HLD-233·Caching & Consistency
Medium · 1,000 ptsSmart Airport & Stadium Garage Spot Reservation Service
Design a multi-garage smart parking availability and pre-booking backend ingesting gate-loop sensor events and serving live lot occupancy.
Max p99
≤ 52 ms
Availability
≥ 99.5%
Budget
≤ $5,200
Functional Requirements
- FR-1GET /garages/{garage_id}/availability — Returns real-time open stalls by level and EV/accessible type.
- FR-2POST /garages/{garage_id}/bookings — Reserves a parking pass and updates live stall counters.
- FR-3DELETE /garages/{garage_id}/availability — Supports tenant retention TTL expiry, rule updates, or stream cleanup while keeping recent rollup caches fresh.
- FR-4Must maintain read-after-write booking visibility and survive primary DB failover.
Workload Profile
Steady Commuter Load22,000 Read RPS / 3,500 Sensor & Booking RPS
Game-Day Stadium Arrival64,000 Read RPS / 11,000 Write RPS
Active Working Set14 GB live garage floor & reservation state
Traffic DistributionHeavy hotspot on event-day stadium/airport garage_id
Consistency Model
Read-after-write consistency on reserved passes and gate entry QR checks.
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Design Write-up
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