Nerval's Lobster writes "Facebook's Graph Search, its new and powerful way of searching the social network for all manner of information, has drawn a lot of attention since its January unveiling. Some have praised its innovation; others have wondered openly whether its search abilities will end up threatening Google and LinkedIn. Still more have questioned what it all means for users' privacy—always a touchy subject in conjunction with Facebook. The social network previously revealed how it's adjusting its hardware infrastructure to deal with the spike in traffic that will come from interactions with Graph Search (short answer: the Disaggregated Rack, which will break up hardware resources and scale them independently of one another). Now, in a new blog posting, it's offering a bit more with regard to the software side of things, and how the company repurposed an existing system to solve Graph Search's enormous engineering challenge. Bottom line: Facebook's engineers and executives finally decided on Unicorn, an inverted-index system they'd had in development for quite some time."