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From "Ray Chiang (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (MAPREDUCE-6622) Add capability to set JHS job cache to a task-based limit
Date Mon, 22 Feb 2016 21:33:18 GMT

     [ https://issues.apache.org/jira/browse/MAPREDUCE-6622?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Ray Chiang updated MAPREDUCE-6622:
----------------------------------
    Release Note: 
Two recommendations for the mapreduce.jobhistory.loadedtasks.cache.size property:
1) For every 100k of cache size, set the heap size of the Job History Server to 1.2GB.  For
example, mapreduce.jobhistory.loadedtasks.cache.size=500, heap size=6GB.
2) Make sure that the cache size is larger than the number of tasks required for the largest
job run on the cluster.  It might be a good idea to set the value slightly higher (say, 20%)
in order to allow for job size growth.

> Add capability to set JHS job cache to a task-based limit
> ---------------------------------------------------------
>
>                 Key: MAPREDUCE-6622
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-6622
>             Project: Hadoop Map/Reduce
>          Issue Type: Improvement
>          Components: jobhistoryserver
>    Affects Versions: 2.7.2
>            Reporter: Ray Chiang
>            Assignee: Ray Chiang
>              Labels: supportability
>         Attachments: MAPREDUCE-6622.001.patch, MAPREDUCE-6622.002.patch, MAPREDUCE-6622.003.patch
>
>
> When setting the property mapreduce.jobhistory.loadedjobs.cache.size the jobs can be
of varying size.  This is generally not a problem when the jobs sizes are uniform or small,
but when the job sizes can be very large (say greater than 250k tasks), then the JHS heap
size can grow tremendously.
> In cases, where multiple jobs are very large, then the JHS can lock up and spend all
its time in GC.  However, since the cache is holding on to all the jobs, not much heap space
can be freed up.
> By setting a property that sets a cap on the number of tasks allowed in the cache and
since the total number of tasks loaded is directly proportional to the amount of heap used,
this should help prevent the JHS from locking up.



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