public void passExecContext(ExecMapperContext execContext) {
    this.setExecContext(execContext);
    for (Operator<? extends OperatorDesc> childOp : childOperators) {
      childOp.passExecContext(execContext);
    }
  }
Pass the execContext reference to every child operator
ql/src/java/org/apache/hadoop/hive/ql/exec/Operator.java