I can scale PostgresSQL pretty well, thanks. PostgreSQL is used on some of the biggest databases in the world, but no one's going to tell you which. :)
Your benchmark is pretty much irrelevant because Clustrix sells hardware appliances, not the software standalone.
Edit: That's not to say MongoDB didn't fail your benchmark. But the issues you highlight (single mutex) are known. Test against a real database and your results don't look that impressive for a 10 node setup.
All that said, Clustrix looks great. Just make it available sans-hardware.
Last time I heard, twitter still uses MySQL for the statuses (tweets) table. They did have a plan to migrate to Cassandra, but didn't go all the way through with it. So I find it hard to agree with "you just can't scale those". It may be a lot of work, but for some applications you can scale them.
It's worth noting that Twitter has built a lot on top of MySQL to get to the scale they're at. Take FlockDB for example, https://github.com/twitter/flockdb
So I guess that statement should be written as "you can't scale with just those". :)
You can't scale MySQL/PostgreSQL? Care to expand? (Although Facebook's schema is likely an abomination flying in the face of every normalized form, it does run on MySQL. And it's not like throwing PostgreSQL on a big box doesn't go far.)
Your benchmark is pretty much irrelevant because Clustrix sells hardware appliances, not the software standalone.
Edit: That's not to say MongoDB didn't fail your benchmark. But the issues you highlight (single mutex) are known. Test against a real database and your results don't look that impressive for a 10 node setup.
All that said, Clustrix looks great. Just make it available sans-hardware.