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https://issues.apache.org/jira/browse/FLINK-7567?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16155310#comment-16155310
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Mikhail Lipkovich commented on FLINK-7567:
------------------------------------------

I guess removing of parameter can be dangerous since it breaks the current API? 
But if you think it's fine I can assign this task to myself and remove it.
Regarding to message I thought about adding the way to resolve the issue. 
Something like
"Parallelism of original stream: 1; parallelism of feedback stream: 8. 
Parallelism can be modified using DataStream#setParallelism() method" 

> DataStream#iterate() on env.fromElements() / env.fromCollection() does not 
> work
> -------------------------------------------------------------------------------
>
>                 Key: FLINK-7567
>                 URL: https://issues.apache.org/jira/browse/FLINK-7567
>             Project: Flink
>          Issue Type: Bug
>          Components: DataStream API
>    Affects Versions: 1.3.2
>         Environment: OS X 10.12.6, Oracle JDK 1.8.0_144, Flink 1.3.2
>            Reporter: Peter Ertl
>
> When I try to execute this simple snippet of code
> {code}
>   @Test
>   def iterateOnElements(): Unit = {
>     val env = StreamExecutionEnvironment.getExecutionEnvironment
>     // do something silly just do get iteration going ...
>     val result = env.fromElements(1, 2, 3).iterate(it => {
>       (it.filter(_ > 0).map(_ - 1), it.filter(_ > 0).map(_ => 'x'))
>     })
>     result.print()
>     env.execute()
>   }
> {code}
> I get the following exception:
> {code}
> java.lang.UnsupportedOperationException: Parallelism of the feedback stream 
> must match the parallelism of the original stream. Parallelism of original 
> stream: 1; parallelism of feedback stream: 8
>       at 
> org.apache.flink.streaming.api.transformations.FeedbackTransformation.addFeedbackEdge(FeedbackTransformation.java:87)
>       at 
> org.apache.flink.streaming.api.datastream.IterativeStream.closeWith(IterativeStream.java:77)
>       at 
> org.apache.flink.streaming.api.scala.DataStream.iterate(DataStream.scala:519)
>       at atp.analytics.CassandraReadTest.iterate2(CassandraReadTest.scala:134)
>       at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
>       at 
> sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
>       at 
> sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
>       at java.lang.reflect.Method.invoke(Method.java:498)
>       at 
> org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
>       at 
> org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
>       at 
> org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
>       at 
> org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
>       at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
>       at 
> org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
>       at 
> org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
>       at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
>       at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
>       at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
>       at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
>       at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
>       at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
>       at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
>       at 
> com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
>       at 
> com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:47)
>       at 
> com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242)
>       at 
> com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)
> {code}
> Since is just the simplest iterating stream setup I could imagine this error 
> makes no sense to me :-P



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