HLD-208·Storage & Caching
Medium · 1,000 ptsCross-Device Video & Podcast Resume Sync
Design a playback-position bookmarking service persisting frequent player heartbeats so users switching from TV to mobile resume at the exact second.
Max p99
≤ 38 ms
Availability
≥ 99.5%
Budget
≤ $4,200
Functional Requirements
- FR-1PUT /progress/{user_id} — Checkpoints current media_id timestamp offset every 10 seconds.
- FR-2GET /progress/{user_id} — Returns latest watch/listen offsets across a user library.
- FR-3PATCH & DELETE /progress/{user_id} — Updates, cancels, or deletes user_id records and immediately invalidates or updates cached state (read-after-write).
- FR-4Switching devices must immediately return the latest checkpoint (read-after-write).
Workload Profile
Baseline Streaming28,000 Read RPS / 9,500 Checkpoint Write RPS
Prime-Time Premiere80,000 Read RPS / 26,000 Write RPS
Active Working Set18 GB active viewer session offsets
Traffic DistributionUniformly distributed per active user_id
Consistency Model
Read-after-write consistency required per user_id so cross-device handoff never rewinds to stale cache.
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