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 [[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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