Consistent Hashing, eviction policies (LRU/LFU), and defeating the cache stampede and thundering herd problems.

Fan-out on write vs fan-out on read architectures. Optimizing for celebrity users with millions of followers.

Real-time messaging with WebSockets, presence servers, and message queues for offline delivery guaranteed.

CAP theorem analysis, DynamoDB architecture, Vector Clocks for conflict resolution, and Gossip protocol internals.

Discussing QuadTrees, Geohashing, and handling high-throughput location updates from millions of drivers.

Handling massive traffic spikes for popular concerts and preventing double-booking with DB locks.

Object-Oriented Design exercise: ParkingSpot, Level, Vehicle, Ticket, and Payment classes with clean interfaces.

Comparing Token Bucket, Leaky Bucket, and Sliding Window algorithms. Distributed rate limiting with Redis.

Base62 encoding, distributed ID generation with ZooKeeper, and handling read-heavy vs write-heavy workloads.