Class CalcRelSplitter


public abstract class CalcRelSplitter extends Object
CalcRelSplitter operates on a Calc with multiple RexCall sub-expressions that cannot all be implemented by a single concrete RelNode.

For example, the Java and Fennel calculator do not implement an identical set of operators. The Calc can be used to split a single Calc with mixed Java- and Fennel-only operators into a tree of Calc object that can each be individually implemented by either Java or Fennel.and splits it into several Calc instances.

Currently the splitter is only capable of handling two "rel types". That is, it can deal with Java vs. Fennel Calcs, but not Java vs. Fennel vs. some other type of Calc.

See ProjectToWindowRule for an example of how this class is used.

  • Field Details

  • Method Details

    • handle

      protected RelNode handle(RelNode rel)
      Opportunity to further refine the relational expression created for a given level. The default implementation returns the relational expression unchanged.
    • canImplement

      protected boolean canImplement(LogicalCalc rel, String relTypeName)
      Returns whether a relational expression can be implemented solely in a given CalcRelSplitter.RelType.
      rel - Calculation relational expression
      relTypeName - Name of a CalcRelSplitter.RelType
      Whether relational expression can be implemented
    • getCohorts

      protected List<Set<Integer>> getCohorts()
      Returns a list of sets of expressions that should be on the same level.

      For example, if this method returns { {3, 5}, {4, 7} }, it means that expressions 3 and 5, should be on the same level, and expressions 4 and 7 should be on the same level. The two cohorts do not need to be on the same level.

      The list is best effort. If it is not possible to arrange that the expressions in a cohort are on the same level, the execute() method will still succeed.

      The default implementation of this method returns the empty list; expressions will be put on the most suitable level. This is generally the lowest possible level, except for literals, which are placed at the level where they are used.

      List of cohorts, that is sets of expressions, that the splitting algorithm should attempt to place on the same level