@Override
  public void append(ExtendedCell cell) throws IOException {
    if (historicalFilePath == null) {
      // The dual writing is not enabled and all cells are written to one file. We use
      // the live version file in this case
      liveFileWriter.append(cell);
      return;
    }
    appendCell(cell);
  }
@param dir Directory to create file in.
@return random filename inside passed <code>dir</code>
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/StoreFileWriter.java