download：破解 JavaScript 高级玩法

解决问题后的好奇

如果每个目录都会产生一个 Bucket，那如果运行一个流作业，岂不是迟早碰到雷同的问题。这么不言而喻的问题， 社区 的大神们必定早就想到了，好奇心驱使着我寻找答案——直到看到了这段代码：

public void commitUpToCheckpoint(final long checkpointId) throws IOException {
        final Iterator<Map.Entry<BucketID, Bucket<IN, BucketID>>> activeBucketIt =
                activeBuckets.entrySet().iterator();

        LOG.info("Subtask {} received completion notification for checkpoint with id={}.",
                subtaskIndex,
                checkpointId);

        while (activeBucketIt.hasNext()) {final Bucket<IN, BucketID> bucket = activeBucketIt.next().getValue();
            bucket.onSuccessfulCompletionOfCheckpoint(checkpointId);

            if (!bucket.isActive()) {
                // We've dealt with all the pending files and the writer for this bucket is not
                // currently open.
                // Therefore this bucket is currently inactive and we can remove it from our state.
                activeBucketIt.remove();
                notifyBucketInactive(bucket);
            }
        }
    }

做 Checkpoint 后的提交时，这里会依据 Bucket 是否处于沉闷状态来决定是否移除在内存中保护的数据结构。