Is it possible to implement Multi-Version Concurrency Control (MVCC) on top of MongoDB?

Question

MongoDB is to me a great database. However there are cases where I really need atomic multi-document transactions. For example to transfer things (like money or reputation)

Answer 1

The simplest way is to use locks (two-phase commit), although this is not very efficient in some cases. For higher concurrency some kind of MVCC can be implemented on the top of Mongo. This article provides a good description:

http://highlyscalable.wordpress.com/2012/01/07/mvcc-transactions-key-value/