Data engineering·Time and correctness in streams
yesterday's total went up this morning, because eight hundred events from a phone that was offline finally arrived.
Late-arriving data
Also calledlate data, late events
Records whose event time falls into a window that has already been computed. Every distributed source produces them — offline devices, retried deliveries, a partition that fell behind — so the question is never whether they exist but what you do with them: drop, count separately, or restate the window. Whichever you choose is visible to whoever reads the number, which is why it belongs in a conversation with them rather than in a config file.