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https://issues.apache.org/jira/browse/FLINK-5601?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17886061#comment-17886061
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juntaozhang commented on FLINK-5601:
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[~danderson] ,thank you so much for letting me know the background
> Window operator does not checkpoint watermarks
> ----------------------------------------------
>
> Key: FLINK-5601
> URL: https://issues.apache.org/jira/browse/FLINK-5601
> Project: Flink
> Issue Type: Improvement
> Components: Runtime / Checkpointing
> Affects Versions: 1.5.0, 1.6.0, 1.7.0, 1.8.0, 1.9.0, 1.10.0, 1.11.0
> Reporter: Ufuk Celebi
> Priority: Not a Priority
> Labels: auto-deprioritized-critical, auto-deprioritized-major,
> auto-deprioritized-minor, auto-unassigned, pull-request-available
>
> 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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