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https://issues.apache.org/jira/browse/MAPREDUCE-1221?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12857405#action_12857405
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Arun C Murthy commented on MAPREDUCE-1221:
------------------------------------------
Scott, I had a question:
Comparing the following snippets in
src/java/org/apache/hadoop/mapred/TaskMemoryManagerThread.java
{noformat}
+ if (doCheckVirtualMemory() &&
+ isProcessTreeOverLimit(tid.toString(), currentMemUsage,
curMemUsageOfAgedProcesses, limit)) {
{noformat}
{noformat}
+ } else if (doCheckPhysicalMemory() && limitPhysical > 0 &&
+ isProcessTreeOverLimit(tid.toString(), currentRssMemUsage,
+ curRssMemUsageOfAgedProcesses, limitPhysical))
{
{noformat}
I don't understand why 'limitPhysical > 0' is necessary. If
'doCheckPhysicalMemory' returns true, shouldn't limitPhysical always be
positive? Please help me understand, thanks.
> 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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