anonymous_namespace{cost_model.cc}::AggregateRowEstimator Class Reference

This class finds disjoint sets of aggregation terms that form prefixes of some non-hash index, and makes row estimates for those sets based on index metadata. More...

Classes
struct	Prefix
	A prefix of some key where each key_part corresponds to an aggregation term. More...

Public Member Functions
	AggregateRowEstimator (THD *thd, TermArray terms)
	AggregateRowEstimator (const AggregateRowEstimator &)=delete
AggregateRowEstimator &	operator= (const AggregateRowEstimator &)=delete
double	MakeNextEstimate (THD *thd)
	Get the next row estimate. More...
const MutableOverflowBitset &	GetConsumedTerms () const
	Get the set of terms for which we have found an index. More...

Static Public Attributes
static constexpr double	kNoEstimate = -1.0
	Used to indicate that no more suitable indexes could be found. More...

Private Member Functions
TermArray::const_iterator	FindField (const Field *field) const
	Find an Item_field pointing to 'field' in 'm_terms', if there is one. More...

Private Attributes
TermArray	m_terms
	The aggregation terms. More...
MutableOverflowBitset	m_consumed_terms
	The set of terms mapped to an index so far. More...
Mem_root_array< Prefix * >	m_prefixes
	The index prefixes we found for 'm_terms'. More...

Detailed Description

This class finds disjoint sets of aggregation terms that form prefixes of some non-hash index, and makes row estimates for those sets based on index metadata.

Constructor & Destructor Documentation

AggregateRowEstimator() [1/2]

anonymous_namespace{cost_model.cc}::AggregateRowEstimator::AggregateRowEstimator	(	THD *	thd,
		TermArray	terms
	)

Parameters

thd	Current thread.
terms	The aggregation terms.

AggregateRowEstimator() [2/2]

anonymous_namespace{cost_model.cc}::AggregateRowEstimator::AggregateRowEstimator ( const AggregateRowEstimator &  )

delete

Member Function Documentation

FindField()

TermArray::const_iterator anonymous_namespace{cost_model.cc}::AggregateRowEstimator::FindField ( const Field *  field ) const

inlineprivate

Find an Item_field pointing to 'field' in 'm_terms', if there is one.

Parameters

field

The field we look for.

Returns

An iterator to the position of 'field' in m_terms, or m_terms.cend().

GetConsumedTerms()

const MutableOverflowBitset & anonymous_namespace{cost_model.cc}::AggregateRowEstimator::GetConsumedTerms ( ) const

inline

Get the set of terms for which we have found an index.

Bit number corresponds to position in the 'terms' argument to the constructor.

MakeNextEstimate()

double anonymous_namespace{cost_model.cc}::AggregateRowEstimator::MakeNextEstimate

(

THD *

thd

)

Get the next row estimate.

We make the estimate as follows:

1. Find the (non-hash) index where the remaining aggregation terms form the longest prefix of the index fields. For example, if we have aggregation terms [a,b,c,d] and we have indexes ix1 on [a,b], ix2 on [d,c,b,e], we pick ix2.
2. Make an estimate of the number of distinct values for those fields (i.e. [d,c,b]) using index statistics. This is the row estimate.
3. Remove those fields from the set of remaining terms. (In the example above, only [a] would now remain.
4. Return the row estimate to the caller.

Returns

The estimate, or kNoEstimate if no more suitable indexes could be found.

operator=()

AggregateRowEstimator & anonymous_namespace{cost_model.cc}::AggregateRowEstimator::operator= ( const AggregateRowEstimator &  )

delete

Member Data Documentation

kNoEstimate

constexpr double anonymous_namespace{cost_model.cc}::AggregateRowEstimator::kNoEstimate = -1.0

staticconstexpr

Used to indicate that no more suitable indexes could be found.

m_consumed_terms

MutableOverflowBitset anonymous_namespace{cost_model.cc}::AggregateRowEstimator::m_consumed_terms

private

The set of terms mapped to an index so far.

m_prefixes

Mem_root_array<Prefix *> anonymous_namespace{cost_model.cc}::AggregateRowEstimator::m_prefixes

private

The index prefixes we found for 'm_terms'.

m_terms

TermArray anonymous_namespace{cost_model.cc}::AggregateRowEstimator::m_terms

private

The aggregation terms.

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

• sql/join_optimizer/cost_model.cc