Idempotency

Idempotency refers to the property of an operation where executing it multiple times with the same input produces the same result or state as executing it just once. In stream processing, idempotent operations (especially on sinks) are crucial for achieving effective exactly-once semantics, as they allow safe retries after failures without causing duplicate side effects. For example, writing results with a unique key that allows upserts is an idempotent operation.