Event time.
also: event time vs processing time · event-timeWhen something actually happened, versus processing time, when the pipeline saw it; analytics must aggregate by event time.
the two-minute refresher
- A click at 14:30:00 can arrive at 14:30:05, or hours later from an offline phone.
- Grouping by arrival time puts events in the wrong window.
- The gap comes from network delays, retries, offline devices and backlogs.
- Watermarks track how far event time has progressed.