Retries and slow responses
The network drops in the middle of an operation. Press the button twice and see what ends up in the database — with an idempotency key and without one.
Tap a part of the diagram to open that step.
The whole picture
A key per operation turns a retry from a second charge into a read of a stored result. An asynchronous contract turns waiting into a subscription. Both are about the same thing: the network is unreliable, and that is the normal case rather than the exception.
What's inside
- 1 The request and the dropped connection — Turn on "break the network after the charge" and press the button twice.
- 2 What the server does — The key is invented by the client, one per operation, and repeated on every retry.
- 3 Without a key — duplicates — Retries are not only made by people: browsers, proxies and job queues make them too.
- 4 With a key — one record — The row is created before the action itself, otherwise two simultaneous retries race straight past each other.
- 5 A slow answer: 504 or 202 — Streaming needs proxy buffering switched off, otherwise the whole answer arrives in one lump at the end.
Explorable Explanations
- How a drug is smuggled past the blood–brain barrier The brain refuses almost every drug molecule, and it is right to. One slider follows the trick the labs are trying instead: wrap the molecule in a bubble the wall already knows how to carry.
- How a robot draws the map of a room it has never seen A lidar returns a few hundred dots per sweep and no idea where it is. One slider walks from that cloud to a floor plan with the robot standing in the right spot.
- How two people type in one line without losing a letter Two cursors, one line, nobody holding the pen in the middle. One slider takes an index-based merge apart and rebuilds it out of addresses that sit between the letters.
- Why a quantum computer stops at a lattice Shor’s algorithm eats RSA in one move. The same machine gets almost nothing on a grid of points with a little noise added. One slider shows the difference.
- Cooling a building by pointing it at space A coating that stays colder than the air around it, in full sun, drawing no power at all. One slider follows the heat from the sun to the far side of the atmosphere.
- How a robot predicts the next second A text model guesses the next word. A world model guesses the next frame — mass, speed and gravity included. One slider walks the whole loop, from the camera to the catch.
- Proving a secret without revealing it One slider walks through the stages, the other adds rounds. Watch certainty climb to almost total while the secret stays a secret.
- Getting lithium out of brine: ponds versus direct extraction Move the slider through five stages and compare two ways of taking the same metal out of the same salt water.
- How a personalised mRNA cancer vaccine works Move the slider through five stages and watch how a tumour’s own mutations become the instructions that teach the immune system to find it.
- The edge of the app Everything arriving from outside is untrusted. Break one link at a time and watch where the chain stops and what the screen shows.
- How search over your documents works Move the sliders and watch a search pipeline decide what the model is allowed to see — and what happens when it is fed the wrong passage.
- How a language model writes The weights are frozen and nothing is remembered. Pull the sliders and watch the model pick the next piece of text, over and over.
- How a language model learns Pull one slider and watch a pile of random numbers turn into a prediction over a thousand training steps.
- Where electricity comes from Pull one slider and follow the energy from a river all the way to a pump that lifts water back up.