Hadoop 中JobClient 裏 submitJob(JobConf) 和 runJob(JobConf) 的區別

Hadoop提交 Job到JobTracker的時候，需要通過JobClient.runJob(JobConf) 或者 JobClient.submitJob(JobConf) 這兩個靜態方法來提交。但是這兩個方法，前者和後者是有區別的。查看API中的文檔解釋：

1）runJob

runJob

public static RunningJob runJob(JobConf job)
                         throws IOException

Utility that submits a job, then polls for progress until the job is complete.

Parameters:

job - the job configuration.

Throws:

IOException

2）submitJob

submitJob

public RunningJob submitJob(JobConf job)
                     throws FileNotFoundException,
                            InvalidJobConfException,
                            IOException

Submit a job to the MR system. This returns a handle to the RunningJob which can be used to track the running-job.

Parameters:

job - the job configuration.

Returns:

a handle to the RunningJob which can be used to track the running-job.

Throws:

FileNotFoundException

InvalidJobConfException

IOException

       可以看出，runJob是同步的，提交任務後要等待處理直到完成以後，纔會返回RunningJob的handle；而submitJob是異步的，會返回一個處理中的RuningJob的handle，然後等有資源的時候，纔會真正的去執行提交的任務。