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https://issues.apache.org/jira/browse/HADOOP-4766?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12653192#action_12653192
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Runping Qi commented on HADOOP-4766:
------------------------------------


After setting the heapsize of the job tracker to 3GB, the situation becomes 
even worse --- the first set of gridmix 2 jobs did not finish in 4+ hours.

Something  wrong badly
.


> 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
>
> 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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