_first_record_since_init

bool PushedJoinRefIterator::m_first_record_since_init

private

m_is_unique

const bool PushedJoinRefIterator::m_is_unique

private

m_ref

Index_lookup* const PushedJoinRefIterator::m_ref

private

m_use_order

const bool PushedJoinRefIterator::m_use_order

private

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

• sql/iterators/ref_row_iterators.h
• sql/iterators/ref_row_iterators.cc