Interface RelOptCost

All Known Implementing Classes:
RelOptCostImpl

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 Details

    • getRows

      double getRows()
      Returns the number of rows processed; this should not be confused with the row count produced by a relational expression (RelNode.estimateRowCount(org.apache.calcite.rel.metadata.RelMetadataQuery)).
    • getCpu

      double getCpu()
      Returns usage of CPU resources.
    • getIo

      double getIo()
      Returns usage of I/O resources.
    • isInfinite

      boolean isInfinite()
      Returns whether 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