"We quickly discounted this as it didn’t fit with our three pillars of Run Less Software and decided to consolidate on MySQL, specifically on AWS MySQL. As we were able to benefit from the pace of AWS innovation (and adopt AWS Aurora when it came along) we got 5x throughput at a 30% cost reduction."

It's worth noting that Aurora is compatible with PostgreSQL (as of Oct 2017) [1].

1. https://aws.amazon.com/blogs/aws/now-available-amazon-aurora...