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https://issues.apache.org/jira/browse/MAPREDUCE-771?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Hemanth Yamijala updated MAPREDUCE-771:
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Attachment: MAPREDUCE-771.patch
Attached patch fixes the issue in scheduling of setup and cleanup tasks. The
fix is to use TaskTrackerStatus.countOccupied{Map|Reduce}Slots to get the right
number of slots to account to.
In order to test this in unit test style, I've marked the method
JobTracker.getSetupAndCleanupTasks as package private. Introduced a new test
class TestSetupTaskScheduling to test these conditions. Verified without the
code fix the corresponding tests fail.
Arun and I felt that changing the usage in other schedulers from using slots to
tasks is probably best left to a different jira as the impact needs to be more
carefully studied, and this is a simple bug that only affects setup and cleanup
tasks in the case of capacity scheduler right now.
I plan to run a real cluster test tomorrow manually to ensure things work fine
still. But I would appreciate a review in the meantime.
> Setup and cleanup tasks remain in UNASSIGNED state for a long time on
> tasktrackers with long running high RAM tasks
> -------------------------------------------------------------------------------------------------------------------
>
> Key: MAPREDUCE-771
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-771
> Project: Hadoop Map/Reduce
> Issue Type: Bug
> Components: jobtracker
> Affects Versions: 0.21.0
> Reporter: Hemanth Yamijala
> Fix For: 0.21.0
>
> Attachments: MAPREDUCE-771.patch
>
>
> When a high RAM job's task is scheduled on a tasktracker, the number of slots
> it occupies will be more than one. If enough such tasks are scheduled, there
> can come a situation when there are no more slots free on the node but the
> number of tasks running is less than the number of slots. The jobtracker
> currently schedules a setup or cleanup task based on how many tasks are
> running on the system, rather than slots. As a result of this, it can
> schedule a setup or cleanup task on a tasktracker without any free slots. If
> the high RAM job's tasks are long running, this will significantly delay the
> running of the setup or cleanup task, and thus the entire job.
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