Expert
Exactly-once at 8,000 transfers per second
A payments app processes peer-to-peer transfers asynchronously. The team picked a FIFO queue for its exactly-once guarantee, but at 8,000 transfers per second the API is now being throttled. Apply every transfer exactly once, keep up with the flow and stay within a monthly budget of 22,000 dollars.
A FIFO queue accepts about 3,000 messages per second. Standard queues and event logs deliver at least once, so a message can arrive twice. Transfers of one account must stay in order. Queues are billed per message, logs per partition and broker. The ledger is fixed: change what feeds it.
What your design must achieve
- Duplicated side effects = 0
- Availability ≥ 99.9 %
- Worst queue lag < 60 s
- Writes p99 < 150 ms
- Monthly bill < 22,000 $