An apparatus is provided comprising processing circuitry to perform data processing in response to instructions of one of a plurality of software execution environments. At least one memory system component handles memory transactions for accessing data, with each memory transaction specifying a partition identifier allocated to a software execution environment associated with the memory transaction. The at least one memory system component is configured to select one of a plurality of sets of memory transaction progression parameters associated with the partition identifier specified by a memory transaction to be handled. Memory transaction progression control circuitry controls progression of the memory transaction in dependence on the selected set of memory transaction progression parameters.