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https://issues.apache.org/jira/browse/MAPREDUCE-5863?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13982705#comment-13982705
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Mingzhe Hao commented on MAPREDUCE-5863:
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instead of being killed, the succeeded TA can also fail to change the task into
SCHEDULED state
> Killing task attempts while speculation is enabled can cause the job to fail
> ----------------------------------------------------------------------------
>
> Key: MAPREDUCE-5863
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-5863
> Project: Hadoop Map/Reduce
> Issue Type: Bug
> Affects Versions: 2.4.0
> Reporter: Mingzhe Hao
>
> There could be a race condition when a T_ADD_SPEC_ATTEMPT is being fired, the
> task gets succeeded and then killed by the client. In that case, the task
> state changes from SUCCEEDED to SCHEDULED, and then task gets a
> T_ADD_SPEC_ATTEMPT event, which is invalid for SCHEDULED state.
> 1. Task is running.
> 2. Speculator fires a T_ADD_SPEC_ATTEMPT
> 3. Before task receives T_ADD_SPEC_ATTEMPT, it succeeds
> 4. Succeeded TA receives TA_KILL from client. Now the task is at SCHEDULED
> state.
> 5. Task receives T_ADD_SPEC_ATTEMPT, since this is an unexpected event, the
> job fails.
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