Denial-of-service attacks are prevented or mitigated in a cloud compute environment, such as a multi-tenant, collaborative SaaS system. This is achieved by providing a mechanism by which characterization of “legitimate” behavior is defined for accessor classes, preferably along with actions to be taken in the event an accessor exceeds those limits. A set of accessor “usage profiles” are generated. Typically, a profile comprises information, such as one or more “constraints,” and one or more “actions.” At least one constraint is generated by applying one or more parameters of a transaction weighting function such that the resulting constraint represents an actual or estimated cost of executing the transaction. An action defines how the system will respond if a particular constraint is triggered. By applying the constraints to accessor requests, the approach prevents over-utilization of compute resources.