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https://issues.apache.org/jira/browse/MAPREDUCE-6622?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15159483#comment-15159483
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Ray Chiang commented on MAPREDUCE-6622:
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In order to minimize impact, I didn't really do any real rewrite of the
internals of CachedHistoryStorage. I just swapped in the cache access.
Here's my understanding of getFullJob():
- It's using the HistoryFileManager "fileInfo" as a proxy to determine whether
the job exists.
- If the job exists, it then checks the cache via loadedJobCache#getIfPresent()
- If the job isn't in the cache, it loads the file into memory
- If job history file has been deleted, getFullJob returns null
> 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, MAPREDUCE-6622.005.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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