When do you give ACK? Immediately upon receipt or after processing?

ACK (Acknowledgment) — confirmation of data receipt. Depending on the protocol and business logic, the timing of sending ACK may vary.

Sending ACK immediately upon receipt reduces delays and increases throughput, but risks confirming data that has not yet been processed or may cause errors.

Sending ACK after full processing guarantees that the data has been successfully processed, but increases delay and the risk of data re-sending in case of failures.

In systems with critical processing (e.g., financial transactions), it is better to confirm after processing to avoid data loss. In less critical cases or when high performance is required — immediately upon receipt.

The choice depends on reliability and performance requirements, as well as on the specifics of the protocol and system architecture.