oh... dude... exact same mistake twice... OK, let me try to be more constructive. Since accounts are independent, shard based on account (in the application, n

oh... dude... exact same mistake twice... OK, let me try to be more constructive. Since accounts are independent, shard based on account (in the application, not in some magic shard-distributing layer). Treat each shard as its own cluster. If you want super fast requests but can accept being down for an hour or two a couple times a year, a shard can be a single beefy host with a replicating slave. I'd consider either Redis or Mysql/Postgresql. Really, these old-style sql databases can be the fastest things that have the kind of consistency you need. I've maintained a mongodb cluster configured a couple of different ways. Performance at high load and reasonable consistency is not as great as some older alternatives.