@Override
  public MapJoinRowContainer copy() {
    MapJoinEagerRowContainer result = new MapJoinEagerRowContainer();
    for(List<Object> item : list) {
      result.addRow(item);
    }
    return result;
  }
Remove all elements in the RowContainer.
ql/src/java/org/apache/hadoop/hive/ql/exec/persistence/MapJoinEagerRowContainer.java