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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 Thu, 15 Apr 2010 18:24:54 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-1221?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12857468#action_12857468
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Scott Chen commented on MAPREDUCE-1221:
---------------------------------------

Arun, Thanks for the review
bq. We shouldn't be using the TT.fConf to read config values each time, please save it and
re-use:
Good catch. I made some change. A member called reservedPhysicalMemoryOnTT is created to save
this value.

bq. I don't understand why 'limitPhysical > 0' is necessary. If 'doCheckPhysicalMemory'
returns true, shouldn't limitPhysical always be positive? Please help me understand, thanks.
You are right about this one. That check is redundant. If doCheckPhysicalMemory returns true,
it means the user has configured physical memory limit (should include per task limit) and
this value should not be negative.
The logic should be the same as the one in virtual memory limit. I have removed this redundant
check.

> 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, MAPREDUCE-1221-v5.txt
>
>
> 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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