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From "Scott Chen (JIRA)" <j...@apache.org>
Subject [jira] Commented: (MAPREDUCE-1221) Kill tasks on a node if the free physical memory on that machine falls below a configured threshold
Date Wed, 17 Mar 2010 22:05:30 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-1221?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12846613#action_12846613
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Scott Chen commented on MAPREDUCE-1221:
---------------------------------------

The definitions of the parameters in the previous comment are not very clear.
Here are the definitions.

*mapreduce.tasktracker.reserved.physicalmemory.mb*
Specify how much memory on the TT that will not be used by tasks.
For example if we configure this to be 2G and we have 16G of memory.
The tasks only allow to use 14G of memory. If the limit is exceeded, TT will kill the task
consumes the most amount of memory.
We use reserved memory instead of total memory because there may be cases that we have nonuniform
cluster.

*mapreduce.map.memory.physical.mb*
Memory limit for one mapper. If the mapper uses more memory that this, it will fail.

*mapreduce.reduce.memory.physical.mb*
Memory limit for one reducer. If the reducer uses more memory that this, it will fail.

> Kill tasks on a node if the free physical memory on that machine falls below a configured
threshold
> ---------------------------------------------------------------------------------------------------
>
>                 Key: MAPREDUCE-1221
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-1221
>             Project: Hadoop Map/Reduce
>          Issue Type: Improvement
>          Components: tasktracker
>    Affects Versions: 0.22.0
>            Reporter: dhruba borthakur
>            Assignee: Scott Chen
>             Fix For: 0.22.0
>
>         Attachments: MAPREDUCE-1221-v1.patch, MAPREDUCE-1221-v2.patch, MAPREDUCE-1221-v3.patch,
MAPREDUCE-1221-v4.patch
>
>
> The TaskTracker currently supports killing tasks if the virtual memory of a task exceeds
a set of configured thresholds. I would like to extend this feature to enable killing tasks
if the physical memory used by that task exceeds a certain threshold.
> On a certain operating system (guess?), if user space processes start using lots of memory,
the machine hangs and dies quickly. This means that we would like to prevent map-reduce jobs
from triggering this condition. From my understanding, the killing-based-on-virtual-memory-limits
(HADOOP-5883) were designed to address this problem. This works well when most map-reduce
jobs are Java jobs and have well-defined -Xmx parameters that specify the max virtual memory
for each task. On the other hand, if each task forks off mappers/reducers written in other
languages (python/php, etc), the total virtual memory usage of the process-subtree varies
greatly. In these cases, it is better to use kill-tasks-using-physical-memory-limits.

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