Queues & Backpressure

Putting work on a queue converts a synchronous dependency into an asynchronous one. The admission request can return once the job is durably enqueued, so a slow downstream leaves the user waiting for completion later rather than holding the original connection open.

Queues also provide buffering, ownership transfer, and retry boundaries, but a queue does not process anything. If work arrives at 1,200 jobs per second and workers manage 800, it accumulates the 400/s deficit for as long as the imbalance lasts.

The distinction is between a burst and a deficit. A burst is temporary: arrivals exceed capacity for a while, the queue absorbs the excess, and it drains once the spike passes. That is what queues are for. A deficit is structural, and a queue turns it from an immediate error into a backlog that grows until something else breaks.