Comparison
Late-arriving datavsLate-arriving dimension
Late-arriving data
yesterday's total went up this morning, because eight hundred events from a phone that was offline finally arrived.
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.
Full entry →Late-arriving dimension
the order arrived before the customer record did, so the fact points at a placeholder row labelled unknown.
A fact whose dimension row does not exist yet at load time, usually because two source systems publish at different speeds. The standard handling is an inferred member — insert a stub dimension row keyed on the business key and fill in its attributes when the real record shows up. Doing nothing instead means either dropping the fact or breaking the join, and both are worse than a temporary unknown.
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