cost

Documentation

Index

• Constants
• Variables

Constants

const (
	// SelectionFactor is the default factor of the selectivity.
	// For example, If we have no idea how to estimate the selectivity
	// of a Selection or a JoinCondition, we can use this default value.
	SelectionFactor = 0.8

	DistinctFactor = 0.8
)

******************************* Factors *******************************

const (
	// SmallScanThreshold means: If the actual row count is much more
	// than the limit count, the unordered scan may cost much more than keep order.
	// So when a limit exists, we don't apply the DescScanFactor.
	SmallScanThreshold = 10000
)

// ******************************* Thresholds *******************************

Variables

var AggFuncFactor = map[string]float64{
	ast.AggFuncCount:       1.0,
	ast.AggFuncSum:         1.0,
	ast.AggFuncAvg:         2.0,
	ast.AggFuncFirstRow:    0.1,
	ast.AggFuncMax:         1.0,
	ast.AggFuncMin:         1.0,
	ast.AggFuncGroupConcat: 1.0,
	ast.AggFuncBitOr:       0.9,
	ast.AggFuncBitXor:      0.9,
	ast.AggFuncBitAnd:      0.9,
	ast.AggFuncVarPop:      3.0,
	ast.AggFuncVarSamp:     3.0,
	ast.AggFuncStddevPop:   3.0,
	ast.AggFuncStddevSamp:  3.0,
	"default":              1.5,
}

AggFuncFactor is the basic factor for aggregation.