Unsupervised Domain Ranking in Large-Scale Web Crawls

With the proliferation of web spam and infinite autogenerated web content, large-scale web crawlers require low-complexity ranking methods to effectively budget their limited resources and allocate bandwidth to reputable sites. In this work, we assume crawls that produce frontiers orders of magnitude larger than RAM, where sorting of pending URLs is infeasible in real time. Under these constraints, the main objective is to quickly compute domain budgets and decide which of them can be massively crawled. Those ranked at the top of the list receive aggressive crawling allowances, while all other domains are visited at some small default rate. To shed light on Internet-wide spam avoidance, we study topology-based ranking algorithms on domain-level graphs from the two largest academic crawls: a 6.3B-page IRLbot dataset and a 1B-page ClueWeb09 exploration. We first propose a new methodology for comparing the various rankings and then show that in-degree BFS-based techniques decisively outperform classic PageRank-style methods, including TrustRank. However, since BFS requires several orders of magnitude higher overhead and is generally infeasible for real-time use, we propose a fast, accurate, and scalable estimation method called TSE that can achieve much better crawl prioritization in practice. It is especially beneficial in applications with limited hardware resources.