Incident: Checkout Latency Spike

Date: 2026-04-09 Service: Checkout Severity: Sev2

Checkout p95 latency increased from 480 ms to 4.8 s during a flash sale. Inventory reservation calls saturated the warehouse synchronization database connection pool, causing Checkout retries to amplify load.

Mitigation disabled aggressive client retry behavior and raised the Inventory read-replica pool limit. Follow-up work added queue-based reservation smoothing and a release readiness check for pool pressure.