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https://issues.apache.org/jira/browse/HIVE-12310?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14993184#comment-14993184
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Thejas M Nair commented on HIVE-12310:
--------------------------------------
+1
> Update memory estimation login in TopNHash
> ------------------------------------------
>
> Key: HIVE-12310
> URL: https://issues.apache.org/jira/browse/HIVE-12310
> Project: Hive
> Issue Type: Bug
> Components: Query Processor
> Reporter: Thejas M Nair
> Assignee: Hari Sankar Sivarama Subramaniyan
> Attachments: HIVE-12310.1.patch
>
>
> HIVE-12084 changes TopNHash to use Runtime.getRuntime().freeMemory() for
> finding available memory.
> However, it does not give the all the memory it could use, it ignores
> unallocated memory. This is because the heap size of jvm grows up to max heap
> size (-Xmx) as per it needs. totalMemory() gives total heap space it has
> allocated, and freeMemory() is the free memory within that.
> See http://i.stack.imgur.com/GjuwM.png and
> http://stackoverflow.com/questions/3571203/what-is-the-exact-meaning-of-runtime-getruntime-totalmemory-and-freememory
> .
> So instead of using Runtime.getRuntime().freeMemory() , I think it should use
> maxMemory() - totalMemory() + freeMemory()
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