[jira] [Resolved] (MAPREDUCE-402) TaskTracker doesnt recheck job tracker version on reconnect

["Allen Wittenauer (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/MAPREDUCE-402?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Allen Wittenauer resolved MAPREDUCE-402.
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    Resolution: Incomplete

Closing this as stale.

> TaskTracker doesnt recheck job tracker version on reconnect
> -----------------------------------------------------------
>
>                 Key: MAPREDUCE-402
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-402
>             Project: Hadoop Map/Reduce
>          Issue Type: Bug
>            Reporter: Steve Loughran
>            Priority: Minor
>
> This isnt anything I have a test for/encountered, just something I noticed when reviewing TaskTracker.
> 1. TaskTracker sets a justStarted flag to true when starting up
> 2. One way it uses this flag is to check job tracker versions -the version is only checked when justStarted==true, which is reset after the check.
> 3. If a JobTracker is unreachable, then the TaskTracker sleeps for 5 seconds and then continues
> There is a risk, therefore, that if the job tracker goes down, a different version might come back up, and the Task Tracker will not notice until it makes an incompatible IPC call.
> This is a pretty unlikely scenario; you've got to kill the job tracker and bring up a different versioned one in 5 seconds. And the consequence of IPC incompatiblity will be a lost task, regardless of whether this happens early or later in the process. I'm not sure it's worth fixing. 



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