Data engineering·Time and correctness in streams
you need the click matched to the impression, and one of them is always five minutes behind the other.
Streaming join
Also calledstream-stream join, windowed join
Joining two unbounded inputs, which requires holding one side's records in state long enough for the other side to show up. That retention window is the join's cost and its correctness bound at the same time: too short and you miss real matches, too long and state grows without limit. Unlike a batch join, an unmatched row is not necessarily a data error — it may simply be early.