A system including instructions recorded on a computer-readable medium, the system comprising: a sampler configured to determine a first performance measurement of an executing task, while the task is executed by a first number of nodes operating in 5 parallel, and configured to determine a second performance measurement of the executing task, while the task is being executed by a second number of nodes operating in parallel, wherein the sampler comprises an adjustment manager configured to determine and execute an adjustment from the first number of nodes to the second number of nodes after the determination of the first performance measurement, including determining a fixed number of nodes and determining whether to increase or decrease the first number of nodes by the fixed number of nodes to obtain the second number of nodes; and a calibrator configured to calculate an overhead factor characterizing a change of a parallelism overhead of executing the task with nodes executing in parallel, relative to a change in a number of the nodes, based on the first performance measurement and the second performance measurement, and configured to determine an optimal number of nodes to operate in parallel to continue executing the task, based on the overhead factor, wherein the calibrator is configured to instruct a resource scheduler to assign the optimal number of nodes for execution of the task therewith, wherein determination of the optimal number of nodes represents an end of a current sampling-then-calibrating operation, the system further comprising: a calibrating duration controller configured to control a time interval between the current sampling-then-calibrating operation and a subsequent sampling-then-calibrating operation, wherein the calibrating duration controller is configured to determine the time interval based on a change in the optimal number of nodes of the current sampling-then-calibrating operation and at least one previously-determined optimal number of nodes of at least one previous sampling-then-calibrating operation, wherein the calibrating duration controller is configured to increase the time interval if little or no change in the optimal number of nodes occurred, wherein the calibrating duration controller is configured to decrease the time interval if a large change in the optimal number of nodes occurred. a sampler configured to determine a first performance measurement of an executing task, while the task is executed by a first number of nodes operating in 5 parallel, and configured to determine a second performance measurement of the executing task, while the task is being executed by a second number of nodes operating in parallel, wherein the sampler comprises an adjustment manager configured to determine and execute an adjustment from the first number of nodes to the second number of nodes after the determination of the first performance measurement, including determining a fixed number of nodes and determining whether to increase or decrease the first number of nodes by the fixed number of nodes to obtain the second number of nodes; and a calibrator configured to calculate an overhead factor characterizing a change of a parallelism overhead of executing the task with nodes executing in parallel, relative to a change in a number of the nodes, based on the first performance measurement and the second performance measurement, and configured to determine an optimal number of nodes to operate in parallel to continue executing the task, based on the overhead factor, wherein the calibrator is configured to instruct a resource scheduler to assign the optimal number of nodes for execution of the task therewith, wherein determination of the optimal number of nodes represents an end of a current sampling-then-calibrating operation, the system further comprising: a calibrating duration controller configured to control a time interval between the current sampling-then-calibrating operation and a subsequent sampling-then-calibrating operation, wherein the calibrating duration controller is configured to determine the time interval based on a change in the optimal number of nodes of the current sampling-then-calibrating operation and at least one previously-determined optimal number of nodes of at least one previous sampling-then-calibrating operation, wherein the calibrating duration controller is configured to increase the time interval if little or no change in the optimal number of nodes occurred, wherein the calibrating duration controller is configured to decrease the time interval if a large change in the optimal number of nodes occurred. a calibrating duration controller configured to control a time interval between the current sampling-then-calibrating operation and a subsequent sampling-then-calibrating operation, wherein the calibrating duration controller is configured to determine the time interval based on a change in the optimal number of nodes of the current sampling-then-calibrating operation and at least one previously-determined optimal number of nodes of at least one previous sampling-then-calibrating operation, wherein the calibrating duration controller is configured to increase the time interval if little or no change in the optimal number of nodes occurred, wherein the calibrating duration controller is configured to decrease the time interval if a large change in the optimal number of nodes occurred.