[wmf]

If you keep adding servers indefinitely, it becomes slower and slower to commit every transaction to every server.

The point of database partitioning is that a transaction that doesn't span partitions only touches a constant number of servers (usually 2 or 3).

[kennu]

I would interpret that as a compromise where C, A and P are divided into some ratio (you still don't get 100% of each). I understand Cassandra does that well if the application fits the model.