[jira] [Commented] (FLINK-5601) Window operator does not checkpoint watermarks

["Jiayi Liao (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/FLINK-5601?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16628650#comment-16628650 ] 

Jiayi Liao commented on FLINK-5601:
-----------------------------------

I think I can do this. We have the same problem on our production business. 

> 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
>            Priority: Critical
>             Fix For: 1.7.0
>
>
> During release testing [~stefanrichter83@gmail.com] 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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