MySQL  8.0.20
Source Code Documentation
CacheInvalidatorIterator Class Referencefinal

An iterator that helps invalidating caches. More...

#include <composite_iterators.h>

Inheritance diagram for CacheInvalidatorIterator:
RowIterator

Public Member Functions

 CacheInvalidatorIterator (THD *thd, unique_ptr_destroy_only< RowIterator > source_iterator, const std::string &name)
 
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 UnlockRow () override
 
std::vector< std::string > DebugString () const override
 Returns a short string (used for EXPLAIN FORMAT=tree) with user-readable information for this iterator. More...
 
std::vector< Childchildren () const override
 List of zero or more iterators which are direct children of this one. More...
 
int64_t generation () const
 
std::string name () const
 
- Public Member Functions inherited from RowIterator
 RowIterator (THD *thd)
 
virtual ~RowIterator ()
 
virtual std::string TimingString () const
 
JOINjoin_for_explain () const
 
void set_join_for_explain (JOIN *join)
 
virtual void StartPSIBatchMode ()
 Start performance schema batch mode, if supported (otherwise ignored). More...
 
virtual void EndPSIBatchModeIfStarted ()
 Ends performance schema batch mode, if started. More...
 
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
 

Private Attributes

unique_ptr_destroy_only< RowIteratorm_source_iterator
 
int64_t m_generation = 0
 
std::string m_name
 

Additional Inherited Members

- Protected Member Functions inherited from RowIterator
THDthd () const
 

Detailed Description

An iterator that helps invalidating caches.

Every time a row passes through it or it changes state in any other way, it increments its “generation” counter. This allows MaterializeIterator to see whether any of its dependencies has changed, and then force a rematerialization – this is typically used for LATERAL tables, where we're joining in a derived table that depends on something earlier in the join.

Constructor & Destructor Documentation

◆ CacheInvalidatorIterator()

CacheInvalidatorIterator::CacheInvalidatorIterator ( THD thd,
unique_ptr_destroy_only< RowIterator source_iterator,
const std::string &  name 
)
inline

Member Function Documentation

◆ children()

std::vector<Child> CacheInvalidatorIterator::children ( ) const
inlineoverridevirtual

List of zero or more iterators which are direct children of this one.

By convention, if there are multiple ones (ie., we're doing a join), the outer iterator is listed first. So for a LEFT JOIN b, we'd list a before b.

Reimplemented from RowIterator.

◆ DebugString()

vector< string > CacheInvalidatorIterator::DebugString ( ) const
overridevirtual

Returns a short string (used for EXPLAIN FORMAT=tree) with user-readable information for this iterator.

When implementing these, try to avoid internal jargon (e.g. “eq_ref”); prefer things that read like normal, technical English (e.g. “single-row index lookup”).

For certain complex operations, such as MaterializeIterator, there can be multiple strings. If so, they are interpreted as nested operations, with the outermost, last-done operation first and the other ones indented as if they were child iterators.

Callers should use FullDebugString() below, which adds costs (see set_estimated_cost() etc.) if present.

Implements RowIterator.

◆ generation()

int64_t CacheInvalidatorIterator::generation ( ) const
inline

◆ Init()

bool CacheInvalidatorIterator::Init ( )
inlineoverridevirtual

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.

◆ name()

std::string CacheInvalidatorIterator::name ( ) const
inline

◆ Read()

int CacheInvalidatorIterator::Read ( )
inlineoverridevirtual

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 CacheInvalidatorIterator::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 CacheInvalidatorIterator::UnlockRow ( )
inlineoverridevirtual

Implements RowIterator.

Member Data Documentation

◆ m_generation

int64_t CacheInvalidatorIterator::m_generation = 0
private

◆ m_name

std::string CacheInvalidatorIterator::m_name
private

◆ m_source_iterator

unique_ptr_destroy_only<RowIterator> CacheInvalidatorIterator::m_source_iterator
private

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