public void replaceParent(Operator<? extends OperatorDesc> parent,
      Operator<? extends OperatorDesc> newParent) {
    int parentIndex = parentOperators.indexOf(parent);
    assert parentIndex != -1;
    parentOperators.set(parentIndex, newParent);
  }
Replace one parent with another at the same position. Chilren of the new
parent are not updated

@param parent
         the old parent
@param newParent
         the new parent
ql/src/java/org/apache/hadoop/hive/ql/exec/Operator.java