[the_paul]

...a competently engineered Turing Machine can do everything NoSQL databases can, particularly limited databases like MongoDB. ... Emacs is just as fast as NoSQL du jour in the hands of someone that knows it.

FTFY.

The difference between using a good competently engineered distributed database and PostgreSQL is that when your prime concerns are horizontal scaling and operations costs, the distributed database can be an order of magnitude simpler and faster than PostgreSQL given the same amount of effort.