This is the core interface for stateful transformation functions, meaning functions that maintain state across individual stream records.
Sources that implement this interface do not trigger checkpoints when receiving a trigger message from the checkpoint coordinator, but when their input data/events indicate that a checkpoint should be triggered.
|ListCheckpointed<T extends Serializable>||
This interface can be implemented by functions that want to store state in checkpoints and supports list-style state redistribution for cases when the parallelism of the transformation is changed.
This interface can be implemented by streaming functions that need to trigger a "global action" on the master (in the checkpoint coordinator) as part of every checkpoint and restore operation.
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