SortBuilders.fieldSort(OpenSearchUrlQueue.WEIGHT).order(SortOrder.DESC),
                SortBuilders.fieldSort(CREATE_TIME).order(SortOrder.ASC));
    }

    /**
     * Saves the session state (currently not implemented).
     *
     * @param sessionId The session ID.
     */
    @Override
    public void saveSession(final String sessionId) {
        // TODO use cache
    }