code: private void removeDeletable()
     {
        String fileName = "deletable";
        try
        {
           if (indexDir.fileExists(fileName))
           {
              indexDir.deleteFile(fileName);
           }
        }
        catch (IOException e)
        {
           LOG.warn("Unable to remove file 'deletable'.", e);
        }
     }
docs: Removes the deletable file if it exists. The file is not used anymore in
  Jackrabbit versions >= 1.5.