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https://issues.apache.org/jira/browse/MAPREDUCE-2261?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12999238#comment-12999238
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Todd Lipcon commented on MAPREDUCE-2261:
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MAPREDUCE-706 was a poorly named JIRA. It actually rewrote much of the fair
scheduler, including adding this feature. In trunk, look at the usage of the
mapAssignCap and reduceAssignCap variables. You'll see that assignTasks loops
until the specified number of tasks have been assigned or the load manager
indicates that no more can be assigned.
> 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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