How Google Code Search Worked: Regex Matching with a Trigram Index (2012)
Very cool! - Most search problems are solved this way -  interesting index data modeling to the needed use cases, not magic machine learning neural network unicorns. Many want to sell you the latter. The thing that gets the job done is usually the former.One big reasons for this is the need for really good training data to do supervised learning on search problems. If you’re Google or Wikipedia, you can get this data. But many struggle to understand what a good result was for a query based on clicks and other user data due to low volumes of traffic.