Design a Per-Key Ordered Queue · System Design Interview

Design a Per-Key Ordered QueueDesign a queue that keeps messages for the same key in order and processes them one at a time, while messages for different keys run in parallel across the fleet.What it has to do

Two messages with the same key are processed in the order they were published, never at the same time

Messages with different keys are processed concurrently

A slow or failing key does not stop the other keys

Scale

Messages per day: 80 billion

Distinct keys: 4 billion

Out of scope

The broker’s storage layout

What the consumer does with a message

Schema management

Practise this challengeAll system design challenges

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