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From "eric baldeschwieler (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-2014) Job Tracker should prefer input-splits from overloaded racks
Date Thu, 14 Feb 2008 07:09:07 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-2014?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12568822#action_12568822
] 

eric baldeschwieler commented on HADOOP-2014:
---------------------------------------------

Sorry amar, maybe I don't follow.  Seems complicated.  We can implement and load test a few
strategies using gridmix.

Owen, we should pick tasks on each node and each rack using the same metric (split load) as
well.  All lists should be sorted by it?

Rather than having another list to maintain, we could perhaps just keep the rack lists (and
the node lists recursively) in heaps perhaps?  The heap is ordered by split load and allows
you to quickly choose the rack with the task with the highest split load.  Less to maintain
that way perhaps.




> Job Tracker should prefer input-splits from overloaded racks
> ------------------------------------------------------------
>
>                 Key: HADOOP-2014
>                 URL: https://issues.apache.org/jira/browse/HADOOP-2014
>             Project: Hadoop Core
>          Issue Type: Bug
>          Components: mapred
>            Reporter: Runping Qi
>            Assignee: Devaraj Das
>
> Currently, when the Job Tracker assigns a mapper task to a task tracker and there is
no local split to the task tracker, the
> job tracker will find the first runable task in the mast task list  and assign the task
to the task tracker.
> The split for the task is not local to the task tracker, of course. However, the split
may be local to other task trackers.
> Assigning the that task, to that task tracker may decrease the potential number of mapper
attempts with data locality.
> The desired behavior in this situation is to choose a task whose split is not local to
any  task tracker. 
> Resort to the current behavior only if no such task is found.
> In general, it will be useful to know the number of task trackers to which each split
is local.
> To assign a task to a task tracker, the job tracker should first  try to pick a task
that is local to the task tracker  and that has minimal number of task trackers to which it
is local. If no task is local to the task tracker, the job tracker should  try to pick a task
that has minimal number of task trackers to which it is local. 
> It is worthwhile to instrument the job tracker code to report the number of splits that
are local to some task trackers.
> That should be the maximum number of tasks with data locality. By comparing that number
with the the actual number of 
> data local mappers launched, we can know the effectiveness of the job tracker scheduling.
> When we introduce rack locality, we should apply the same principle.

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