Backpressure

Backpressure is the signal a slow consumer sends upstream when it cannot keep up: stop sending, or send less. Without it a producer keeps pushing into a queue that grows until memory runs out, and the failure arrives all at once rather than gradually. With it, the system has a stated behavior under load - buffer to a limit, then slow the producer, then shed defined work - which is the difference between degradation you planned and an outage you discover.

Real-time data makes the choice sharper, because buffering is itself a cost: a record held for ten seconds to avoid dropping it may be worthless by the time it lands. The design question is therefore not whether to drop but what to drop, and evaluating urgency in flight is what allows a network to answer it - the highest-signal records keep moving while low-value volume waits. Whatever the policy, it belongs in the delivery guarantee the consumer reads, not in an incident report after the fact.