#include <row0pread-histogram.h>

Public Member Functions
	Histogram_sampler (size_t max_threads, int sampling_seed, double sampling_percentage, enum_sampling_method sampling_method)
	Constructor. More...

	~Histogram_sampler ()
	Destructor. More...

bool	init (trx_t trx, dict_index_t index, row_prebuilt_t *prebuilt)
	Initialize the sampler context. More...

dberr_t	buffer_next ()
	Buffer next row. More...

void	buffer_end ()
	End parallel read in case the reader thread is still active and wait for its exit. More...

void	set (byte *buf)
	Set the buffer. More...

dberr_t	run ()
	Start the sampling process. More...

bool	skip ()
	Check if the processing of the record needs to be skipped. More...

Private Member Functions
void	wait_for_start_of_buffering ()
	Wait till there is a request to buffer the next row. More...

void	wait_for_end_of_buffering ()
	Wait till the buffering of the row is complete. More...

void	signal_start_of_buffering ()
	Signal that the next row needs to be buffered. More...

void	signal_end_of_buffering ()
	Signal that the buffering of the row is complete. More...

void	set_error_state (dberr_t err)
	Set the error state. More...

bool	is_error_set () const

dberr_t	start_callback (Parallel_reader::Thread_ctx *reader_thread_ctx)
	Each parallel reader thread's init function. More...

dberr_t	finish_callback (Parallel_reader::Thread_ctx *reader_thread_ctx)
	Each parallel reader thread's end function. More...

dberr_t	sample_rec (const Parallel_reader::Ctx ctx, const rec_t rec, ulint offsets, const dict_index_t index, row_prebuilt_t *prebuilt)
	Convert the row in InnoDB format to MySQL format and store in the buffer for server to use. More...

dberr_t	process_non_leaf_rec (const Parallel_reader::Ctx ctx, row_prebuilt_t prebuilt)
	For each record in a non-leaf block at level 1 (if leaf level is 0) check if the child page needs to be sampled and if so sample all the rows in the child page. More...

dberr_t	process_leaf_rec (const Parallel_reader::Ctx ctx, row_prebuilt_t prebuilt)
	Process the record in the leaf page. More...

Private Attributes
byte *	m_buf {nullptr}
	Buffer to store the sampled row which is in the MySQL format. More...

os_event_t	m_start_buffer_event
	Event to notify if the next row needs to be buffered. More...

os_event_t	m_end_buffer_event
	Event to notify if the next row has been buffered. More...

dberr_t	m_err {DB_SUCCESS}
	Error code when the row was buffered. More...

Parallel_reader	m_parallel_reader
	The parallel reader. More...

std::mt19937	m_random_generator
	Random generator engine used to provide us random uniformly distributed values required to decide if the row in question needs to be sampled or not. More...

enum_sampling_method	m_sampling_method {enum_sampling_method::NONE}
	Sampling method to be used for sampling. More...

double	m_sampling_percentage {}
	Sampling percentage to be used for sampling. More...

int	m_sampling_seed {}
	Sampling seed to be used for sampling. More...

std::atomic_size_t	m_n_sampled
	Number of rows sampled. More...

Static Private Attributes
static std::uniform_real_distribution< double >	m_distribution
	Uniform distribution used by the random generator. More...

Constructor & Destructor Documentation

◆ Histogram_sampler()

Histogram_sampler::Histogram_sampler	(	size_t	max_threads,
		int	sampling_seed,
		double	sampling_percentage,
		enum_sampling_method	sampling_method
	)

explicit

Constructor.

Parameters

[in]	max_threads	Maximum number of threads to use.
[in]	sampling_seed	seed to be used for sampling
[in]	sampling_percentage	percentage of sampling that needs to be done
[in]	sampling_method	sampling method to be used for sampling

◆ ~Histogram_sampler()

Histogram_sampler::~Histogram_sampler ( )

Destructor.

Member Function Documentation

◆ buffer_end()

void Histogram_sampler::buffer_end ( )

End parallel read in case the reader thread is still active and wait for its exit.

This can happen if we're ending sampling prematurely.

◆ buffer_next()

dberr_t Histogram_sampler::buffer_next ( )

Buffer next row.

Returns: error code

◆ finish_callback()

dberr_t Histogram_sampler::finish_callback ( Parallel_reader::Thread_ctx * reader_thread_ctx )

private

Each parallel reader thread's end function.

Parameters

[in] reader_thread_ctx context information related to the thread

Returns: DB_SUCCESS or error code.

◆ init()

bool Histogram_sampler::init	(	trx_t *	trx,
		dict_index_t *	index,
		row_prebuilt_t *	prebuilt
	)

Initialize the sampler context.

Parameters

[in]	trx	Transaction used for parallel read.
[in]	index	clustered index.
[in]	prebuilt	prebuilt info

Return values

true	on success.

◆ is_error_set()

bool Histogram_sampler::is_error_set ( ) const

inlineprivate

Returns: true if in error state.

◆ process_leaf_rec()

dberr_t Histogram_sampler::process_leaf_rec	(	const Parallel_reader::Ctx *	ctx,
		row_prebuilt_t *	prebuilt
	)

private

Process the record in the leaf page.

This would happen only when the root page is the leaf page and in such a case we process the page regardless of the sampling percentage.

Parameters

[in]	ctx	Parallel read context.
[in]	prebuilt	Row meta-data cache.

Returns: error code

◆ process_non_leaf_rec()

dberr_t Histogram_sampler::process_non_leaf_rec	(	const Parallel_reader::Ctx *	ctx,
		row_prebuilt_t *	prebuilt
	)

private

For each record in a non-leaf block at level 1 (if leaf level is 0) check if the child page needs to be sampled and if so sample all the rows in the child page.

