cost_model.h File Reference

#include "my_base.h"
#include "sql/join_optimizer/access_path.h"
#include "sql/join_optimizer/relational_expression.h"
#include "sql/mem_root_array.h"

Go to the source code of this file.

Classes
struct	FilterCost
	See EstimateFilterCost. More...

Functions
void	AddCost (THD *thd, const ContainedSubquery &subquery, double num_rows, FilterCost *cost)
	Used internally by EstimateFilterCost() only. More...
FilterCost	EstimateFilterCost (THD *thd, double num_rows, Item *condition, const Query_block *outer_query_block)
	Estimate the cost of evaluating “condition”, “num_rows” times. More...
FilterCost	EstimateFilterCost (THD *thd, double num_rows, const Mem_root_array< ContainedSubquery > &contained_subqueries)
	A cheaper overload of EstimateFilterCost() that assumes that all contained subqueries have already been extracted (ie., it skips the walking, which can be fairly expensive). More...
double	EstimateCostForRefAccess (THD *thd, TABLE *table, unsigned key_idx, double num_output_rows)
void	EstimateSortCost (AccessPath *path)
void	EstimateMaterializeCost (THD *thd, AccessPath *path)
void	EstimateAggregateCost (AccessPath *path, const Query_block *query_block, std::string *trace=nullptr)
	Estimate costs and result row count for an aggregate operation. More...
void	EstimateDeleteRowsCost (AccessPath *path)
void	EstimateUpdateRowsCost (AccessPath *path)
void	EstimateStreamCost (AccessPath *path)
	Estimate the costs and row count for a STREAM AccessPath. More...
void	EstimateLimitOffsetCost (AccessPath *path)
	Estimate the costs and row count for a LIMIT_OFFSET AccessPath. More...
double	FindOutputRowsForJoin (double left_rows, double right_rows, const JoinPredicate *edge)

Variables
constexpr size_t	kMaxItemLengthEstimate = 4096
	When we make cost estimates, we use this as the maximal length the values we get from evaluating an Item (in bytes). More...
constexpr double	kApplyOneFilterCost = 0.1
constexpr double	kAggregateOneRowCost = 0.1
constexpr double	kSortOneRowCost = 0.1
constexpr double	kHashBuildOneRowCost = 0.1
constexpr double	kHashProbeOneRowCost = 0.1
constexpr double	kHashReturnOneRowCost = 0.07
constexpr double	kMaterializeOneRowCost = 0.1
constexpr double	kWindowOneRowCost = 0.1
constexpr ha_rows	kRowEstimateFallback = 1000
	A fallback cardinality estimate that is used in case the storage engine cannot provide one (like for table functions). More...

Function Documentation

AddCost()

void AddCost	(	THD *	thd,
		const ContainedSubquery &	subquery,
		double	num_rows,
		FilterCost *	cost
	)

Used internally by EstimateFilterCost() only.

EstimateAggregateCost()

void EstimateAggregateCost	(	AccessPath *	path,
		const Query_block *	query_block,
		std::string *	trace = nullptr
	)

Estimate costs and result row count for an aggregate operation.

Parameters

[in,out]	path	The AGGREGATE path.
[in]	query_block	The Query_block to which 'path' belongs.
[in,out]	trace	Optimizer trace text.

EstimateCostForRefAccess()

double EstimateCostForRefAccess	(	THD *	thd,
		TABLE *	table,
		unsigned	key_idx,
		double	num_output_rows
	)

EstimateDeleteRowsCost()

void EstimateDeleteRowsCost

(

AccessPath *

path

)

EstimateFilterCost() [1/2]

FilterCost EstimateFilterCost ( THD *  thd, double  num_rows, const Mem_root_array< ContainedSubquery > &  contained_subqueries  )

inline

A cheaper overload of EstimateFilterCost() that assumes that all contained subqueries have already been extracted (ie., it skips the walking, which can be fairly expensive).

This data is typically computed by FindContainedSubqueries().

EstimateFilterCost() [2/2]

FilterCost EstimateFilterCost	(	THD *	thd,
		double	num_rows,
		Item *	condition,
		const Query_block *	outer_query_block
	)

Estimate the cost of evaluating “condition”, “num_rows” times.

This is a fairly rudimentary estimation, but it includes the cost of any subqueries that may be present and that need evaluation.

EstimateLimitOffsetCost()

void EstimateLimitOffsetCost

(

AccessPath *

path

)

Estimate the costs and row count for a LIMIT_OFFSET AccessPath.

EstimateMaterializeCost()

void EstimateMaterializeCost	(	THD *	thd,
		AccessPath *	path
	)

EstimateSortCost()

void EstimateSortCost

(

AccessPath *

path

)

EstimateStreamCost()

void EstimateStreamCost

(

AccessPath *

path

)

Estimate the costs and row count for a STREAM AccessPath.

EstimateUpdateRowsCost()

void EstimateUpdateRowsCost

(

AccessPath *

path

)

FindOutputRowsForJoin()

double FindOutputRowsForJoin ( double  left_rows, double  right_rows, const JoinPredicate *  edge  )

inline

Variable Documentation

kAggregateOneRowCost

constexpr double kAggregateOneRowCost = 0.1

constexpr

kApplyOneFilterCost

constexpr double kApplyOneFilterCost = 0.1

constexpr

kHashBuildOneRowCost

constexpr double kHashBuildOneRowCost = 0.1

constexpr

kHashProbeOneRowCost

constexpr double kHashProbeOneRowCost = 0.1

constexpr

kHashReturnOneRowCost

constexpr double kHashReturnOneRowCost = 0.07

constexpr

kMaterializeOneRowCost

constexpr double kMaterializeOneRowCost = 0.1

constexpr

kMaxItemLengthEstimate

constexpr size_t kMaxItemLengthEstimate = 4096

constexpr

When we make cost estimates, we use this as the maximal length the values we get from evaluating an Item (in bytes).

Actual values of e.g. blobs may be much longer, but even so we use this as an upper limit when doing cost calculations. (For context,

See also

Item::max_length .)

kRowEstimateFallback

constexpr ha_rows kRowEstimateFallback = 1000

constexpr

A fallback cardinality estimate that is used in case the storage engine cannot provide one (like for table functions).

It's a fairly arbitrary non-zero value.

kSortOneRowCost

constexpr double kSortOneRowCost = 0.1

constexpr

kWindowOneRowCost

constexpr double kWindowOneRowCost = 0.1

constexpr