flink checkpoint里面有一个概念，externalized checkpoints，这里externalized是什么意思？有没有对应的概念，可以叫做internal checkpoints？
即使我不调用enableExternalizedCheckpoints方法，但是当我在hdfs上指定一个检查点路径时，我认为我在外部持久化检查点，我能说我在做externalized checkpoints吗？
所以，我有点困惑。

/**
     * Enables checkpoints to be persisted externally.
     *
     * <p>Externalized checkpoints write their meta data out to persistent
     * storage and are <strong>not</strong> automatically cleaned up when
     * the owning job fails or is suspended (terminating with job status
     * {@link JobStatus#FAILED} or {@link JobStatus#SUSPENDED}). In this
     * case, you have to manually clean up the checkpoint state, both
     * the meta data and actual program state.
     *
     * <p>The {@link ExternalizedCheckpointCleanup} mode defines how an
     * externalized checkpoint should be cleaned up on job cancellation. If you
     * choose to retain externalized checkpoints on cancellation you have you
     * handle checkpoint clean up manually when you cancel the job as well
     * (terminating with job status {@link JobStatus#CANCELED}).
     *
     * <p>The target directory for externalized checkpoints is configured
     * via {@link org.apache.flink.configuration.CheckpointingOptions#CHECKPOINTS_DIRECTORY}.
     *
     * @param cleanupMode Externalized checkpoint cleanup behaviour.
     */
    @PublicEvolving
    public void enableExternalizedCheckpoints(ExternalizedCheckpointCleanup cleanupMode) {
        this.externalizedCheckpointCleanup = checkNotNull(cleanupMode);
    }