code: public void format() throws IOException {
      URI location = getLocation();
      LOG.info("Formatting {}", location);
      if (mUfs.isDirectory(location.toString())) {
        for (UfsStatus status : mUfs.listStatus(location.toString())) {
          String childPath = URIUtils.appendPathOrDie(location, status.getName()).toString();
          if (status.isDirectory()
              && !mUfs.deleteDirectory(childPath, DeleteOptions.defaults().setRecursive(true))
              || status.isFile() && !mUfs.deleteFile(childPath)) {
            throw new IOException(String.format("Failed to delete %s", childPath));
          }
        }
      } else if (!mUfs.mkdirs(location.toString())) {
        throw new IOException(String.format("Failed to create %s", location));
      }
  
      // Create a breadcrumb that indicates that the journal folder has been formatted.
      UnderFileSystemUtils.touch(mUfs, URIUtils.appendPathOrDie(location,
          ServerConfiguration.get(PropertyKey.MASTER_FORMAT_FILE_PREFIX) + System.currentTimeMillis())
          .toString());
    }
docs: Formats the journal.