NestedLoopIterator Class Reference

A simple nested loop join, taking in two iterators (left/outer and right/inner) and joining them together. More...

#include <composite_iterators.h>

Inheritance diagram for NestedLoopIterator:

Public Member Functions
	NestedLoopIterator (THD *thd, unique_ptr_destroy_only< RowIterator > source_outer, unique_ptr_destroy_only< RowIterator > source_inner, JoinType join_type, bool pfs_batch_mode)
bool	Init () override
	Initialize or reinitialize the iterator. More...
int	Read () override
	Read a single row. 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	EndPSIBatchModeIfStarted () override
	Ends performance schema batch mode, if started. More...
void	UnlockRow () override
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 void	StartPSIBatchMode ()
	Start performance schema batch mode, if supported (otherwise ignored). More...
virtual RowIterator *	real_iterator ()
	If this iterator is wrapping a different iterator (e.g. More...
virtual const RowIterator *	real_iterator () const

Private Types
enum	{ NEEDS_OUTER_ROW , READING_FIRST_INNER_ROW , READING_INNER_ROWS , END_OF_ROWS }

Private Attributes
enum NestedLoopIterator:: { ... }	m_state
unique_ptr_destroy_only< RowIterator > const	m_source_outer
unique_ptr_destroy_only< RowIterator > const	m_source_inner
const JoinType	m_join_type
const bool	m_pfs_batch_mode
	Whether to use batch mode when scanning the inner iterator. More...

Additional Inherited Members
Protected Member Functions inherited from RowIterator
THD *	thd () const

Detailed Description

A simple nested loop join, taking in two iterators (left/outer and right/inner) and joining them together.

This may, of course, scan the inner iterator many times. It is currently the only form of join we have.

The iterator works as a state machine, where the state records whether we need to read a new outer row or not, and whether we've seen any rows from the inner iterator at all (if not, an outer join need to synthesize a new NULL row).

The iterator takes care of activating performance schema batch mode on the right iterator if needed; this is typically only used if it is the innermost table in the entire join (where the gains from turning on batch mode is the largest, and the accuracy loss from turning it off are the least critical).

Member Enumeration Documentation

anonymous enum

anonymous enum

private

Enumerator
NEEDS_OUTER_ROW
READING_FIRST_INNER_ROW
READING_INNER_ROWS
END_OF_ROWS

Constructor & Destructor Documentation

NestedLoopIterator()

NestedLoopIterator::NestedLoopIterator ( THD *  thd, unique_ptr_destroy_only< RowIterator >  source_outer, unique_ptr_destroy_only< RowIterator >  source_inner, JoinType  join_type, bool  pfs_batch_mode  )

inline

Member Function Documentation

EndPSIBatchModeIfStarted()

void NestedLoopIterator::EndPSIBatchModeIfStarted ( )

inlineoverridevirtual

Ends performance schema batch mode, if started.

It's always safe to call this.

Iterators that have children (composite iterators) must forward the EndPSIBatchModeIfStarted() call to every iterator they could conceivably have called StartPSIBatchMode() on. This ensures that after such a call to on the root iterator, all handlers are out of batch mode.

Reimplemented from RowIterator.

Init()

bool NestedLoopIterator::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 NestedLoopIterator::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.

SetNullRowFlag()

void NestedLoopIterator::SetNullRowFlag ( bool  is_null_row )

inlineoverridevirtual

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).

This is used for outer joins, when an iterator hasn't produced any rows and we need to produce a NULL-complemented row. Init() or Read() won't necessarily reset this flag, so if you ever set is to true, make sure to also set it to false when needed.

Note that this can be called without Init() having been called first. For example, NestedLoopIterator can hit EOF immediately on the outer iterator, which means the inner iterator doesn't get an Init() call, but will still forward SetNullRowFlag to both inner and outer iterators.

TODO: We shouldn't need this. See the comments on AggregateIterator for a bit more discussion on abstracting out a row interface.

Implements RowIterator.

UnlockRow()

void NestedLoopIterator::UnlockRow ( )

inlineoverridevirtual

Implements RowIterator.

Member Data Documentation

m_join_type

const JoinType NestedLoopIterator::m_join_type

private

m_pfs_batch_mode

const bool NestedLoopIterator::m_pfs_batch_mode

private

Whether to use batch mode when scanning the inner iterator.

m_source_inner

unique_ptr_destroy_only<RowIterator> const NestedLoopIterator::m_source_inner

private

m_source_outer

unique_ptr_destroy_only<RowIterator> const NestedLoopIterator::m_source_outer

private

enum { ... } NestedLoopIterator::m_state

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

• sql/iterators/composite_iterators.h
• sql/iterators/composite_iterators.cc