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http://issues.apache.org/jira/browse/HADOOP-657?page=comments#action_12448519 ]
Arun C Murthy commented on HADOOP-657:
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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 inputs
> mapred.max.scratch.allocation -- the maximum amount of our disk we want to
> allocate to tasks.
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