Github user StefanRRichter commented on the pull request: https://github.com/apache/flink/commit/3400a87dce9940ac8da95c89ff9791ca6a687776#commitcomment-20654494 In flink-streaming-java/src/main/java/org/apache/flink/streaming/runtime/tasks/StreamTask.java: In flink-streaming-java/src/main/java/org/apache/flink/streaming/runtime/tasks/StreamTask.java on line 967: I am not sure about the guarantees we have in Akka and the underlying acknowledgement chain, but depending on how this works, is there a possibility that TM acknowledges a checkpoint, the JM receives the acknowledgment, marks the checkpoint as complete but the JM's message to the TM to acknowledge back is lost / timeout, leading to an exception in the TM's call. Would we have a data loss or does it work differently?
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