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https://issues.apache.org/jira/browse/MAPREDUCE-2261?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12998903#comment-12998903
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Lianhui Wang commented on MAPREDUCE-2261:
-----------------------------------------
i agree with Devaraj K.
in the current version, the fair scheduler assign only one task int per hear
beat.
in the class FairScheduler we can see the following:
assignTasks(TaskTracker tracker){
for (Schedulable sched: scheds) {
Task task = taskType == TaskType.MAP ?
sched.assignTask(tts, currentTime, visitedForMap) :
sched.assignTask(tts, currentTime, visitedForReduce);
if (task != null) {
tasks.add(task);
break; // This break makes this loop assign only one task
}
}
}
if it assgin one task,the function will return.
> Fair Multiple Task Assignment Scheduler (Assigning multiple tasks per heart
> beat)
> ---------------------------------------------------------------------------------
>
> Key: MAPREDUCE-2261
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-2261
> Project: Hadoop Map/Reduce
> Issue Type: New Feature
> Affects Versions: 0.21.0
> Reporter: Devaraj K
>
> Functionality wise the Fair Multiple Task Assignment Scheduler behaves
> the same way except the assignment of Tasks. Instead of assigning a single
> Task per heartbeat, it checks for all the jobs if any local or non-local Task
> that can be launched.
> Fair Multiple Task Assignment Scheduler has the advantage of assigning
> multiple jobs per heart beat interval depending upon the slots available on
> the Task Tracker, by configuring the number of parallel tasks to be executed
> in a Task Tracker at any point of time. The advantages are as follows:
> a) Parallel Execution allows tasks be to submitted and processed in parallel
> independent of the status of other tasks.
> b) More number of tasks is assigned in a heartbeat interval and consequently
> multitasking capability increases.
> c) With multi task assignment, Task Tracker efficiency is increased.
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