Pushing Back Upstream

A streaming ingestion service accepts events over a socket and hands them to a slower enrichment stage. The team says they have added backpressure. What does that actually mean in this pipeline?

The slow stage starts extra worker threads automatically whenever its input buffer begins to fill

The slow stage caps how much the fast stage may send, so its processing rate becomes the send rate

The fast stage buffers everything it produces in memory so the slow stage is never forced to stall

The broker quietly discards its oldest buffered events once the buffer hits its configured limit