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From "Devaraj Das (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-2141) speculative execution start up condition based on completion time
Date Tue, 24 Feb 2009 10:50:02 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-2141?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12676242#action_12676242
] 

Devaraj Das commented on HADOOP-2141:
-------------------------------------

The field TaskInProgress.mostRecentStartTime is updated with the same value of execStartTime
each time (since execStartTime is updated only once in the life of the TIP). Did you mean
to do this?

bq. I am getting a little lost digging through the code trying to figure out where these variables
would need to be decremented at
They should be decremented in TIP.incompleteSubTask and TIP.completedTask (basically, places
where activeTasks.remove) is done. The decrement should happen if activeTasks.size for the
TIP is >1. Makes sense?

bq. I can't find the TaskCommitThread that it references
Yes this comment shouldn't be there. TaskCommitThread used to be there at one point..

bq. there would be a possibility of speculating a task that has already completed.
Couldn't it be checked whether TIP.isComplete() returns true before launching a speculative
attempt?

> speculative execution start up condition based on completion time
> -----------------------------------------------------------------
>
>                 Key: HADOOP-2141
>                 URL: https://issues.apache.org/jira/browse/HADOOP-2141
>             Project: Hadoop Core
>          Issue Type: Improvement
>          Components: mapred
>    Affects Versions: 0.19.0
>            Reporter: Koji Noguchi
>            Assignee: Andy Konwinski
>         Attachments: 2141.patch, HADOOP-2141-v2.patch, HADOOP-2141-v3.patch, HADOOP-2141-v4.patch,
HADOOP-2141-v5.patch, HADOOP-2141.patch
>
>
> We had one job with speculative execution hang.
> 4 reduce tasks were stuck with 95% completion because of a bad disk. 
> Devaraj pointed out 
> bq . One of the conditions that must be met for launching a speculative instance of a
task is that it must be at least 20% behind the average progress, and this is not true here.
> It would be nice if speculative execution also starts up when tasks stop making progress.
> Devaraj suggested 
> bq. Maybe, we should introduce a condition for average completion time for tasks in the
speculative execution check. 

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