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https://issues.apache.org/jira/browse/FLINK-10050?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16591511#comment-16591511
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eugen yushin commented on FLINK-10050:
--------------------------------------
[~aljoscha] There's no info about windows for any of operator in Flink. Docs:
https://ci.apache.org/projects/flink/flink-docs-release-1.6/dev/stream/operators/windows.html#working-with-window-results
```
The result of a windowed operation is again a {{DataStream}}, no information
about the windowed operations is retained in the result elements
```
At the same time, coGroup/join keeps element's timestamps and consecutive
operators can assign elements to respective windows. Docs:
[https://ci.apache.org/projects/flink/flink-docs-release-1.6/dev/stream/operators/joining.html#window-join]
```
Those elements that do get joined will have as their timestamp the largest
timestamp that still lies in the respective window. For example a window with
{{[5, 10)}} as its boundaries would result in the joined elements having 9 as
their timestamp.
```
Business case: 2 streams, 1 for different business metrics, another one -
similar metrics but from microservices logs, result - reconciliation of these 2
streams. No other operators except sink are need for this particular business
case.
> Support 'allowedLateness' in CoGroupedStreams
> ---------------------------------------------
>
> Key: FLINK-10050
> URL: https://issues.apache.org/jira/browse/FLINK-10050
> Project: Flink
> Issue Type: Improvement
> Components: Streaming
> Affects Versions: 1.5.1, 1.6.0
> Reporter: eugen yushin
> Priority: Major
> Labels: ready-to-commit, windows
>
> WindowedStream has a support of 'allowedLateness' feature, while
> CoGroupedStreams are not. At the mean time, WindowedStream is an inner part
> of CoGroupedStreams and all main functionality (like evictor/trigger/...) is
> simply delegated to WindowedStream.
> There's no chance to operate with late arriving data from previous steps in
> cogroups (and joins). Consider the following flow:
> a. read data from source1 -> aggregate data with allowed lateness
> b. read data from source2 -> aggregate data with allowed lateness
> c. cogroup/join streams a and b, and compare aggregated values
> Step c doesn't accept any late data from steps a/b due to lack of
> `allowedLateness` API call in CoGroupedStreams.java.
> Scope: add method `WithWindow.allowedLateness` to Java API
> (flink-streaming-java) and extend scala API (flink-streaming-scala).
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