MySQL 8.0.31
Source Code Documentation
DeleteRowsIterator Class Referencefinal

An iterator that deletes all rows returned by its child iterator. More...

#include <delete_rows_iterator.h>

Inheritance diagram for DeleteRowsIterator:
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Public Member Functions

 DeleteRowsIterator (THD *thd, unique_ptr_destroy_only< RowIterator > source, JOIN *join, table_map tables_to_delete_from, table_map immediate_tables)
 
bool Init () override
 Initialize or reinitialize the iterator. More...
 
int Read () override
 Read a single 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...
 
void SetNullRowFlag (bool) 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 UnlockRow () override
 
- Public Member Functions inherited from RowIterator
 RowIterator (THD *thd)
 
virtual ~RowIterator ()=default
 
 RowIterator (const RowIterator &)=delete
 
 RowIterator (RowIterator &&)=default
 
virtual const IteratorProfilerGetProfiler () const
 Get profiling data for this iterator (for 'EXPLAIN ANALYZE'). More...
 
virtual void SetOverrideProfiler ([[maybe_unused]] const IteratorProfiler *profiler)
 
virtual RowIteratorreal_iterator ()
 If this iterator is wrapping a different iterator (e.g. More...
 
virtual const RowIteratorreal_iterator () const
 

Private Member Functions

bool DoImmediateDeletesAndBufferRowIds ()
 Perform all the immediate deletes for the current row returned by the join, and buffer row IDs for the non-immediate tables. More...
 
bool DoDelayedDeletes ()
 Perform all the delayed deletes. More...
 
bool DoDelayedDeletesFromTable (TABLE *table)
 Perform all the delayed deletes for the given table. More...
 

Private Attributes

unique_ptr_destroy_only< RowIteratorm_source
 The iterator producing the rows to delete. More...
 
JOINm_join
 The join producing the rows to delete. More...
 
table_map m_tables_to_delete_from
 The tables to delete from. More...
 
table_map m_immediate_tables
 The tables to delete from immediately while scanning the join result. More...
 
table_map m_hash_join_tables
 All the tables that are part of a hash join. More...
 
table_map m_transactional_tables {0}
 The target tables that live in transactional storage engines. More...
 
table_map m_tables_with_before_triggers {0}
 The target tables that have before delete triggers. More...
 
table_map m_tables_with_after_triggers {0}
 The target tables that have after delete triggers. More...
 
Mem_root_array< unique_ptr_destroy_only< Unique > > m_tempfiles
 Temporary files holding row IDs to delete after the scan of the join result is complete. More...
 
Mem_root_array< TABLE * > m_delayed_tables
 The tables to delete from after the scan of the join result is complete. More...
 
ha_rows m_deleted_rows {0}
 The number of rows that have been deleted. More...
 
bool m_has_delayed_deletes {false}
 True if any row ID has been stored in one of the m_tempfiles. More...
 

Additional Inherited Members

- Protected Member Functions inherited from RowIterator
THDthd () const
 

Detailed Description

An iterator that deletes all rows returned by its child iterator.

Constructor & Destructor Documentation

◆ DeleteRowsIterator()

DeleteRowsIterator::DeleteRowsIterator ( THD thd,
unique_ptr_destroy_only< RowIterator source,
JOIN join,
table_map  tables_to_delete_from,
table_map  immediate_tables 
)

Member Function Documentation

◆ DoDelayedDeletes()

bool DeleteRowsIterator::DoDelayedDeletes ( )
private

Perform all the delayed deletes.

◆ DoDelayedDeletesFromTable()

bool DeleteRowsIterator::DoDelayedDeletesFromTable ( TABLE table)
private

Perform all the delayed deletes for the given table.

◆ DoImmediateDeletesAndBufferRowIds()

bool DeleteRowsIterator::DoImmediateDeletesAndBufferRowIds ( )
private

Perform all the immediate deletes for the current row returned by the join, and buffer row IDs for the non-immediate tables.

◆ EndPSIBatchModeIfStarted()

void DeleteRowsIterator::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 DeleteRowsIterator::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 TABLE_REF) and allow you to read the records anew.

Implements RowIterator.

◆ Read()

int DeleteRowsIterator::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
0OK
-1End of records
1Error

Implements RowIterator.

◆ SetNullRowFlag()

void DeleteRowsIterator::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.

◆ StartPSIBatchMode()

void DeleteRowsIterator::StartPSIBatchMode ( )
inlineoverridevirtual

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.

◆ UnlockRow()

void DeleteRowsIterator::UnlockRow ( )
inlineoverridevirtual

Implements RowIterator.

Member Data Documentation

◆ m_delayed_tables

Mem_root_array<TABLE *> DeleteRowsIterator::m_delayed_tables
private

The tables to delete from after the scan of the join result is complete.

◆ m_deleted_rows

ha_rows DeleteRowsIterator::m_deleted_rows {0}
private

The number of rows that have been deleted.

◆ m_has_delayed_deletes

bool DeleteRowsIterator::m_has_delayed_deletes {false}
private

True if any row ID has been stored in one of the m_tempfiles.

◆ m_hash_join_tables

table_map DeleteRowsIterator::m_hash_join_tables
private

All the tables that are part of a hash join.

We use this map to find out how to get the row ID from a table when buffering row IDs for delayed delete. For those tables that are part of a hash join, the row ID will already be available in handler::ref, and calling handler::position() will overwrite it with an incorrect row ID (most likely the last row read from the table). For those that are not part of a hash join, handler::position() must be called to get the current row ID from the underlying scan.

◆ m_immediate_tables

table_map DeleteRowsIterator::m_immediate_tables
private

The tables to delete from immediately while scanning the join result.

◆ m_join

JOIN* DeleteRowsIterator::m_join
private

The join producing the rows to delete.

◆ m_source

unique_ptr_destroy_only<RowIterator> DeleteRowsIterator::m_source
private

The iterator producing the rows to delete.

◆ m_tables_to_delete_from

table_map DeleteRowsIterator::m_tables_to_delete_from
private

The tables to delete from.

◆ m_tables_with_after_triggers

table_map DeleteRowsIterator::m_tables_with_after_triggers {0}
private

The target tables that have after delete triggers.

◆ m_tables_with_before_triggers

table_map DeleteRowsIterator::m_tables_with_before_triggers {0}
private

The target tables that have before delete triggers.

◆ m_tempfiles

Mem_root_array<unique_ptr_destroy_only<Unique> > DeleteRowsIterator::m_tempfiles
private

Temporary files holding row IDs to delete after the scan of the join result is complete.

◆ m_transactional_tables

table_map DeleteRowsIterator::m_transactional_tables {0}
private

The target tables that live in transactional storage engines.


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