lastacknowledged

Lastacknowledged is a term used in computing to denote the most recent data unit, such as a packet, frame, or log entry, that has been confirmed as received by the counterparty. It serves as a reference point for monitoring progress, reliability, and retransmission decisions in communication and storage systems. In reliable transfer, the sender tracks data up to the last acknowledged position, advancing its send window only when acknowledgments arrive. The receiver communicates the last acknowledged position to indicate up to which data has been received in order, and, in some protocols, to reveal gaps through additional signaling.

In network protocols, acknowledgments confirm receipt and help control flow. The last acknowledged boundary defines which data is considered successfully delivered. Some systems use cumulative acknowledgments, while others employ selective acknowledgments to describe non-contiguous received segments. The concept is central to mechanisms such as sliding windows, retransmission timeouts, and congestion control, where progress or stall is inferred from changes in the last acknowledged value.

In distributed systems and log-based replication, last acknowledged (or last acknowledged offset) indicates how far a replica has durably stored or confirmed. Writers may wait for acknowledgments from a quorum to ensure durability and consistency before advancing. This boundary is critical for recovery after failures and for maintaining data integrity across replicas.

Common considerations include latency effects on acknowledgment timing, the handling of out-of-order delivery, and the potential for duplicate deliveries in asynchronous environments. See also acknowledgment, TCP, ARQ, sliding window, selective acknowledgment, and log replication concepts.