code: private synchronized void refreshCachedData() throws IOException {
      IOUtils.closeStream(committedTxnId);
      
      File currentDir = journalStorage.getSingularStorageDir().getCurrentDir();
      this.lastPromisedEpoch = new PersistentLongFile(
          new File(currentDir, LAST_PROMISED_FILENAME), 0);
      this.lastWriterEpoch = new PersistentLongFile(
          new File(currentDir, LAST_WRITER_EPOCH), 0);
      this.committedTxnId = new BestEffortLongFile(
          new File(currentDir, COMMITTED_TXID_FILENAME),
          HdfsConstants.INVALID_TXID);
      metrics.lastWriterEpoch.set(lastWriterEpoch.get());
    }
docs: Reload any data that may have been cached. This is necessary
  when we first load the Journal, but also after any formatting
  operation, since the cached data is no longer relevant.
  @throws IOException