IndexSkipScanIterator Class Reference

#include <index_skip_scan.h>

Inheritance diagram for IndexSkipScanIterator:

Public Member Functions
	IndexSkipScanIterator (THD *thd, TABLE *table, KEY *index_info, uint index, uint eq_prefix_len, uint eq_prefix_key_parts, EQPrefix *eq_prefixes, uint used_key_parts, MEM_ROOT *temp_mem_root, bool has_aggregate_function, uchar *min_range_key, uchar *max_range_key, uchar *min_search_key, uchar *max_search_key, uint range_cond_flag, uint range_key_len)
	Construct new quick select for queries that can do skip scans. More...
	~IndexSkipScanIterator () override
bool	Init () override
	Initialize or reinitialize the iterator. More...
int	Read () override
	Get the next row for skip scan. More...
Public Member Functions inherited from TableRowIterator
	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 ()=default
	RowIterator (const RowIterator &)=delete
	RowIterator (RowIterator &&)=default
virtual const IteratorProfiler *	GetProfiler () const
	Get profiling data for this iterator (for 'EXPLAIN ANALYZE'). More...
virtual void	SetOverrideProfiler (const IteratorProfiler *profiler)
virtual RowIterator *	real_iterator ()
	If this iterator is wrapping a different iterator (e.g. More...
virtual const RowIterator *	real_iterator () const

Private Member Functions
bool	next_eq_prefix ()
	Increments cur_prefix and sets what the next equality prefix should be. More...

Private Attributes
uint	index
KEY *	index_info
MY_BITMAP	column_bitmap
const uint	eq_prefix_len
uint	eq_prefix_key_parts
EQPrefix *	eq_prefixes
uchar *	eq_prefix
uint	max_used_key_length
uint	used_key_parts
uchar *	distinct_prefix
uint	distinct_prefix_len
uint	distinct_prefix_key_parts
MEM_ROOT *	mem_root
const uint	range_key_len
bool	seen_first_key
uchar *const	min_range_key
uchar *const	max_range_key
uchar *const	min_search_key
uchar *const	max_search_key
const uint	range_cond_flag
key_range	start_key
key_range	end_key
bool	has_aggregate_function

Additional Inherited Members
Protected Member Functions inherited from TableRowIterator
int	HandleError (int error)
void	PrintError (int error)
TABLE *	table () const
Protected Member Functions inherited from RowIterator
THD *	thd () const

Constructor & Destructor Documentation

IndexSkipScanIterator()

IndexSkipScanIterator::IndexSkipScanIterator	(	THD *	thd,
		TABLE *	table_arg,
		KEY *	index_info,
		uint	use_index,
		uint	eq_prefix_len,
		uint	eq_prefix_key_parts,
		EQPrefix *	eq_prefixes,
		uint	used_key_parts_arg,
		MEM_ROOT *	return_mem_root,
		bool	has_aggregate_function,
		uchar *	min_range_key_arg,
		uchar *	max_range_key_arg,
		uchar *	min_search_key_arg,
		uchar *	max_search_key_arg,
		uint	range_cond_flag_arg,
		uint	range_key_len_arg
	)

Construct new quick select for queries that can do skip scans.

See get_best_skip_scan() description for more details.

SYNOPSIS IndexSkipScanIterator::IndexSkipScanIterator() table The table being accessed index_info The index chosen for data access use_index The id of index_info range_part The keypart belonging to the range condition C index_range_tree The complete range key eq_prefix_len Length of the equality prefix key eq_prefix_key_parts Number of keyparts in the equality prefix eq_prefixes Array of equality constants (IN list) used_key_parts_arg Total number of keyparts A_1,...,C read_cost_arg Cost of this access method read_records Number of records returned return_mem_root Memory pool for this class

RETURN None

~IndexSkipScanIterator()

IndexSkipScanIterator::~IndexSkipScanIterator ( )

override

Member Function Documentation

Init()

bool IndexSkipScanIterator::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 Index_lookup) and allow you to read the records anew.

Implements RowIterator.

next_eq_prefix()

bool IndexSkipScanIterator::next_eq_prefix ( )

private

Increments cur_prefix and sets what the next equality prefix should be.

SYNOPSIS IndexSkipScanIterator::next_eq_prefix()

DESCRIPTION Increments cur_prefix and sets what the next equality prefix should be. This is done in index order, so the increment happens on the last keypart. The key is written to eq_prefix.

RETURN true OK false No more equality key prefixes.

Read()

int IndexSkipScanIterator::Read ( )

overridevirtual

Get the next row for skip scan.

SYNOPSIS IndexSkipScanIterator::Read()

DESCRIPTION Find the next record in the skip scan. The scan is broken into groups based on distinct A_1,...,B_m. The strategy is to have an outer loop going through all possible A_1,...,A_k. This work is done in next_eq_prefix().

For each equality prefix that we get from "next_eq_prefix() we loop through all distinct B_1,...,B_m within that prefix. And for each of those groups we do a subrange scan on keypart C.

The high level algorithm is like so: for (eq_prefix in eq_prefixes) // (A_1,....A_k) for (distinct_prefix in eq_prefix) // A_1-B_1,...,A_k-B_m do subrange scan within distinct prefix using range_cond // A_1-B_1-C,...A_k-B_m-C

But since this is a iterator interface, state needs to be kept between calls. State is stored in eq_prefix, cur_eq_prefix and distinct_prefix.

NOTES We can be more memory efficient by combining some of these fields. For example, eq_prefix will always be a prefix of distinct_prefix, and distinct_prefix will always be a prefix of min_search_key/max_search_key.

RETURN See RowIterator::Read()

Implements RowIterator.

Member Data Documentation

column_bitmap

MY_BITMAP IndexSkipScanIterator::column_bitmap

private

distinct_prefix

uchar* IndexSkipScanIterator::distinct_prefix

private

distinct_prefix_key_parts

uint IndexSkipScanIterator::distinct_prefix_key_parts

private

distinct_prefix_len

uint IndexSkipScanIterator::distinct_prefix_len

private

end_key

key_range IndexSkipScanIterator::end_key

private

eq_prefix

uchar* IndexSkipScanIterator::eq_prefix

private

eq_prefix_key_parts

uint IndexSkipScanIterator::eq_prefix_key_parts

private

eq_prefix_len

const uint IndexSkipScanIterator::eq_prefix_len

private

eq_prefixes

EQPrefix* IndexSkipScanIterator::eq_prefixes

private

has_aggregate_function

bool IndexSkipScanIterator::has_aggregate_function

private

index

uint IndexSkipScanIterator::index

private

index_info

KEY* IndexSkipScanIterator::index_info

private

max_range_key

uchar* const IndexSkipScanIterator::max_range_key

private

max_search_key

uchar* const IndexSkipScanIterator::max_search_key

private

max_used_key_length

uint IndexSkipScanIterator::max_used_key_length

private

mem_root

MEM_ROOT* IndexSkipScanIterator::mem_root

private

min_range_key

uchar* const IndexSkipScanIterator::min_range_key

private

min_search_key

uchar* const IndexSkipScanIterator::min_search_key

private

range_cond_flag

const uint IndexSkipScanIterator::range_cond_flag

private

range_key_len

const uint IndexSkipScanIterator::range_key_len

private

seen_first_key

bool IndexSkipScanIterator::seen_first_key

private

start_key

key_range IndexSkipScanIterator::start_key

private

used_key_parts

uint IndexSkipScanIterator::used_key_parts

private

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

• sql/range_optimizer/index_skip_scan.h
• sql/range_optimizer/index_skip_scan.cc