protected boolean readObject(int pos) throws IOException {

    dataFile.seek((long) pos * cacheFileScale);

    int size = dataFile.readInt();

    rowIn.resetRow(pos, size);
    dataFile.read(rowIn.getBuffer(), 4, size - 4);

    return true;
  }
  protected synchronized RowInputInterface readObject(int pos) throws IOException {

    dataFile.seek((long) pos * cacheFileScale);

    int size = dataFile.readInt();

    rowIn.resetRow(pos, size);
    dataFile.read(rowIn.getBuffer(), 4, size - 4);

    return rowIn;
  }
  protected int readSize(int pos) throws IOException {

    dataFile.seek((long) pos * cacheFileScale);

    return dataFile.readInt();
  }
  /**
   * Opens the *.data file for this cache, setting the variables that allow access to the particular
   * database version of the *.data file.
   */
  public void open(boolean readonly) throws HsqlException {

    fileFreePosition = 0;

    try {
      boolean preexists = database.isFilesInJar();
      long freesize = 0;

      if (!preexists && fa.isStreamElement(fileName)) {
        if (database.isStoredFileAccess()) {
          preexists = true;
        } else {

          // discard "empty" databases
          File f = new File(fileName);

          preexists = f.length() > INITIAL_FREE_POS;
        }
      }

      if (preexists) {
        String version =
            database.getProperties().getProperty(HsqlDatabaseProperties.hsqldb_cache_version);
        boolean v17 = HsqlDatabaseProperties.VERSION_STRING_1_7_0.equals(version);

        // for later versions
        boolean v18 = HsqlDatabaseProperties.VERSION_STRING_1_8_0.equals(version);

        if (!v17) {
          throw Trace.error(Trace.WRONG_DATABASE_FILE_VERSION);
        }
      }

      boolean isNio = database.getProperties().isPropertyTrue("hsqldb.nio_data_file");
      int fileType = isNio ? ScaledRAFile.DATA_FILE_NIO : ScaledRAFile.DATA_FILE_RAF;

      if (database.isFilesInJar()) {
        fileType = ScaledRAFile.DATA_FILE_JAR;
      }

      // [email protected] - change to file access api
      String cname = database.getURLProperties().getProperty("storage_class_name");
      String skey = database.getURLProperties().getProperty("storage_key");

      dataFile = ScaledRAFile.newScaledRAFile(fileName, readonly, fileType, cname, skey);

      if (preexists) {
        dataFile.seek(FLAGS_POS);

        int flags = dataFile.readInt();

        hasRowInfo = BitMap.isSet(flags, FLAG_ROWINFO);

        dataFile.seek(LONG_EMPTY_SIZE);

        freesize = dataFile.readLong();

        dataFile.seek(LONG_FREE_POS_POS);

        fileFreePosition = dataFile.readLong();

        if (fileFreePosition < INITIAL_FREE_POS) {
          fileFreePosition = INITIAL_FREE_POS;
        }
      } else {
        fileFreePosition = INITIAL_FREE_POS;
      }

      resetBuffers();

      fileModified = false;
      freeBlocks = new DataFileBlockManager(FREE_BLOCKS_COUNT, cacheFileScale, freesize);
    } catch (Exception e) {
      database.logger.appLog.logContext(e);
      close(false);

      throw Trace.error(Trace.FILE_IO_ERROR, Trace.DataFileCache_open, new Object[] {e, fileName});
    }
  }