code: public List<Long> getAllVersions() throws IOException {
          List<Long> ret = new ArrayList<>();
          for (String s : listDir(_root)) {
              if (s.endsWith(FINISHED_VERSION_SUFFIX)) {
                  ret.add(validateAndGetVersion(s));
              }
          }
          Collections.sort(ret);
          Collections.reverse(ret);
          return ret;
      }
docs: Sorted from most recent to oldest