Github user StephanEwen commented on the issue: https://github.com/apache/flink/pull/1668 @senorcarbone I agree, let's fix the multiple checkpoints issue and do the rest in FLIP-15 The other operators have a pretty simply way of doing this: - for synchronous checkpointed operators, no need to do anything, the synchronous part of one checkpoint is over when the next starts (because it is synchronous ;-)) - for asynchronously checkpointed state, the state backend needs to be able to hold multiple snapshots, which are saved by multiple background threads - none of the operators deal with in-flight data, which makes their job easy Dealing with in-flight data probably means that you need to open a ListState for each checkpoint that arrives and add the feed back values to each state, until that particular checkpoints barrier comes back through the feedback channel. I think that should be sufficient.
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