[FLINK-22587] Support aggregations in batch mode with DataStream API

• Type: Bug
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 1.12.0, 1.13.0
• Component/s: API / DataStream
• Assignee: Unassigned
• Reporter: Etienne Chauchot
• Created: 06/May/21 12:20
• Updated: 08/Nov/22 15:50

Description

A pipeline like this in batch mode would output no data

stream.join(otherStream)
    .where(<KeySelector>)
    .equalTo(<KeySelector>)
    .window(GlobalWindows.create())
    .apply(<JoinFunction>)

Indeed the default trigger for GlobalWindow is NeverTrigger which never fires. If we set a EventTimeTrigger it will fire with every element as the watermark will be set to +INF (batch mode) and will pass the end of the global window with each new element. A ProcessingTimeTrigger never fires either and all elapsed time or delta based triggers would not be suited for batch.

Same goes for reduce() instead of join().

So I guess we miss something for batch support with DataStream.