TaskTracker doesnt recheck job tracker version on reconnect
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Key: HADOOP-3880
URL: https://issues.apache.org/jira/browse/HADOOP-3880
Project: Hadoop Core
Issue Type: Bug
Components: mapred
Affects Versions: 0.19.0
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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