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https://issues.apache.org/jira/browse/HADOOP-4766?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12664085#action_12664085
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Amar Kamat commented on HADOOP-4766:
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@koji:
Using tasks as a unit of memory usage is very tricky. Ideally we would require
a memory model that can will help us derive memory requirements per
task/tip/job etc. Until we have a memory model in place I think its better to
go with the current solution as we only care about the overall memory used.
@Sharad:
Using soft references might be a better solution and might work well. But I
think it will be a major change in the framework and might be filed as an
improvement. Since this issue is more of a bug fix, I think we should go ahead
and use the current approach. Memory bottleneck with the JobTracker is
separately tracked in HADOOP-4974.
@Arun:
I am waiting for your input on the comments made
[here|https://issues.apache.org/jira/browse/HADOOP-4766?focusedCommentId=12663114#action_12663114].
> Hadoop performance degrades significantly as more and more jobs complete
> ------------------------------------------------------------------------
>
> Key: HADOOP-4766
> URL: https://issues.apache.org/jira/browse/HADOOP-4766
> Project: Hadoop Core
> Issue Type: Bug
> Components: mapred
> Affects Versions: 0.18.2, 0.19.0
> Reporter: Runping Qi
> Assignee: Amar Kamat
> Priority: Blocker
> Attachments: HADOOP-4766-v1.patch, HADOOP-4766-v2.10.patch,
> HADOOP-4766-v2.4.patch, HADOOP-4766-v2.6.patch, HADOOP-4766-v2.7-0.18.patch,
> HADOOP-4766-v2.7-0.19.patch, HADOOP-4766-v2.7.patch,
> HADOOP-4766-v2.8-0.18.patch, HADOOP-4766-v2.8-0.19.patch,
> HADOOP-4766-v2.8.patch, map_scheduling_rate.txt
>
>
> When I ran the gridmix 2 benchmark load on a fresh cluster of 500 nodes with
> hadoop trunk,
> the gridmix load, consisting of 202 map/reduce jobs of various sizes,
> completed in 32 minutes.
> Then I ran the same set of the jobs on the same cluster, yhey completed in 43
> minutes.
> When I ran them the third times, it took (almost) forever --- the job tracker
> became non-responsive.
> The job tracker's heap size was set to 2GB.
> The cluster is configured to keep up to 500 jobs in memory.
> The job tracker kept one cpu busy all the time. Look like it was due to GC.
> I believe the release 0.18/0.19 have the similar behavior.
> I believe 0.18 and 0.18 also have the similar behavior.
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