Works fine until user_id is null for whatever reason, or you hit the length limit on your cache key and start losing the end of it, or until your cache server d

Works fine until user_id is null for whatever reason, or you hit the length limit on your cache key and start losing the end of it, or until your cache server decides to just start serving up the same content for every key, because y’know, software (had this happen with memcached a long time back due to a tcp timing bug and a corrupted packet) and then you’re in the soup.