@Override
  protected void closeOp(boolean abort) throws HiveException {
    if (LOG.isInfoEnabled()) {
      for (int i = 0; i < numParents; i++) {
        LOG.info(id + ", tag=" + i + ", forwarded " + cntrs[i] + " rows");
      }
    }
  }
Calls initialize on each of the children with outputObjetInspector as the
output row format.
ql/src/java/org/apache/hadoop/hive/ql/exec/MuxOperator.java