Backpressure

Backpressure is a flow-control mechanism that prevents a fast producer from overwhelming a slow consumer. Instead of buffering unboundedly or dropping data, the consumer signals how much it can handle.

Akka Streams implements the Reactive Streams standard, where demand flows upstream and elements flow downstream.

Each stage only emits when the next stage has signalled demand. A Sink requests N elements; that demand propagates upstream until a Source produces exactly what was asked for.

This pull-based protocol means producers never push more than consumers can process.