@Override
  public Object put(Integer key, Object value) {
    Object result = super.put(key, value);
    //Every new element is added to FIFO too.
    if (result == null) {
      queue.add(key);
    }
    //If FIFO size reaches maxSize we evict the eldest entry.
    if (queue.size() > maxSize) {
      evictOne();
    }
    return result;
  }
True if the last range(s) of the partition are loaded into the cache.
@return
ql/src/java/org/apache/hadoop/hive/ql/exec/BoundaryCache.java