2:17 AM. I was blasted awake by a chain of alerts — the order service was frantically throwing “inventory deduction failed,” and the logs were drowning in KeyError . I jumped onto the Redis dashboard: memory usage was only 30%, but the inventory keys for dozens of hot products had simply vanished. Just yesterday we had rolled out the hybrid persistence strategy, thinking we could finally sleep soundly. That confidence was brutally shattered. After six hours of digging, the root cause surfaced: u