public void read(MapJoinObjectSerDeContext context, ObjectInputStream in, Writable container)
  throws IOException, SerDeException {
    long numRows = in.readLong();
    for (long rowIndex = 0L; rowIndex < numRows; rowIndex++) {
      container.readFields(in);
      read(context, container);
    }
  }
Remove all elements in the RowContainer.
ql/src/java/org/apache/hadoop/hive/ql/exec/persistence/MapJoinEagerRowContainer.java