答复：UpdateTaskExecutionState during JobManager failover

[wangzhijiang999 <wa...@aliyun.com>]

Hi Stephan,
 Thank you for detail explaination.  As you said, my opition is to keep task still running druing jobmanager failover, even though sending update status failed.
For the first reason you mentioned, if i understand correctly, the key issue is status out of sync between taskmanager and jobmanager. For example, when the jobmanager failover, the task is at CREATED status . When the task status transition to RUNNING, the updateStatus message can not be received because of jobmanager failover, then the taskmanager will retry sending the message to jobmanager until success. When the jobmanager recovers, the previous status of task is still CREATED in jobmanager view, and the task status maybe actually transition to FINISHED in taskmanager view. The key problem is that when the jobmanager received the FINISHED earlier than the RUNNING message, it will reject the FINISHED message.  If the task maintain a queue for sending message during jobmanager failover in order to confirm that the messages will be received in sequence at jobmanager when recover, that means the RUNNING status message must be arrived before FINISHED status message, are there any problems?
For the second reason you mentioned,  i am not very clear of the machenism of filtering the critical message by leaderSessionID, would you extend it in detail? 
I am trying to improve process of jobmanager and taskmanager failover, thank you for your help!
Zhijiang Wang