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From "Zheng Shao (JIRA)" <j...@apache.org>
Subject [jira] Commented: (MAPREDUCE-1129) Assign multiple Map and Reduce tasks in Fairscheduler
Date Thu, 22 Oct 2009 00:23:59 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-1129?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12768530#action_12768530
] 

Zheng Shao commented on MAPREDUCE-1129:
---------------------------------------

One simple idea is to change the interface of LoadManager:

From:

[code}
boolean LoadManager.canAssignMap(...)
boolean LoadManager.canAssignReduce(...)
{code}

To:

[code}
int LoadManager.canAssignMapCount(...)
int LoadManager.canAssignReduceCount(...)
{code}

The LoadManager returns the number of map(or reduce) tasks that can be assigned to this TaskTracker,
so we can assign multiple tasks in a single heartbeat.
The default implementation of the new functions can directly call the old functions to return
0 or 1, to provide backward compatibility with user-defined LoadManagers.


> Assign multiple Map and Reduce tasks in Fairscheduler
> -----------------------------------------------------
>
>                 Key: MAPREDUCE-1129
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-1129
>             Project: Hadoop Map/Reduce
>          Issue Type: Improvement
>          Components: contrib/fair-share
>    Affects Versions: 0.20.1
>            Reporter: Scott Chen
>
> In Hadoop-0.20, the period of heartbeat becomes much longer. 
> Fairscheduler assigns at most one Map and one Reduce task per heartbeat.
> This makes the cluster become very inefficient. Often time only half of the slots are
used.
> One idea is that we make Fairscheduler detect this situation (cluster under used) and
scheduler more tasks in a heartbeat.
> Thoughts?

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