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https://issues.apache.org/jira/browse/FLINK-3255?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15106759#comment-15106759
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ASF GitHub Bot commented on FLINK-3255:
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Github user StephanEwen commented on the pull request:
https://github.com/apache/flink/pull/1518#issuecomment-172863106
I think this is expected and similar to the behavior of the batch API.
Two operators are connected with "forward" if they have the same
parallelism, and with "rebalance" if not. Since the source is forced to
parallelism 1 (non parallel collection), a parallelism 2 program needs to
rebalance.
I would leave that as it is.
> Chaining behavior should not depend on parallelism
> --------------------------------------------------
>
> Key: FLINK-3255
> URL: https://issues.apache.org/jira/browse/FLINK-3255
> Project: Flink
> Issue Type: Bug
> Components: Streaming
> Affects Versions: 1.0.0
> Reporter: Stephan Ewen
> Assignee: Stephan Ewen
> Fix For: 0.10.1
>
>
> Currently, operators are chained more aggressively when the parallelism is
> one. That makes debugging tougher as it changes threading behavior.
> The benefits are also limited: Real installations where that type of
> efficiency would be needed would not run in parallelism 1, or would not use a
> partitioning/broadcast step there (if explicitly required to run parallelism
> 1).
> In the future, when we want to allow parallelism to be adjusted dynamically,
> this will be even more tricky.
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