[fortran77]

That was my first thought, too. You need these tricks to make MongoDB "WebScale"

http://www.mongodb-is-web-scale.com/

(I can get better results for Key-Value storage by using an SQL Database--Postgres or MariaDB--for key/values over MongoDB. And if you know SQL well, you can get even better results using a real relational database and optimal queries than pulling out keys/values and ad-hocking your relations in some Javascript code or whatever these web kids are doing.)

[jd_mongodb]

You don't pick a database like MongoDB purely for its key/value query performance. SQL will do really well until it does really badly, for example in cases where you exceed the limitations of the box/VM it is running on.