ex-Percona MySQL wizard Baron Schwartz, noting that MVCC as implemented in common SQL databases is not all that simple or reliable compared to big bad NoSQL Eventual Consistency:

Since I am not ready to assert that there’s a distributed system I know to be better and simpler than eventually consistent datastores, and since I certainly know that InnoDB’s MVCC implementation is full of complexities, for right now I am probably in the same position most of my readers are: the two viable choices seem to be single-node MVCC and multi-node eventual consistency. And I don’t think MVCC is the simpler paradigm of the two.