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Date: Wed, 2 Apr 2008 11:31:25 -0700 (PDT)
From: "Amar Kamat (JIRA)" <jira@apache.org>
To: core-dev@hadoop.apache.org
Subject: [jira] Commented: (HADOOP-3140) JobTracker should not try to
 promote a (map) task if it does not write to DFS at all
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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 ] 

Amar Kamat commented on HADOOP-3140:
------------------------------------

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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