computing is so cheap that most people can delegate to a database. at some point tho, if money is a problem and you don't have the computing resources, you can squeeze more out of that hardware by using more specialized DBs, (graph, doc, column), something like redis, etc, but then at some point those might not map very nice to your problem and in which case custom data structures will get you far. Hence the reason FAANGs are big on algorithm & DS questions during interviews.