Why is checkout slow?
Customers report that an online checkout is slow. Server averages look normal, but completed purchases have fallen. What measurements would distinguish a server problem from a user-experience problem?
Real World challenge at hard difficulty.
Hint
Averages hide tails and a checkout has more than one stage.
Answer and method
Measure each step separately: client rendering, input delay, API latency percentiles, payment-provider time, validation errors, and abandonment by device and browser. Replay a synthetic checkout from representative regions. The shape of the funnel and the slowest percentiles will locate the failure more reliably than one server average.
Reusable reasoning moveMeasure the user's path and the distribution, not only the system-wide mean.