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

["Ufuk Celebi (JIRA)" <ji...@apache.org>]

Ufuk Celebi created FLINK-5601:
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             Summary: 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
            Reporter: Ufuk Celebi


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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