public boolean rewritePost()

in algebricks/algebricks-rewriter/src/main/java/org/apache/hyracks/algebricks/rewriter/rules/subplan/MoveFreeVariableOperatorOutOfSubplanRule.java [72:182]
84 lines of code
20 McCabe index (conditional complexity)

    public boolean rewritePost(Mutable<ILogicalOperator> opRef, IOptimizationContext context)
            throws AlgebricksException {
        AbstractLogicalOperator op0 = (AbstractLogicalOperator) opRef.getValue();
        if (op0.getOperatorTag() != LogicalOperatorTag.SUBPLAN) {
            return false;
        }
        SubplanOperator subplan = (SubplanOperator) op0;

        Mutable<ILogicalOperator> leftRef = subplan.getInputs().get(0);
        if (((AbstractLogicalOperator) leftRef.getValue()).getOperatorTag() == LogicalOperatorTag.EMPTYTUPLESOURCE) {
            return false;
        }

        ListIterator<ILogicalPlan> plansIter = subplan.getNestedPlans().listIterator();
        ILogicalPlan p = null;
        while (plansIter.hasNext()) {
            p = plansIter.next();
        }
        if (p == null) {
            return false;
        }
        if (p.getRoots().size() != 1) {
            return false;
        }
        Mutable<ILogicalOperator> opRef1 = p.getRoots().get(0);

        //The root operator will not be movable. Start with the second op
        AbstractLogicalOperator op1 = (AbstractLogicalOperator) opRef1.getValue();
        if (op1.getInputs().size() != 1) {
            return false;
        }
        Mutable<ILogicalOperator> op2Ref = op1.getInputs().get(0);

        //Get all variables that come from outside of the loop
        Set<LogicalVariable> free = new HashSet<LogicalVariable>();
        OperatorPropertiesUtil.getFreeVariablesInSelfOrDesc(op1, free);

        while (op2Ref != null) {
            //Get the operator that we want to look at
            AbstractLogicalOperator op2 = (AbstractLogicalOperator) op2Ref.getValue();

            //Make sure we are looking at subplan with a scan/join
            if (op2.getInputs().size() != 1 || !descOrSelfIsScanOrJoin(op2)) {
                return false;
            }
            boolean notApplicable = false;

            //Get its used variables
            Set<LogicalVariable> used = new HashSet<LogicalVariable>();

            //not movable if the operator is not an assign or subplan
            //Might be helpful in the future for other operations in the future
            if (movableOperator(op2.getOperatorTag())) {
                if (op2.getOperatorTag() == LogicalOperatorTag.ASSIGN) {
                    VariableUtilities.getUsedVariables(op2, used);
                } else if (op2.getOperatorTag() == LogicalOperatorTag.SUBPLAN) {
                    // Nested plan must have an aggregate root.
                    ListIterator<ILogicalPlan> subplansIter = ((SubplanOperator) op2).getNestedPlans().listIterator();
                    ILogicalPlan plan = null;
                    while (subplansIter.hasNext()) {
                        plan = subplansIter.next();
                    }
                    if (plan == null) {
                        return false;
                    }
                    if (plan.getRoots().size() != 1) {
                        return false;
                    }
                    ILogicalOperator op3 = plan.getRoots().get(0).getValue();
                    if (op3.getOperatorTag() != LogicalOperatorTag.AGGREGATE) {
                        return false;
                    }
                    // Used variables do not include ones created in the subplan.
                    VariableUtilities.getUsedVariables(op2, used);
                    Set<LogicalVariable> subplanProducedAndDown = new HashSet<LogicalVariable>();
                    VariableUtilities.getProducedVariablesInDescendantsAndSelf(op3, subplanProducedAndDown);
                    used.removeAll(subplanProducedAndDown);
                } else {
                    notApplicable = true;
                }
            } else {
                notApplicable = true;
            }

            //Make sure that all of its used variables come from outside
            for (LogicalVariable var : used) {
                if (!free.contains(var)) {
                    notApplicable = true;
                }
            }

            if (notApplicable) {
                op2Ref = op2.getInputs().get(0);
            } else {
                //Make the input of op2 be the input of op1
                op2Ref.setValue(op2.getInputs().get(0).getValue());

                //Make the outside of the subplan the input of op2
                Mutable<ILogicalOperator> outsideRef = op2.getInputs().get(0);
                outsideRef.setValue(op0.getInputs().get(0).getValue());

                //Make op2 the input of the subplan
                Mutable<ILogicalOperator> op2OutsideRef = op0.getInputs().get(0);
                op2OutsideRef.setValue(op2);

                return true;
            }

        }
        return false;
    }