A deep dive into the algorithm that lets systems like Cassandra and Amazon's Dynamo route keys without reshuffling the entire keyspace when nodes come and go.
The canonical system-design interview, built end to end: how tiny.co/aB3xK9 becomes a database lookup in single-digit milliseconds — base62, key generation, the read-heavy cache, and the scale math that makes 7 characters last a century.
Picking token bucket vs sliding window is the easy part. The real interview is what happens when the limiter runs on fifty machines: where the counter lives, why 'local counters' quietly lets 50× your limit through, and how to enforce one global cap without a round-trip on every request.
Auto-increment doesn't survive sharding, and random UUIDs wreck your database's index. How do you mint billions of unique, roughly time-sortable 64-bit IDs across a fleet with no coordinator? This is the Snowflake design — bit for bit.
The capstone that ties the whole series together: consistent hashing to place data, quorums to tune consistency, vector clocks to detect conflicts, and hinted handoff to stay writable through failure. This is Amazon's Dynamo, rebuilt from its four moving parts.