如下 Exception in thread "main" java.lang.UnsupportedOperationException: Checkpointing is currently not supported by default for iterative jobs, as we cannot guarantee exactly once semantics. State checkpoints happen normally, but records in-transit during the snapshot will be lost upon failure. The user can force enable state checkpoints with the reduced guarantees by calling: env.enableCheckpointing(interval,true) 。 Flink当前针对IterativeJob不支持检查点，但可以强制开启。
我需要知道的是，强制开启后，对状态影响多大？无法保证没问题的是哪部分状态，还是对普通流算子的状态也会受到影响呢？ or影响只是iterative的feedback部分？还是什么部分？
