Visualizers
Learn by moving things
Interactive explainers for the ideas behind retrieval, embeddings, and agents. A formula tells you what is true; dragging a vector shows you why. Each one also appears inside the article it belongs to, and runs entirely in your browser, so drag, poke, and break it.
Visibility timeout and at-least-once
From: Message Queues: Work That Waits Its Turn →A received message is hidden, not deleted, for a visibility timeout. If the worker crashes before acknowledging, the message reappears for another worker. Never lost, but it can run more than once, so keep workers idempotent.
A message waits on the queue, visible for any worker to take.
Dead-letter queue
From: Message Queues: Work That Waits Its Turn →A poison message that fails every time would redeliver forever and burn workers. After a set number of receives (the maxReceiveCount), it is moved to a dead-letter queue for inspection, and the main queue keeps flowing.
Order 999 points at a deleted product, so the worker throws every time. Attempt 1 of 5: it fails and reappears on the queue.
Fan-out: one event, many listeners
From: Pub/Sub: One Event, Many Listeners →A publisher posts one event to a topic, and every subscriber gets its own copy at the same moment: email, SMS, push, in-app. The publisher never knows who is listening, so adding a new channel is just one more subscriber.
An event happens: an order ships.