apache / apache/beam

Using Merging Windows and/or Triggers without a downstream aggregation should fail

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backward-incompatible bug core java P3
Dominant language
Java
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Description

Both merging windows (such as sessions) and triggering only actually happen at an aggregation (GroupByKey). We should produce errors in any of these cases:

1. Merging window used without a downstream GroupByKey
2. Triggers used without a downstream GroupByKey
3. Window inspected after inserting a merging window and before the GroupByKey

Imported from Jira [BEAM-184](https://issues.apache.org/jira/browse/BEAM-184). Original Jira may contain additional context.
Reported by: bchambers.

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Research direction

No source files or tests are named. Start by locating the validation paths for merging windows, triggers, and downstream GroupByKey, then reproduce the three cases listed in the issue. Done means each invalid pipeline is rejected with an error, including inspecting a window before GroupByKey.

Written by the indexing model from the issue text.

Assessment

Tech stack
java
Domain
stream-processing
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
35/100

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