This is an interesting use of the HyperLogLog algorithm. And yay for less RAM overhead.

They are atomic, they are not isolated. Those are two different properties. The "A" vs the "I" in ACID. http://en.wikipedia.org/wiki/ACID

Edit: Actually, they are isolated in the sense of ACID, doesn't matter what order you do to operations, the answer will be the same. But not isolated the way you want isolated described.

The scenario that he's found is when the two timestamps are actually identical. In that scenario, Cassandra cannot maintain its atomicity guarantee.

No, they are not isolated in the sense of ACID. This behavior violates P0.

"Minutes" is not "unaffected" if your site is now down.

Sorry, I should have clarified. When a node goes down, there isn't any sort of "minute" interruption...When there's a full scale outage and you need to perform an actual recovery, that can take minutes.

This is the reason our company creates their own packages and runs our own repositories.

even if switch failures are rarer, couch at W=1 will silently drop data for network partition, dynamo at W=2 won't, how is the comparison at the end valid?

"...if the client wanted true multi-node durability, then the write wouldn't have succeeded (the client would timeout waiting for replicas(s) to receive the update) and the client wouldn't unknowingly lose data."

But that isn't W=1

Ok, you're right. I just changed it to W=2, and all the numbers are the same.