Record_buffer Class Reference

This class represents a buffer that can be used for multi-row reads. More...

#include <record_buffer.h>

Public Member Functions
	Record_buffer (ha_rows records, size_t record_size, uchar *buffer)
	Create a new record buffer with the specified size. More...
ha_rows	max_records () const
	Get the number of records that can be stored in the buffer. More...
size_t	record_size () const
	Get the amount of space allocated for each record in the buffer. More...
ha_rows	records () const
	Get the number of records currently stored in the buffer. More...
uchar *	record (ha_rows pos) const
	Get the buffer that holds the record on position pos. More...
uchar *	add_record ()
	Add a new record at the end of the buffer. More...
void	remove_last ()
	Remove the record that was last added to the buffer. More...
void	clear ()
	Clear the buffer. More...
void	reset ()
	Reset the buffer. More...
void	set_out_of_range (bool val)
	Set whether the end of the range was reached while filling the buffer. More...
bool	is_out_of_range () const
	Check if the end of the range was reached while filling the buffer. More...

Static Public Member Functions
static constexpr size_t	buffer_size (ha_rows records, size_t record_size)
	This function calculates how big the uchar buffer provided to Record_buffer's constructor must be, given a number of records and the record size. More...

Private Attributes
ha_rows	m_max_records
	The maximum number of records that can be stored in the buffer. More...
size_t	m_record_size
	The number of bytes available for each record. More...
ha_rows	m_count = 0
	The number of records currently stored in the buffer. More...
uchar *	m_buffer
	The uchar buffer that holds the records. More...
bool	m_out_of_range = false
	Tells if end-of-range was found while filling the buffer. More...

Detailed Description

This class represents a buffer that can be used for multi-row reads.

It is allocated by the executor and given to the storage engine through the handler, using handler::ha_set_record_buffer(), so that the storage engine can fill the buffer with multiple rows in a single read call.

For now, the record buffer is only used internally by the storage engine as a prefetch cache. The storage engine fills the record buffer when the executor requests the first record, but it returns a single record only to the executor. If the executor wants to access the records in the buffer, it has to call a handler function such as handler::ha_index_next() or handler::ha_rnd_next(). Then the storage engine will copy the next record from the record buffer to the memory area specified in the arguments of the handler function, typically TABLE::record[0].

Constructor & Destructor Documentation

Record_buffer()

Record_buffer::Record_buffer ( ha_rows  records, size_t  record_size, uchar *  buffer  )

inline

Create a new record buffer with the specified size.

Parameters

records	the number of records that can be stored in the buffer
record_size	the size of each record
buffer	the uchar buffer that will hold the records (its size should be at least Record_buffer::buffer_size(records, record_size))

Member Function Documentation

add_record()

uchar * Record_buffer::add_record ( )

inline

Add a new record at the end of the buffer.

Returns

the uchar buffer of the added record

buffer_size()

static constexpr size_t Record_buffer::buffer_size ( ha_rows  records, size_t  record_size  )

inlinestaticconstexpr

This function calculates how big the uchar buffer provided to Record_buffer's constructor must be, given a number of records and the record size.

Parameters

records	the maximum number of records in the buffer
record_size	the size of each record

Returns

the total number of bytes needed for all the records

clear()

void Record_buffer::clear ( )

inline

Clear the buffer.

Remove all the records. The end-of-range flag is preserved.

is_out_of_range()

bool Record_buffer::is_out_of_range ( ) const

inline

Check if the end of the range was reached while filling the buffer.

Return values

true	if the end range was reached
false	if the scan is still within the range

max_records()

ha_rows Record_buffer::max_records ( ) const

inline

Get the number of records that can be stored in the buffer.

Returns

the maximum number of records in the buffer

record()

uchar * Record_buffer::record ( ha_rows  pos ) const

inline

Get the buffer that holds the record on position pos.

Parameters

pos	the record number (must be smaller than records())

Returns

the uchar buffer that holds the specified record

record_size()

size_t Record_buffer::record_size ( ) const

inline

Get the amount of space allocated for each record in the buffer.

Returns

the record size

records()

ha_rows Record_buffer::records ( ) const

inline

Get the number of records currently stored in the buffer.

Returns

the number of records stored in the buffer

remove_last()

void Record_buffer::remove_last ( )

inline

Remove the record that was last added to the buffer.

reset()

void Record_buffer::reset ( void  )

inline

Reset the buffer.

Remove all records and clear the end-of-range flag.

set_out_of_range()

void Record_buffer::set_out_of_range ( bool  val )

inline

Set whether the end of the range was reached while filling the buffer.

Parameters

val	true if end of range was reached, false if still within range

Member Data Documentation

m_buffer

uchar* Record_buffer::m_buffer

private

The uchar buffer that holds the records.

m_count

ha_rows Record_buffer::m_count = 0

private

The number of records currently stored in the buffer.

m_max_records

ha_rows Record_buffer::m_max_records

private

The maximum number of records that can be stored in the buffer.

m_out_of_range

bool Record_buffer::m_out_of_range = false

private

Tells if end-of-range was found while filling the buffer.

m_record_size

size_t Record_buffer::m_record_size

private

The number of bytes available for each record.

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

• sql/record_buffer.h