1. A system comprising: at least one processor; an optimizer executable by the at least one processor to determine a first distribution of successive operations among a plurality of execution environments based on a presumed status of the execution environments so as to achieve a performance objective; a scheduler executable by the at least one processor to: determine whether an actual status of the execution environments renders the first distribution suboptimal for achieving the performance objective, and request alternative distributions in response to determining that the actual status renders the first distribution suboptimal; the optimizer executable by the at least one processor to, in response to the request, determine the alternative distributions of the successive operations among the plurality of execution environments, and rank each respective alternative distribution of the alternative distributions in accordance with a potential of the respective alternative distribution to meet the performance objective given the actual status; and a dispatcher executable by the at least one processor to ensure the successive operations are executed in a predetermined order.