We love PostgreSQL at Braintree. Although we use many different data stores (such as Riak, MongoDB, Redis, and Memcached), most of our core data is stored in PostgreSQL. It’s not as sexy as the new NoSQL databases, but PostgreSQL is consistent and incredibly reliable, two properties we value when storing payment information.
Related Articles:
https://www.braintreepayments.com/blog/scaling-postgresql-at-braintree-four-years-of-evolution/