An apparatus comprises partition identifier storage storing an instruction partition identifier and a data partition identifier. When issuing a memory transaction for accessing data, the transaction is issued specifying a partition identifier depending on the data partition identifier, while when the memory transaction is for accessing an instruction, the transaction specifies a partition identifier depending on the instruction partition identifier. A memory system component selects one of a number of sets of memory system component parameters in dependence on the partition identifier specified by a memory transaction to be handled. The memory system component controls allocation of resources for handling the memory transaction or manages contention for the resources in dependence on the selected set of parameters, or updates performance monitoring data specified by the selected set of parameters in response to handling of said memory transaction.