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https://issues.apache.org/jira/browse/HADOOP-5964?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12721114#action_12721114
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Arun C Murthy commented on HADOOP-5964:
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Some notes about this patch:
# I've introduced a new org.apache.hadoop.mapred.server.jobtracker.TaskTracker
class to track all information about a given TaskTracker at the JobTracker such
as TaskTrackerStatus, reservations for high-ram jobs etc. I chose the new
package based on the proposals at HADOOP-398.
# I've changed the TaskScheduler.assignTasks api to use the newly introduced
rather than the tepid TaskTrackerStatus. Clearly other schedulers (ala
CapacityTaskScheduler) can start to take advantage of this as I've fixed them
appropriately in this patch.
# I've had to make some classes public (JobInProgress, TaskTrackerStatus) for
org.apache.hadoop.mapred.server.jobtracker.TaskTracker to work with appropriate
caveats in the javadocs etc.
> Fix the 'cluster drain' problem in the Capacity Scheduler wrt High RAM Jobs
> ---------------------------------------------------------------------------
>
> Key: HADOOP-5964
> URL: https://issues.apache.org/jira/browse/HADOOP-5964
> Project: Hadoop Core
> Issue Type: Bug
> Components: contrib/capacity-sched
> Affects Versions: 0.20.0
> Reporter: Arun C Murthy
> Assignee: Arun C Murthy
> Fix For: 0.21.0
>
> Attachments: HADOOP-5964_0_20090602.patch,
> HADOOP-5964_1_20090608.patch, HADOOP-5964_2_20090609.patch,
> HADOOP-5964_4_20090615.patch, HADOOP-5964_6_20090617.patch,
> HADOOP-5964_7_20090618.patch
>
>
> When a HighRAMJob turns up at the head of the queue, the current
> implementation of support for HighRAMJobs in the Capacity Scheduler has
> problem in that the scheduler stops assigning tasks to all TaskTrackers in
> the cluster until a HighRAMJob finds a suitable TaskTrackers for all its
> tasks.
> This causes a severe utilization problem since effectively no new tasks are
> allowed to run until the HighRAMJob (at the head of the queue) gets slots.
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