[FLINK-19317] Make EventTime the default StreamTimeCharacteristic

• Type: Sub-task
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 1.12.0
• Component/s: API / DataStream
• Labels: pull-request-available
• Assignee: Aljoscha Krettek
• Reporter: Aljoscha Krettek
• Created: 21/Sep/20 09:07
• Updated: 05/Jun/22 03:49
• Resolved: 01/Oct/20 15:15

Description

Excerpt from FLIP-134:

As described above, event time is the only sensible time characteristic for batch. We therefore propose to change the default value of the StreamTimeCharacteristic from ProcessingTime to EventTime. This means the DataStream API programs that were using event time before now just work without manually changing this setting. Processing-time programs will also still work, because using processing-time timers is not dependent on the StreamTimeCharacteristic. DataStream programs that don't set a TimestampAssigner or WatermarkStrategy will also still work if they don't use operations that don't rely on (event-time) timestamps. This is true for both BATCH and STREAMING execution mode.

The only real user-visible change of this is that programs that used the KeyedStream.timeWindow()/DataStream.timeWindow() operation, which is dependent on the StreamTimeCharacteristic will now use event time by default. We don't think this operation is useful because the behaviour can be surprising. We recommend users always use an explicit processing-time window or event-time window.

Issue Links

• causes: FLINK-27890 SideOutputExample.java fails
• links to: GitHub Pull Request #13509