I was ask a common design question, which I have never really studied. The question was asked vaguely because the interviewers expected me to have come across the question. I am confident that I addressed common concerns like scaling, database optimization, caching and distribution. Even though I applied the right scaling mechanism, one of the interviewers was rather disappointed that I didn't the term for the concept I used. It's disappointing that it's more about show off for the interwers than actually assessing one's knowledge and problem solving skills.