How to crawl a quarter billion webpages in 40 hours
In my experience, one of the hardest parts of writing a web crawler is URL selection:<p>After crawling your list of seed URLs, where do you go next? How do you make sure you don't crawl the same content multiple times because it has a slightly different URL? How to avoid getting stuck on unimportant spam sites with autogenerated content?<p>Because the author only crawled domains from a limited set and only for a short time, he did not need to care about that part. Nonetheless, it's a great article that shows many of the pitfalls of writing a webcrawler.