public void update(LinkRelevance linkRelevance) {
        String url = linkRelevance.getURL().toString();
        LinkRelevance link = urlRelevance.get(url);
        if (link != null) {
            if (link.getRelevance() > 0) { // not visited url
                urlRelevance.put(url, linkRelevance);
            }
        }
    }
DEPRECATED: may cause OutOfMemoryError on large crawls. TODO: Provide an method that uses an
iterator, and/or load just a sample of the data.
ache/src/main/java/achecrawler/link/frontier/Frontier.java