@Override
  public int hashCode() {
    return super.hashCode();
  }
Override by just returning the length for saving cost of method dispatching. If not, it will
call {@link ExtendedCell#getSerializedSize()} firstly, then forward to
{@link SizeCachedKeyValue#getSerializedSize(boolean)}. (See HBASE-21657)
hbase-common/src/main/java/org/apache/hadoop/hbase/SizeCachedByteBufferKeyValue.java