Up front: I'm thinking about leaving NoSQL because I hate its memory model. SQL requires joins to get a "document" back. In order to properly optimize that pro

Up front: I'm thinking about leaving NoSQL because I hate its memory model. SQL requires joins to get a "document" back. In order to properly optimize that process, you'll want an index. Most DBs don't do that (if I understand them correctly). See 1 for details about PG. NoSQLs like Mongo lack joins. As a result you pack most of your joinable data into a document. When you need some manner of linked relation, you can store either the key to the collection, or a URI that goes through your API to that collection. In either case, you're pegging against an indexed key (probably the PK). http://dba.stackexchange.com/questions/53809/need-for-indexes-on-foreign-keys http://dba.stackexchange.com/questions/53809/need-for-indexe...