public boolean hasNext() {
    return readBufferUsed || rowsOnDisk > 0;
  }
An eager object container that puts every row directly to output stream.
The object can be of any type.
Kryo is used for the serialization/deserialization.
When reading, we load IN_MEMORY_NUM_ROWS rows from input stream to memory batch by batch.
ql/src/java/org/apache/hadoop/hive/ql/exec/persistence/ObjectContainer.java