Evaluation of YouTube's Design

Evaluate the proposed video service through playback quality, durability, and recovery. Then examine the costs of caching, replication, deduplication, and sharded metadata storage.

Requirements compliance

Assess four requirements: playback performance, scalability, availability, and reliability.

1. Low latency and smooth playback: Nearby CDN/ISP caches reduce delivery distance and origin load. Metadata indexes and caches reduce lookup work, while prepared renditions support adaptive playback. Cache storage may use memory or disks. Measure startup delay, rebuffering, and delivered quality rather than inferring success from component names.

2. Scalability: Scale application instances, encoders, storage, and delivery links according to their separate workloads. Partition metadata when a measured write, storage, or query limit requires it.

3. Availability: Maintain healthy alternatives for media delivery, metadata, and routing. Test whether a node or site failure leaves enough capacity and a usable authorization path.

4. Reliability: Preserve acknowledged uploads and repair damaged or lost copies. Heartbeats detect suspected failures; consistent hashing can limit placement changes, but neither replaces data transfer, validation, or safe ownership changes.