Abstract: Transactional data accesses are performed in a data storage system, where the data storage system is configured to store a plurality of data objects identified by respective key values. A request is received to modify the value of a particular data object. The request specifies a modified object value and a key value identifying the data object to be modified. In response to the request, a transactional data object is created, the transactional data object specifying a transaction identifier, the original object value and the modified object value. The transactional data object is stored in the data storage system, and associated with the key value.