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https://issues.apache.org/jira/browse/HADOOP-4766?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12663580#action_12663580
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Sharad Agarwal commented on HADOOP-4766:
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One altogether different approach could be to use Soft references which are
good for memory sensitive caches and this case is pretty much the same.
This way we won't need the retire thread and any parameter for defining max
jobs/tasks in history. The jvm would take care of it on its own.
The way it could work is when job finishes, the job handle is removed from the
datastructure and instead new SoftReference(job) handle is put back. When jvm
is short of memory, it will clear all the soft references. In
JobInProgress#finalize() we can do the clean up work corresponding to that job
like clearing other references and doing removeJobTasks().
> 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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