code: private PersistedRecoveryPaxosData getPersistedPaxosData(long segmentTxId)
        throws IOException {
      File f = journalStorage.getPaxosFile(segmentTxId);
      if (!f.exists()) {
        // Default instance has no fields filled in (they're optional)
        return null;
      }
      
      InputStream in = new FileInputStream(f);
      try {
        PersistedRecoveryPaxosData ret = PersistedRecoveryPaxosData.parseDelimitedFrom(in);
        Preconditions.checkState(ret != null &&
            ret.getSegmentState().getStartTxId() == segmentTxId,
            "Bad persisted data for segment %s: %s",
            segmentTxId, ret);
        return ret;
      } finally {
        IOUtils.closeStream(in);
      }
    }
docs: Retrieve the persisted data for recovering the given segment from disk.