What is Backpressure?
Backpressure, told as a story about an entrance that slows down the moment the inner booth fills up.
Guests rush in all at once, and even the inner booth fills up.The inner booth is so busy the line stretches back to the entrance.
If the inside is busy but the entrance keeps admitting more, everyone slows down together.Guests start stacking up from the inside out, until the whole park slows.
When the inside is full, the entrance slows down first.Better than admitting everyone and bursting later.
The full signal must reach the entrance so it can slow down in advance.Without the signal, the entrance keeps admitting guests until everything stops at once.
Block the entrance too hard, and guests leave for another park entirely.Finding the right amount is hard — slow it too much and you lose guests.
Backpressure = when the inner booth is full, the entrance slows down in advance — not stopping entirely, just letting a trickle through.
A flow-control technique: when a downstream stage is overwhelmed, the upstream slows its own rate. The full state is called saturation, and the signal travels back upstream through whatever carries it — a queue, a connection. Throttle too hard and throughput collapses, so tuning the degree matters.
When grown-ups say it
- Backpressure
- The entrance slowing itself down when the inside is full. Not a full stop — just a trickle through.
- Flow control
- Adjusting the sender's pace to match the receiver's. Backpressure is one way to do flow control.
- Overload
- More coming in than can be handled. Noticing overload early is where backpressure starts.
- Saturation
- The inner booth being as full as it can get. One of the four gauges the control room always watches.
- Rate limiting
- A rule capping how many get in at once. Backpressure slows itself based on inner state; rate limiting caps at a number fixed in advance — similar, but the signal comes from a different place.
- Queue
- The line piling up in front of a booth. The backpressure signal usually comes from watching how long this line gets.
- Graceful degradation
- Cutting back some features to stay open at all, when things get hard. The next move when backpressure alone isn't enough.
- Circuit breaker
- The red button that stops sending guests somewhere entirely broken. Backpressure slows things down; this cuts them off entirely. → the red button you press when something breaks