This post is a great 101, but it doesn't provide much info on what kind of setup you run at Mixpanel. I see you ditched Cassandra, though, and you mention Riak.

This post is a great 101, but it doesn't provide much info on what kind of setup you run at Mixpanel. I see you ditched Cassandra, though, and you mention Riak. Are you using Riak, rolling your own sharding layer, or what?