* @return the number of documents that were deleted
     */
    protected long deleteByQueryBuilder(final SearchEngineClient searchEngineClient, final String index, final QueryBuilder queryBuilder) {
        refreshIndex(searchEngineClient, index);
        final long numOfDeleted = searchEngineClient.deleteByQuery(index, queryBuilder);
        if (logger.isDebugEnabled()) {
            logger.debug("Deleted {} stale documents.", numOfDeleted);