code: public static String[] fastSplitKey(String key) {
      int i = key.indexOf(':');
      if(-1 == i) {
        return new String[]{key};
      }
      else {
        int j = key.indexOf(':', i+1);
        if (-1 != j) {
          return null;
        }
        else {
          return new String[]{key.substring(0, i), key.substring(i+1)};
        }
      }
    }
docs: Java's string split is very expensive due to regexes.
  Implement our own simple version instead.