HLD-216·Messaging & Queues
Medium · 1,000 ptsFlight & Retail Price-Drop Watchlist Matcher
Design a price-tracking alert service matching continuous airline and retail fare repricing streams against millions of user target-price watchlists.
Max p99
≤ 58 ms
Availability
≥ 99.5%
Budget
≤ $5,100
Functional Requirements
- FR-1POST /fares/{route_id} — Ingests live supplier price updates and triggers threshold matching.
- FR-2GET /watches/{route_id} — Queries active user target thresholds and recent route price history.
- FR-3PATCH & DELETE /fares/{route_id} — Updates, revokes, or deletes route_id entries with bounded TTL or explicit cache/index invalidation.
- FR-4Must decouple flash-sale repricing floods and survive 6x backing storage latency brownouts.
Workload Profile
Baseline Feeds28,000 Read RPS / 10,000 Fare Write RPS
Flash-Fare Flood74,000 Read RPS / 30,000 Write RPS
Active Working Set26 GB active route watchlists & min-price state
Traffic DistributionSkewed updates on popular holiday route_id corridors
Consistency Model
Eventual alert evaluation (< 5s) acceptable; fare updates and user watch subscriptions must persist durably.
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