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From "Arun C Murthy (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-657) Free temporary space should be modelled better
Date Thu, 09 Nov 2006 17:00:39 GMT
    [ http://issues.apache.org/jira/browse/HADOOP-657?page=comments#action_12448519 ] 
Arun C Murthy commented on HADOOP-657:

Current flow relevant to this discussion:

TaskTracker.offerService() -> TaskTracker.checkForNewTasks() -> if (TaskTracker.enoughFreeSpace())
then poll/startNewTask

We could put the above checks (infact we can do better by checking if we have assigned fileSplit's
size * conf.getFloat("map.output.growth.factor", 1.0)) in TaskTracker.enoughFreeSpace()...

... alternatively we could make '(sum over running tasks of (1.0 - done) * allocation)' part
of TaskTrackerStatus i.e. a 'availableDiskSpace' member, check to ensure that 'sufficient'
free space is available on the tasktracker before assigning it the task itself in JobInProgress.findNewTask
- this ensures that a task isn't allocated in the first place to a tasktracker if it can't
handle it.

What do you guys think? Am I missing out on something which prevents option #2 from working?

> Free temporary space should be modelled better
> ----------------------------------------------
>                 Key: HADOOP-657
>                 URL: http://issues.apache.org/jira/browse/HADOOP-657
>             Project: Hadoop
>          Issue Type: Improvement
>          Components: mapred
>    Affects Versions: 0.7.2
>            Reporter: Owen O'Malley
>         Assigned To: Arun C Murthy
> Currently, there is a configurable size that must be free for a task tracker to accept
a new task. However, that isn't a very good model of what the task is likely to take. I'd
like to propose:
> Map tasks:  totalInputSize * conf.getFloat("map.output.growth.factor", 1.0) / numMaps
> Reduce tasks: totalInputSize * 2 * conf.getFloat("map.output.growth.factor", 1.0) / numReduces
> where totalInputSize is the size of all the maps inputs for the given job.
> To start a new task, 
>   newTaskAllocation + (sum over running tasks of (1.0 - done) * allocation) >= 
>        free disk * conf.getFloat("mapred.max.scratch.allocation", 0.90);
> So in English, we will model the expected sizes of tasks and only task tasks that should
leave us a 10% margin. With:
> map.output.growth.factor -- the relative size of the transient data relative to the map
> mapred.max.scratch.allocation -- the maximum amount of our disk we want to allocate to

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