Methods and apparatus, including computer program products, implementing and using techniques for processing an ordered sequence of elements in one or more queues. A first element is received from a queue at a first processor. The first element is processed during a first processing time. A second element is received from a queue at a second processor. The second element is processed during a second processing time. The first and second processed elements are committed serially to a write queue, such that a temporal order between the first and second elements in the queues is maintained regardless of the durations of the first and second processing times.