I did it in sqlite. Putting json in SQL table is trivial. Putting additional table for kv search idx is also trivial and extremely fast. Best of all, it works in android iOS and python with one simple wrapper class wrapper layer (<100 line of code) I was able to implement an user authentication web server + db code in 300 line of python with and kind user attributes that can be added later on. I read somewhere that fb use mysql as pure kv data store.