TableRowIterator Class Reference

#include <row_iterator.h>

Inheritance diagram for TableRowIterator:

Public Member Functions
	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 bool	Init ()=0
	Initialize or reinitialize the iterator. More...
virtual int	Read ()=0
	Read a single row. More...
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

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

Private Attributes
TABLE *const	m_table

Friends
class	AlternativeIterator

Constructor & Destructor Documentation

TableRowIterator()

TableRowIterator::TableRowIterator ( THD *  thd, TABLE *  table  )

inline

Member Function Documentation

EndPSIBatchModeIfStarted()

void TableRowIterator::EndPSIBatchModeIfStarted ( )

overridevirtual

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.

HandleError()

int TableRowIterator::HandleError ( int  error )

protected

PrintError()

void TableRowIterator::PrintError ( int  error )

protected

SetNullRowFlag()

void TableRowIterator::SetNullRowFlag ( bool  is_null_row )

overridevirtual

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.

StartPSIBatchMode()

void TableRowIterator::StartPSIBatchMode ( )

overridevirtual

Start performance schema batch mode, if supported (otherwise ignored).

PFS batch mode is a mitigation to reduce the overhead of performance schema, typically applied at the innermost table of the entire join. If you start it before scanning the table and then end it afterwards, the entire set of handler calls will be timed only once, as a group, and the costs will be distributed evenly out. This reduces timer overhead.

If you start PFS batch mode, you must also take care to end it at the end of the scan, one way or the other. Do note that this is true even if the query ends abruptly (LIMIT is reached, or an error happens). The easiest workaround for this is to simply call EndPSIBatchModeIfStarted() on the root iterator at the end of the scan. See the PFSBatchMode class for a useful helper.

The rules for starting batch and ending mode are:

1. If you are an iterator with exactly one child (FilterIterator etc.), forward any StartPSIBatchMode() calls to it.
2. If you drive an iterator (read rows from it using a for loop or similar), use PFSBatchMode as described above.
3. If you have multiple children, ignore the call and do your own handling of batch mode as appropriate. For materialization, #2 would typically apply. For joins, it depends on the join type (e.g., NestedLoopIterator applies batch mode only when scanning the innermost table).

The upshot of this is that when scanning a single table, batch mode will typically be activated for that table (since we call StartPSIBatchMode() on the root iterator, and it will trickle all the way down to the table iterator), but for a join, the call will be ignored and the join iterator will activate batch mode by itself as needed.

Reimplemented from RowIterator.

table()

TABLE * TableRowIterator::table ( ) const

inlineprotected

UnlockRow()

void TableRowIterator::UnlockRow ( )

overridevirtual

The default implementation of unlock-row method of RowIterator, used in all access methods except EQRefIterator.

Implements RowIterator.

Reimplemented in IndexRangeScanIterator.

Friends And Related Function Documentation

AlternativeIterator

friend class AlternativeIterator

friend

Member Data Documentation

m_table

TABLE* const TableRowIterator::m_table

private

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

• sql/iterators/row_iterator.h
• sql/iterators/basic_row_iterators.cc