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From Paris Carbone <par...@kth.se>
Subject Re: Stream iteration head as ConnectedDataStream
Date Fri, 26 Jun 2015 15:21:28 GMT
That’s convenient, at least for the incremental ML where feedback streams are the norm.
In this case we don’t force the user to create wrappers and we also know what comes from

I went through the PR and it looks that doesn’t break anything so you have my +1.


> On 26 Jun 2015, at 13:35, Gyula Fóra <gyfora@apache.org> wrote:
> Hey!
> Now that we are implementing more and more applications for streaming that
> use iterations we realized a huge shortcoming of the current iteration api.
> Currently it only allows to feedback data of the same type to the iteration
> head.
> This makes sense because the operators are typed but makes it awkward if we
> indeed want to use a different feedback (such as a model syncing for
> machine learning applications). To do this developers need to use wrapper
> types and flags to distinguish the inputs.
> I propose to add the possibility to tread the original input of the
> iteration head operator and the feedback stream as a ConnectedDataStream so
> we can apply operators such as CoMap, CoFlatMap etc. This helps
> distinguishing the inputs and also allows different feedback types to be
> used. I believe this change is inevitable if we want to write elegant
> applications without unnecessary wrapper types.
> I made a PR <https://github.com/apache/flink/pull/870> already that
> introduces this functionality (it is a very small change in fact).
> Cheers,
> Gyula

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