I always see this discussion cast as one between scalability (KV) and dev efficiency (SQL), but other reasons to adopt columnar databases include: 1. Difficult

I always see this discussion cast as one between scalability (KV) and dev efficiency (SQL), but other reasons to adopt columnar databases include: 1. Difficulty in transitioning a system with SQL-Gone-Wild to a system that can be implemented with other dbs without complexity overdrive 2. Escalating costs to get any additional availability guarantees out of SQL (availability & cost are key business issues) In AWS & Google Cloud, you're going to need to pay outright for capacity as well as capacity devoted db recovery (a replica / set of replicas in another availability zone). On the other side with something like dynamo / cloud datastore, your payment model is based on requests / sec and the costs for replicated data. I'm just saying that there's nothing simple to deciding where price / availability / dev productivity balances will lead you to, and you can be an inexperienced developer who chooses either side of these technologies without really understanding the full story.