Offset
A monotonically increasing integer that uniquely identifies a message's position within a Kafka partition. Consumer groups commit their current offset to track progress. Resetting an offset to an earlier position enables replay of historical events without re-publishing them.
The offset is Kafka's fundamental position marker. Every message appended to a partition receives the next integer offset in that partition's sequence. Consumer groups track their progress by committing the offset of the last successfully processed message. This committed position is durable: if a consumer restarts, it resumes from its last committed offset rather than the beginning of the topic. Offsets enable two important operational capabilities. First, at-least-once delivery: if a consumer crashes before committing, it re-processes messages from the last committed offset. Second, replay: by resetting a consumer group's offset to any historical position, operators can re-process old events without republishing them - useful for re-indexing after a schema change, re-running consolidation with new logic, or debugging a processing failure by replaying the events that caused it.