indexUpdater.setPriority(indexUpdaterPriority);
        indexUpdater.setSessionIdList(sessionIdList);
        indexUpdater.setDaemon(true);
        indexUpdater.setCrawlerList(crawlerList);
        getAvailableBoostDocumentRuleList().forEach(rule -> {
            indexUpdater.addDocBoostMatcher(new org.codelibs.fess.indexer.DocBoostMatcher(rule));
        });
        indexUpdater.start();

        int startedCrawlerNum = 0;