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https://issues.apache.org/jira/browse/FLINK-3761?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15290885#comment-15290885
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ASF GitHub Bot commented on FLINK-3761:
---------------------------------------

Github user tillrohrmann commented on the pull request:

    https://github.com/apache/flink/pull/1988#issuecomment-220289629
  
    In order to support scaling for non-partitioned state, the next step could 
be the introduction of a kind of union state. The idea would be to aggregate 
the non-partitioned state of each subtask and then sending it to all subtasks 
upon recovery. Then every subtask can pick from the union state what it needs 
for its execution


> Introduce key group state backend
> ---------------------------------
>
>                 Key: FLINK-3761
>                 URL: https://issues.apache.org/jira/browse/FLINK-3761
>             Project: Flink
>          Issue Type: Sub-task
>          Components: state backends
>            Reporter: Till Rohrmann
>            Assignee: Till Rohrmann
>
> After an off-line discussion with [~aljoscha], we came to the conclusion that 
> it would be beneficial to reflect the differences between a keyed and a 
> non-keyed stream also in the state backends. A state backend which is used 
> for a keyed stream offers a value, list, folding and value state and has to 
> group its keys into key groups. 
> A state backend for non-keyed streams can only offer a union state to make it 
> work with dynamic scaling. A union state is a state which is broadcasted to 
> all tasks in case of a recovery. The state backends can then select what 
> information they need to recover from the whole state (formerly distributed).



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