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https://issues.apache.org/jira/browse/HADOOP-3140?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12584711#action_12584711
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Amar Kamat commented on HADOOP-3140:
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Arun, Two things
1) If the status is replayed by the TaskTracker, the JobTracker will take care
of that. The {{JobTracker.heartbeat()}} will simply discard it there and then.
2) If at all the status gets replayed (in {{JobInProgress.updateTaskStatus()}})
it will be taken care as follows
a) task t comes in as {{SUCCEEDED}} for a tip that is already completed.
b) It will be marked (locally) as {{KILLED}} and the tasks status will be
updated in the JT.
c) If at all the status is resent, it will be marked locally as {{KILLED}}. Now
the *change* in the status will result in as _false_ and nothing will happen.
The reason for marking the task as {{KILLED}} (locally) is to make sure that
the semantics of the trunk is retained. If the state is updated first and
later marked as {{KILLED}} then the task status will be temporarily marked as
{{SUCCEEDED}}.
> JobTracker should not try to promote a (map) task if it does not write to DFS
> at all
> ------------------------------------------------------------------------------------
>
> Key: HADOOP-3140
> URL: https://issues.apache.org/jira/browse/HADOOP-3140
> Project: Hadoop Core
> Issue Type: Bug
> Components: mapred
> Reporter: Runping Qi
> Assignee: Amar Kamat
> Fix For: 0.17.0
>
> Attachments: HADOOP-3140-v1.patch
>
>
> In most cases, map tasks do not write to dfs.
> Thus, when they complete, they should not be put into commit_pending queue at
> all.
> This will improve the task promotion significantly.
>
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