*
   * @since 22.0
   */
  public long approximateElementCount() {
    long bitSize = bits.bitSize();
    long bitCount = bits.bitCount();

    /*
     * Each insertion is expected to reduce the # of clear bits by a factor of
     * `numHashFunctions/bitSize`. So, after n insertions, expected bitCount is `bitSize * (1 - (1 -

                            .replace("\"_index\":\"fess_log.", "\"_index\":\"" + fessConfig.getIndexLogIndex() + "."))
                    .reduce((prev, line) -> {
                        try {
                            if (StringUtil.isBlank(prev)) {
                                final Map<String, Map<String, String>> result =