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https://issues.apache.org/jira/browse/FLINK-2631?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14738536#comment-14738536
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ASF GitHub Bot commented on FLINK-2631:
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Github user fhueske commented on the pull request:
https://github.com/apache/flink/pull/1101#issuecomment-139194304
LGTM, will merge
> StreamFold operator does not respect returns type and stores non serializable
> values
> ------------------------------------------------------------------------------------
>
> Key: FLINK-2631
> URL: https://issues.apache.org/jira/browse/FLINK-2631
> Project: Flink
> Issue Type: Bug
> Reporter: Till Rohrmann
> Assignee: Till Rohrmann
>
> The {{StreamFold}} operator stores the initial value of the fold operation
> for the task deployment. This value does not necessarily have to be
> serializable. Thus, using the fold operation with a non-serializable initial
> value will fail the job.
> Moreover, the {{StreamFold}} operator needs to know the output type in order
> to create a {{TypeSerializer}}. For {{StreamGraphs}} where the output type is
> not know when the operator is created, as it is the case for the Scala
> DataStream API which directly sets the output type after creating the
> operator via the {{returns}} method, this approach will fail. The reason is
> that the {{StreamFold}} operator does receive the type information set by the
> {{returns}} method. Therefore, the job will fail at runtime because the
> operator tries to create a serializer from a {{MissingTypeInformation}}.
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