MySQL  8.0.19
Source Code Documentation
TableRowIterator Class Reference

#include <row_iterator.h>

Inheritance diagram for TableRowIterator:
RowIterator ConstIterator DynamicRangeIterator EQRefIterator FollowTailIterator FullTextSearchIterator IndexRangeScanIterator IndexScanIterator< Reverse > MaterializedTableFunctionIterator MaterializeIterator MultiRangeRowIterator PushedJoinRefIterator RefIterator< Reverse > RefOrNullIterator SortBufferIndirectIterator SortBufferIterator< Packed_addon_fields > SortBufferIterator< false > SortBufferIterator< true > SortFileIndirectIterator SortFileIterator< Packed_addon_fields > SortFileIterator< false > SortFileIterator< true > StreamingIterator TableScanIterator TemptableAggregateIterator

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 ()
 
virtual bool Init ()=0
 Initialize or reinitialize the iterator. More...
 
virtual int Read ()=0
 Read a single row. More...
 
virtual std::vector< Childchildren () const
 List of zero or more iterators which are direct children of this one. More...
 
virtual std::vector< std::string > DebugString () const =0
 Returns a short string (used for EXPLAIN FORMAT=tree) with user-readable information for this iterator. More...
 
virtual std::string TimingString () const
 
JOINjoin_for_explain () const
 
void set_join_for_explain (JOIN *join)
 
void set_estimated_cost (double estimated_cost)
 
double estimated_cost () const
 
void set_expected_rows (double expected_rows)
 
double expected_rows () const
 
virtual RowIteratorreal_iterator ()
 If this iterator is wrapping a different iterator (e.g. More...
 
virtual const RowIteratorreal_iterator () const
 

Protected Member Functions

int HandleError (int error)
 
void PrintError (int error)
 
TABLEtable () const
 
- Protected Member Functions inherited from RowIterator
THDthd () 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 SortFileIterator< false >, SortFileIterator< true >, SortBufferIterator< false >, and SortBufferIterator< true >.

Friends And Related Function Documentation

◆ AlternativeIterator

friend class AlternativeIterator
friend

Member Data Documentation

◆ m_table

TABLE* const TableRowIterator::m_table
private

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