Data engineering·Time and correctness in streams
the phone was in a tunnel, so the tap happened at 14:02 and your job saw it at 16:40, and the hourly chart has to put it at 14:00.
Event time
Also calledsource time, occurrence time
The moment the thing actually happened, carried on the record itself. Every result that is supposed to be stable — yesterday's totals, an hourly chart, a session length — has to be computed on event time, because processing time changes if you re-run the job. It is also the harder clock: it arrives out of order, it can be arbitrarily late, and it is only as trustworthy as the device that stamped it.