[jira] [Created] (FLINK-9428) Allow operators to flush data on checkpoint pre-barrier

["Stephan Ewen (JIRA)" <ji...@apache.org>]

Stephan Ewen created FLINK-9428:
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             Summary: Allow operators to flush data on checkpoint pre-barrier
                 Key: FLINK-9428
                 URL: https://issues.apache.org/jira/browse/FLINK-9428
             Project: Flink
          Issue Type: New Feature
          Components: State Backends, Checkpointing
            Reporter: Stephan Ewen
            Assignee: Stephan Ewen
             Fix For: 1.6.0


Some operators maintain some small transient state that may be inefficient to checkpoint, especially when it would need to be checkpointed also in a re-scalable way.
An example are opportunistic pre-aggregation operators, which have small the pre-aggregation state that is frequently flushed downstream.

Rather that persisting that state in a checkpoint, it can make sense to flush the data downstream upon a checkpoint, to let it be part of the downstream operator's state.

This feature is sensitive, because flushing state has a clean implication on the downstream operator's checkpoint alignment. However, used with care, and with the new back-pressure-based checkpoint alignment, this feature can be very useful.

Because it is sensitive, I suggest to make this only an internal feature (accessible to operators) and NOT expose it in the public API at this point.



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