An apparatus comprising: processing circuitry to process instructions from one of a plurality of software execution environments; and a memory system component (24, 100) to handle memory transactions issued by the processing circuitry in response to the instructions; in which: in response to a memory transaction issued by the processing circuitry specifying a partition identifier selected depending on which software execution environment caused the memory transaction to be issued, the memory system component is configured to control allocation of resources for handling the memory transaction or manage contention for said resources depending on a selected set of one or more memory system component resource control parameters (108, 400), said selected set selected from among a plurality of sets of one or more memory system component resource control parameters depending on the partition identifier specified by the memory transaction; the memory system component comprises programmable constraint storage circuitry to store at least one resource control parameter constraint; and based on said at least one resource control parameter constraint stored in said programmable constraint storage circuitry, the memory system component is configured to constrain at least one of: updating of a target memory system component resource control parameter; and usage of the target memory system component resource control parameter for controlling said allocation of resources or managing contention for said resources. processing circuitry to process instructions from one of a plurality of software execution environments; and a memory system component (24, 100) to handle memory transactions issued by the processing circuitry in response to the instructions; in which: in response to a memory transaction issued by the processing circuitry specifying a partition identifier selected depending on which software execution environment caused the memory transaction to be issued, the memory system component is configured to control allocation of resources for handling the memory transaction or manage contention for said resources depending on a selected set of one or more memory system component resource control parameters (108, 400), said selected set selected from among a plurality of sets of one or more memory system component resource control parameters depending on the partition identifier specified by the memory transaction; the memory system component comprises programmable constraint storage circuitry to store at least one resource control parameter constraint; and based on said at least one resource control parameter constraint stored in said programmable constraint storage circuitry, the memory system component is configured to constrain at least one of: updating of a target memory system component resource control parameter; and usage of the target memory system component resource control parameter for controlling said allocation of resources or managing contention for said resources. in response to a memory transaction issued by the processing circuitry specifying a partition identifier selected depending on which software execution environment caused the memory transaction to be issued, the memory system component is configured to control allocation of resources for handling the memory transaction or manage contention for said resources depending on a selected set of one or more memory system component resource control parameters (108, 400), said selected set selected from among a plurality of sets of one or more memory system component resource control parameters depending on the partition identifier specified by the memory transaction; the memory system component comprises programmable constraint storage circuitry to store at least one resource control parameter constraint; and based on said at least one resource control parameter constraint stored in said programmable constraint storage circuitry, the memory system component is configured to constrain at least one of: updating of a target memory system component resource control parameter; and usage of the target memory system component resource control parameter for controlling said allocation of resources or managing contention for said resources. updating of a target memory system component resource control parameter; and usage of the target memory system component resource control parameter for controlling said allocation of resources or managing contention for said resources.