Google's simhash paper shows how to do 8 billion 64bit fingerprints in memory: Detecting Near-Duplicates for Web Crawling (http://www.wwwconference.org/www2007

Google's simhash paper shows how to do 8 billion 64bit fingerprints in memory: Detecting Near-Duplicates for Web Crawling (http://www.wwwconference.org/www2007/papers/paper215.pdf http://www.wwwconference.org/www2007/papers/paper215.pdf) SEOMoz has in-memory and db-backed implementations of simhash in Python (https://github.com/seomoz?query=simhash https://github.com/seomoz?query=simhash)