TL;DR — Distributed Key-Value Store

Design a distributed key-value store like Amazon DynamoDB or Apache Cassandra. The system must store billions of key-value pairs across hundreds of nodes, providing single-digit millisecond read and write latency with tunable consistency. Each node should be able to handle failures independently without a single point of failure. Key features: PUT(key, value) — store a key-value pair. GET(key) — retrieve value by key.