Yeah, it isn't something that is feasible if you can't tailor the infrastructure to the underlying data. An SQL backend is about as generic as it gets, hence the poor results. Enterprise DB deployments get away with it because they can justify throwing a lot more hardware behind a centralized generic data store.

Give that second link a closer look if you change your mind. It demonstrates a way of indexing 1.6 billion 80B strings in 24GB, and then returning the result of a fixed string search in 100ms. That is the reward you get when you venturing outside of the LAMP stack: less resource consumption, greater performance, increased utility.