This sounds like SQL ontop of Cassandra (for a more or less mental-map if you are looking for one):
Our distributed non-blocking atomic commit protocol allows database
transaction processing at any available node. The system is
designed to provide a consistent view of data, high availability,
and the ability to detect and manage partitions in a predictable
and consistent manner. Query processing scales with the number of
available nodes, storage scales according to the choice of storage
manager of which there are many. Storage managers are key/value
storage engines that also operate as a distributed in-memory cache
and participate in the commit protocol to ensure durability
guarantees.There is a general misconception that the an entire DBMS must pick tradeoffs based on the CAP theorem. (IE, you can use a database that offers availability, but can NEVER offer immediate consistency) Instead, a DBMS may offer different CAP guarantees per operation.
Another problem I can see is when you write to 3 nodes, have W=2 and a write succeeds only one one node. Then later on through read repair the value propagates to the other 2 nodes. So our write "failed" but really in the end succeeded. I'm not too much into the Cassandra details but those two things immediately came to my mind when reading some of the wiki pages.
It boils down to not using/offering algorithms like 2-Phase Commit or Paxos but more sloppy quorums.
So from what I can tell, Cassandra can not guarantee strong consistency. But then again I could be wrong and missed something.
"Note that if W + R > ReplicationFactor, where W is the number of nodes to block for on write, and R the number to block for on reads, you will have strongly consistent behavior; that is, readers will always see the most recent write."
Could you explain why this is incorrect? It seems the Cassandra devs use the definition of "consistency" from Brewer's paper, and Cassandra offers this level of consistency.
Your point about read-repair is correct when using QUORUM consistency level, but even then you can avoid that by using the ALL consistency level.
As for open source, something you can't say is that open source communities are unable to develop this kind of software.
Instead, read the 'who we are' and 'how it works' bits on NuoDB's page. They were much more informative.
I think it sounds exciting and fresh... And doesn't seem to be open source at all.
I'm not allergic to paying money for software, but I've found I'm happiest when using something that I can guarantee will survive, even if may have to do so by my own hand. Commercial products have a tendency to be a pain in the rear.