Parameters

[in]	ctx	Parallel read context.
[in]	prebuilt	Row meta-data cache.

Returns: error code

◆ run()

dberr_t Histogram_sampler::run ( )

Start the sampling process.

Returns: DB_SUCCESS or error code.

◆ sample_rec()

dberr_t Histogram_sampler::sample_rec	(	const Parallel_reader::Ctx *	ctx,
		const rec_t *	rec,
		ulint *	offsets,
		const dict_index_t *	index,
		row_prebuilt_t *	prebuilt
	)

private

Convert the row in InnoDB format to MySQL format and store in the buffer for server to use.

Parameters

[in]	ctx	Parallel read context.
[in]	rec	record that needs to be converted
[in]	offsets	offsets belonging to the record
[in]	index	index of the record
[in]	prebuilt	Row meta-data cache.

Returns: DB_SUCCESS or error code.

◆ set()

void Histogram_sampler::set ( byte * buf )

inline

Set the buffer.

Parameters

[in] buf buffer to be used to store the row converted to MySQL format.

◆ set_error_state()

void Histogram_sampler::set_error_state ( dberr_t err )

inlineprivate

Set the error state.

Parameters

[in] err Error state to set to.

◆ signal_end_of_buffering()

void Histogram_sampler::signal_end_of_buffering ( )

private

Signal that the buffering of the row is complete.

◆ signal_start_of_buffering()

void Histogram_sampler::signal_start_of_buffering ( )

private

Signal that the next row needs to be buffered.

◆ skip()

bool Histogram_sampler::skip ( )

Check if the processing of the record needs to be skipped.

In case of record belonging to non-leaf page, we decide if the child page pertaining to the record needs to be skipped. In case of record belonging to leaf page, we read the page regardless.

Returns: true if it needs to be skipped, else false.

◆ start_callback()

dberr_t Histogram_sampler::start_callback ( Parallel_reader::Thread_ctx * reader_thread_ctx )

private

Each parallel reader thread's init function.

Parameters

[in] reader_thread_ctx context information related to the thread

Returns: DB_SUCCESS or error code.

There are data members in row_prebuilt_t that cannot be accessed in multi-threaded mode e.g., blob_heap.

row_prebuilt_t is designed for single threaded access and to share it among threads is not recommended unless "you know what you are doing". This is very fragile code as it stands.

To solve the blob heap issue in prebuilt we request parallel reader thread to use blob heap per thread and we pass this blob heap to the InnoDB to MySQL row format conversion function.

◆ wait_for_end_of_buffering()

void Histogram_sampler::wait_for_end_of_buffering ( )

private

Wait till the buffering of the row is complete.

◆ wait_for_start_of_buffering()

void Histogram_sampler::wait_for_start_of_buffering ( )

private

Wait till there is a request to buffer the next row.

Member Data Documentation

◆ m_buf

byte* Histogram_sampler::m_buf {nullptr}

private

Buffer to store the sampled row which is in the MySQL format.

◆ m_distribution

std::uniform_real_distribution< double > Histogram_sampler::m_distribution

staticprivate

Uniform distribution used by the random generator.

◆ m_end_buffer_event

os_event_t Histogram_sampler::m_end_buffer_event

private

Event to notify if the next row has been buffered.

◆ m_err

dberr_t Histogram_sampler::m_err {DB_SUCCESS}

private

Error code when the row was buffered.

◆ m_n_sampled

std::atomic_size_t Histogram_sampler::m_n_sampled

private

Number of rows sampled.

◆ m_parallel_reader

Parallel_reader Histogram_sampler::m_parallel_reader

private

The parallel reader.

◆ m_random_generator

std::mt19937 Histogram_sampler::m_random_generator

private

Random generator engine used to provide us random uniformly distributed values required to decide if the row in question needs to be sampled or not.

◆ m_sampling_method

enum_sampling_method Histogram_sampler::m_sampling_method {enum_sampling_method::NONE}

private

Sampling method to be used for sampling.

◆ m_sampling_percentage

double Histogram_sampler::m_sampling_percentage {}

private

Sampling percentage to be used for sampling.

◆ m_sampling_seed

int Histogram_sampler::m_sampling_seed {}

private

Sampling seed to be used for sampling.

◆ m_start_buffer_event

os_event_t Histogram_sampler::m_start_buffer_event

private

Event to notify if the next row needs to be buffered.

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

storage/innobase/include/row0pread-histogram.h
storage/innobase/row/row0pread-histogram.cc

Public Member Functions

Private Member Functions

Private Attributes

Static Private Attributes

Constructor & Destructor Documentation

◆ Histogram_sampler()

◆ ~Histogram_sampler()

Member Function Documentation

◆ buffer_end()

◆ buffer_next()

◆ finish_callback()

◆ init()

◆ is_error_set()

◆ process_leaf_rec()

◆ process_non_leaf_rec()

◆ run()

◆ sample_rec()

◆ set()

◆ set_error_state()

◆ signal_end_of_buffering()

◆ signal_start_of_buffering()

◆ skip()

◆ start_callback()

◆ wait_for_end_of_buffering()

◆ wait_for_start_of_buffering()

Member Data Documentation

◆ m_buf

◆ m_distribution

◆ m_end_buffer_event

◆ m_err

◆ m_n_sampled

◆ m_parallel_reader

◆ m_random_generator

◆ m_sampling_method

◆ m_sampling_percentage

◆ m_sampling_seed

◆ m_start_buffer_event