public boolean pushRow() throws IOException, HiveException {
    if (operator == null) {
      return false;
    }

    if (work.getRowsComputedUsingStats() != null) {
      for (List<Object> row : work.getRowsComputedUsingStats()) {
        operator.process(row, 0);
      }
      flushRow();
      return true;
    }
    InspectableObject row = getNextRow();
    if (row != null) {
      pushRow(row);
    } else {
      flushRow();
    }
    return row != null;
  }
Get the next row and push down it to operator tree.
Currently only used by FetchTask.
ql/src/java/org/apache/hadoop/hive/ql/exec/FetchOperator.java