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https://issues.apache.org/jira/browse/FLINK-10050?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16616225#comment-16616225
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ASF GitHub Bot commented on FLINK-10050:
----------------------------------------
EugeneYushin commented on a change in pull request #6646: [FLINK-10050] Support
allowedLateness in CoGroupedStreams
URL: https://github.com/apache/flink/pull/6646#discussion_r217879647
##########
File path:
flink-streaming-java/src/main/java/org/apache/flink/streaming/api/datastream/JoinedStreams.java
##########
@@ -239,7 +245,17 @@ protected WithWindow(DataStream<T1> input1,
@PublicEvolving
public WithWindow<T1, T2, KEY, W> evictor(Evictor<? super
TaggedUnion<T1, T2>, ? super W> newEvictor) {
return new WithWindow<>(input1, input2, keySelector1,
keySelector2, keyType,
- windowAssigner, trigger, newEvictor);
+ windowAssigner, trigger, newEvictor,
allowedLateness);
+ }
+
+ /**
+ * Sets the time by which elements are allowed to be late.
+ * @see WindowedStream#allowedLateness(Time)
+ */
+ @PublicEvolving
+ public WithWindow<T1, T2, KEY, W> allowedLateness(Time
newLateness) {
Review comment:
Check for null in this place breaks current logic of CoGroup/Join classes.
CoGroup has no checks for nulls directly in `evictor`/`trigger` methods and
validates during delegation:
https://github.com/apache/flink/blob/98412a5f7227d7694c727847727f9434bcca4e92/flink-streaming-java/src/main/java/org/apache/flink/streaming/api/datastream/CoGroupedStreams.java#L344
I do null check there as well for `allowedLateness` field.
In the same time, Join.apply delegates to CoGroup.apply:
https://github.com/apache/flink/blob/98412a5f7227d7694c727847727f9434bcca4e92/flink-streaming-java/src/main/java/org/apache/flink/streaming/api/datastream/JoinedStreams.java#L314).
To be consistent, we also should add null checks for evictor and trigger.
Adding null checks directly in setters/constructor breaks chain of calls in
`apply` methods (for evictor/trigger/allowedLateness) and requires clumsy
if-else conditions for each nullable field separately.
Both CoGroup and Join allow null for trigger/evictor (and I've added
allowedLateness following the same approach) but don't pass validation during
calls to `apply(...)`.
As a result of null check for `allowedLateness` inside setter, we have
errors for the following scenario:
https://github.com/apache/flink/blob/8674b69964eae50cad024f2c5caf92a71bf21a09/flink-streaming-scala/src/test/scala/org/apache/flink/streaming/api/scala/CoGroupJoinITCase.scala#L151
It breaks when user doesn't specify any of trigger/evictor/allowedLateness.
At the same time, these fields are optional and have defaults in
WindowedStream. Unfortunately, default for allowedLateness in WindowedStream
has private modificator (and I don't think it's a good practice to set default
when user passed null by mistake).
Please, let me know you thoughts.
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> 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: pull-request-available, 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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