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https://issues.apache.org/jira/browse/FLINK-5601?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16629956#comment-16629956
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Aljoscha Krettek commented on FLINK-5601:
-----------------------------------------
This is not a trivial issue. Before writing any code, please spell out how you
want to approach this.
> Window operator does not checkpoint watermarks
> ----------------------------------------------
>
> Key: FLINK-5601
> URL: https://issues.apache.org/jira/browse/FLINK-5601
> Project: Flink
> Issue Type: Improvement
> Components: State Backends, Checkpointing
> Affects Versions: 1.5.0, 1.6.0
> Reporter: Ufuk Celebi
> Assignee: Jiayi Liao
> Priority: Critical
> Fix For: 1.7.0
>
>
> During release testing [[email protected]] and I noticed that
> watermarks are not checkpointed in the window operator.
> This can lead to non determinism when restoring checkpoints. I was running an
> adjusted {{SessionWindowITCase}} via Kafka for testing migration and
> rescaling and ran into failures, because the data generator required
> determinisitic behaviour.
> What happened was that on restore it could happen that late elements were not
> dropped, because the watermarks needed to be re-established after restore
> first.
> [~aljoscha] Do you know whether there is a special reason for explicitly not
> checkpointing watermarks?
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