What if the web server itself acts as a mutable database? (Not ephemeral like Heroku.)
What if data is pre-queried inside memory to rely on backend-language filtering?
What if multiple files of NoSQL are used (like NeDB, because there is no real JOIN anyway)? What if NoSQL is already composed of multiple files (like LevelDB)? Also, what impacts the performance of JOINs?
What about array indexing, not to mention I don't know much about virtual table?