backpressure

HTTP success can carry a rejected-span count. Replaying that batch can duplicate accepted telemetry, while enlarging the queue cannot repair invalid data.

Every overloaded system dies the same way: queues turn load into latency, latency into timeouts, timeouts into retry storms. Tiered shedding, deadline propagation, and retry budgets are the design.

A single FIFO queue is a first-come-first-served promise to whoever submits fastest. Fairness needs per-tenant queues and a scheduler that picks between them, and priority without fairness just moves the problem.