Consistent Hashing and Sharding

Sharding spreads data across nodes so no single machine holds everything, but naive modulo hashing remaps almost every key when you add or remove a node. Consistent hashing places nodes and keys on a hash ring so that adding or removing a node only reshuffles the keys near it, roughly K/N keys instead of all of them. Virtual nodes smooth out load imbalance. Applied-AI interviews probe it because vector indexes, KV caches, and feature stores are all sharded, and rebalancing cost is the difference between a rolling deploy and an outage.