Alignment Delay: Hidden Latency When Events Wait for Periodic Boundaries

Engineers often see system latency that exceeds expectations even without load, and the cause can be alignment delay, where asynchronous events must wait for the next tick of a periodic boundary such as a camera frame, cache TTL, or polling interval. Such a wait adds between zero and one period T of latency, averaging T/2. When several independent periodic stages exist, their average delays add together. In a live video example with 2-second segments, metadata takes about 2 seconds on average to reach players, with a worst case of 4 seconds. Where the boundaries are out of phase, the latency floor rises, as shown by an inference system whose 10fps cameras offset by 50ms produce a minimum added delay of 50ms instead of zero. The author suggests detecting it by instrumenting milestone arrival times and watching for delays averaging around T/2.