We address the problem of building scalable transaction management mechanisms for multi-row transactions on key-value storage systems. We develop scalable techniques for transaction management utilizing the snapshot isolation (SI)model. Because the SI model can lead to non-serializable transaction executions, we investigate two conflict detection techniques for ensuring serializability under SI. To support scalability, we investigate system models and mechanisms in which the transaction management functions are decoupled from the storage system and integrated with the application-level processes. We present two system models and demonstrate their scalability under the scale-out paradigm of Cloud computing platforms. In the first system model, all transaction management functions are executed in a fully decentralized manner by the application processes. The second model is based on a hybrid approach in which the conflict detection techniques are implemented by a dedicated service. We performa comparative evaluation of these models using the TPC-Cbenchmark and demonstrate their scalability.