org.eigenbase.relopt
Interface RelOptCost

All Known Implementing Classes:

MockRelOptCost, RelOptCostImpl, VolcanoCost

public interface RelOptCost

RelOptCost defines an interface for optimizer cost in terms of number of rows processed, CPU cost, and I/O cost. Optimizer implementations may use all of this information, or selectively ignore portions of it. The specific units for all of these quantities are rather vague; most relational expressions provide a default cost calculation, but optimizers can override this by plugging in their own cost models with well-defined meanings for each unit. Optimizers which supply their own cost models may also extend this interface with additional cost metrics such as memory usage.

Method Summary

double	divideBy(RelOptCost cost) Computes the ratio between this cost and another cost.
boolean	equals(RelOptCost cost) Compares this to another cost.
double	getCpu()
double	getIo()
double	getRows()
boolean	isEqWithEpsilon(RelOptCost cost) Compares this to another cost, allowing for slight roundoff errors.
boolean	isInfinite()
boolean	isLe(RelOptCost cost) Compares this to another cost.
boolean	isLt(RelOptCost cost) Compares this to another cost.
RelOptCost	minus(RelOptCost cost) Subtracts another cost from this.
RelOptCost	multiplyBy(double factor) Multiplies this cost by a scalar factor.
RelOptCost	plus(RelOptCost cost) Adds another cost to this.
String	toString() Forces implementations to override Object.toString() and provide a good cost rendering to use during tracing.

Method Detail

getRows

double getRows()

Returns:

number of rows processed; this should not be confused with the row count produced by a relational expression (RelNode.getRows())

getCpu

double getCpu()

Returns:

usage of CPU resources

getIo

double getIo()

Returns:

usage of I/O resources

isInfinite

boolean isInfinite()

Returns:

true iff this cost represents an expression that hasn't actually been implemented (e.g. a pure relational algebra expression) or can't actually be implemented, e.g. a transfer of data between two disconnected sites

equals

boolean equals(RelOptCost cost)

Compares this to another cost.

Parameters:

cost - another cost

Returns:

true iff this is exactly equal to other cost

isEqWithEpsilon

boolean isEqWithEpsilon(RelOptCost cost)

Compares this to another cost, allowing for slight roundoff errors.

Parameters:

cost - another cost

Returns:

true iff this is the same as the other cost within a roundoff margin of error

isLe

boolean isLe(RelOptCost cost)

Compares this to another cost.

Parameters:

cost - another cost

Returns:

true iff this is less than or equal to other cost

isLt

boolean isLt(RelOptCost cost)

Compares this to another cost.

Parameters:

cost - another cost

Returns:

true iff this is strictly less than other cost

plus

RelOptCost plus(RelOptCost cost)

Adds another cost to this.

Parameters:

cost - another cost

Returns:

sum of this and other cost

minus

RelOptCost minus(RelOptCost cost)

Subtracts another cost from this.

Parameters:

cost - another cost

Returns:

difference between this and other cost

multiplyBy

RelOptCost multiplyBy(double factor)

Multiplies this cost by a scalar factor.

Parameters:

factor - scalar factor

Returns:

scalar product of this and factor

divideBy

double divideBy(RelOptCost cost)

Computes the ratio between this cost and another cost.

divideBy is the inverse of multiplyBy(double). For any finite, non-zero cost and factor f, cost.divideBy(cost.multiplyBy(f)) yields 1 / f.

Parameters:

cost - Other cost

Returns:

Ratio between costs

toString

String toString()

Forces implementations to override Object.toString() and provide a good cost rendering to use during tracing.

Overrides:

toString in class Object