Data engineering·Time and correctness in streams
the window emitted a result at 15:00 and keeps updating it for another two hours before it finally throws the state away.
Allowed lateness
Also calledlateness grace period, grace period
How long after a window closes the job will still accept and re-emit for records belonging to it. It buys correctness with memory and with downstream churn — every update is a rewrite somebody has to handle — and it is bounded because state cannot be kept forever. Setting it is a business conversation dressed as a config value: how wrong may this number be for how long, and can the consumer cope with it changing.