Cassandra was released in 2008. Facebook hit 1 billion users ~ 2012, and 2 billion ~ 2017. Back when Cassandra was released, they had a 'mere' 100 million users.
Facebook stats:
https://www.statista.com/statistics/264810/number-of-monthly...
Facebook stats:
https://www.statista.com/statistics/264810/number-of-monthly...