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https://issues.apache.org/jira/browse/MAPREDUCE-7277?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17089095#comment-17089095
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Jonathan Turner Eagles commented on MAPREDUCE-7277:
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!IndexCacheActualSize.png!
Analysis shows that occasionally items were removed when spill records were
under construction, giving them an effective size of 0 upon removal. As proper
barriers were not in place to prevent removal while under construction, after
the item was removed from the cache, it would finish construction adding its
full size to the totalMemoryUsed bookkeeping variable, causing the discrepancy
between totalMemoryUsed and the contents of the cache.
> IndexCache totalMemoryUsed differs from cache contents.
> -------------------------------------------------------
>
> Key: MAPREDUCE-7277
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-7277
> Project: Hadoop Map/Reduce
> Issue Type: Improvement
> Reporter: Jonathan Turner Eagles
> Assignee: Jonathan Turner Eagles
> Priority: Major
> Attachments: IndexCacheActualSize.png
>
>
> It was observed recently in a nodemanager OOM that the memory was filled with
> SpillRecords. However, the IndexCache was only 15% full (1.5MB used on a 10MB
> configured cache size). In particular was noted that the booking variable
> totalMemoryUsed, was out of sync with the contents of the cache showing 96%
> full, thereby drastically reducing the effectiveness of the cache.
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