[Volundr]

Disclaimer: I have a lot more experience with postgres than mongo. I have worked with multi billion row databases in postgres. I have not on mongo.

> When data size goes to a billion rows, Postgres is tough. MongoDB just works without issue.

Joins are tough at a billion rows in Postgres. PK lookups and simple index queries of the type mongo is good at Postgres is generally good at too. The main thing mongo has over postgres is ease of sharding if one is looking to scale horizontally.