I have to disagree with you here. Elasticsearch has a "more like this" feature built into it, which would give you pretty much the desired functionality you're describing that Facebook and LinkedIn have. It's a free and open source technology that I've installed and maintained on my servers. All you have to do is feed it some JSON, which you can modify as you choose to bias it to your exact specifications. Google and AWS offer cloud search and database features which already have this type of functionality implemented for you - all you have to do is wire it to your app. I'm not saying that these problems were trivial to solve in the first place, but THEY HAVE ALREADY BEEN SOLVED BY GOOGLE AND AMAZON AND FACEBOOK AND A MILLION OTHER COMPANIES' ENGINEERS, and made available to you in a nice and easy to use package with a bow on top.

See here: https://cloud.google.com/products/bigquery/ https://cloud.google.com/products/cloud-datastore/ http://aws.amazon.com/cloudsearch/