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From "Karthik Kambatla (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MAPREDUCE-6622) Add capability to set JHS job cache to a task-based limit
Date Tue, 23 Feb 2016 07:14:18 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-6622?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15158438#comment-15158438
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Karthik Kambatla commented on MAPREDUCE-6622:
---------------------------------------------

Comments on the latest patch:
# Unused variable {{cleanupThread}} left over from previous iterations.
# The description for loadedjobs.cache.size config says it is ignored if loadedtasks.cache.size
is set. A default value of -1 actually means it is set. I like the previous approach of not
setting it at all. 
# Also, when reading the value for loadedtasks.cache.size, don't we want to enforce a minimum
value for it? May be, 1? 
# I am not sure I understand how entries are loaded into the cache. The CacheBuilder calls
getFullJob, but the latter checks if the entry is present in the cache? If I understand it
right, the public getFullJob() should just call {{loadedJobCache.get(jobID)}}. The CacheLoader
should call a private method {{loadJob(jobID)}}. The current contents of {{getFullJob}} -
get fileInfo etc. - should move to loadJob. 

> 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,
MAPREDUCE-6622.004.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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