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From "eric baldeschwieler (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-2141) speculative execution start up condition based on completion time
Date Mon, 27 Apr 2009 17:18:30 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-2141?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12703224#action_12703224
] 

eric baldeschwieler commented on HADOOP-2141:
---------------------------------------------

Can't you use the the task dispatch time from the JT as the base time to estimate progress?
 That would be consistent and a lot simpler than push responsibility to the TT.

The assertion that it is ok to run a speculative remotely is a little worrisome.  It seems
to me we should try to run them locally if possible.  After all, we might be running speculative
execution exactly because a task is slow due to networking issues...  I'd like to see this
tested.  Another issue is that the disk the source data is on may be overloaded or slow. 
So a preference to run local to another copy of the data be optimal for maps...

Seems like a rich area for further research once this first patch is in.  Andy, Devaraj -
Let's coordinate the validation of this patch on Y! resource.  We have some good test cases
from the terasort contest.

> 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: 0.21.0
>            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-v6.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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