With Async checkpointing the checkpoint callback in CheckpointPoint listener is called for a previous window, that is, beginWindow (x) -> endWindow(x) -> checkpointed (x-1 )
This feature was newly introduced. With synchronous checkpointing, the behavior was always beginWindow(x) -> endWindow(x) -> checkpointed (x) A lot of operators were written before asynchronous checkpointing was introduced and few of them can rely on the sequencing guaranteed by synchronous checkpointing. So why was Async Checkpointed made default? With how Async checkpoint is today, the complexity to handle transient state in checkpointed callback falls on every operator. For eg, lets say earlier I had a transient map which I cleared every time the checkpointed was called, with async checkpointing this simple task will be a lot more complicated. I think Async checkpointing broke the semantics of operator callbacks and should NOT be the default.
