HLD-323·Transactions & Locking
Hard · 1,500 ptsHigh-Concurrency Timed Online Auction & Sniping Guard
Design eBay / StockX’s live auction bidding backend where thousands of bidders fire last-second "snipe" bids on the same closing lot with strict monotonic high-bid ordering.
Max p99
≤ 110 ms
Availability
≥ 99.4%
Budget
≤ $7,900
Functional Requirements
- FR-1POST /auctions/{auction_id}/bids — Atomically validates `bid > current_high_bid` and extends soft-close timer.
- FR-2GET /auctions/{auction_id} — Returns authoritative current high bid, bidder alias, and remaining milliseconds.
- FR-3DELETE /auctions/{auction_id}/bids — Releases canceled or expired leases/holds atomically and immediately refreshes cached availability.
- FR-4Must never accept a lower bid over a higher bid or lose winning bids on primary DB crash.
Workload Profile
Active Browsing36,000 Watch Read RPS / 4,500 Bid Write RPS
Final-10s Sniping Frenzy96,000 Read RPS / 25,000 Concurrent Bid RPS
Active Working Set18 GB closing auction books & escrow holds
Contention ProfileExtreme write serialization on rare collectible auction_id lots
Consistency Model
Strict linearizable/serializable monotonic high-bid CAS + RPO = 0 quorum replication.
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