Load shedding
Deliberately rejecting less important requests when a service is overloaded, so the important ones still succeed.
Definition
Instead of queuing everything and timing out late, an overloaded service rejects work early with a cheap response (usually 503 with Retry-After), starting with low-priority requests such as prefetching or analytics. Signals for shedding include CPU, queue length and how long a request has already waited. Work for clients that have already given up is pure waste.
In practice
During a traffic spike, the API rejects background sync requests so checkout requests keep succeeding.