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https://issues.apache.org/jira/browse/HDFS-1114?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12880423#action_12880423
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Scott Carey commented on HDFS-1114:
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bq. This is a good point. Is there a way to determine if UseCompressedOops is
set in runtime?
Well, there is ManagementFactory.getRuntimeMXBean().getInputArguments(), but
later versions of Java are going to be making +UseCompressedOops the default.
There is also a way to check if the VM is 64 bit or 32 bit, either its out of
ManagementFactory or one of the system properties. Digging around I don't see
it, but I have used it before. I think it is vendor specific though.
> Reducing NameNode memory usage by an alternate hash table
> ---------------------------------------------------------
>
> Key: HDFS-1114
> URL: https://issues.apache.org/jira/browse/HDFS-1114
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: name-node
> Reporter: Tsz Wo (Nicholas), SZE
> Assignee: Tsz Wo (Nicholas), SZE
> Fix For: 0.22.0
>
> Attachments: benchmark20100618.patch, GSet20100525.pdf,
> gset20100608.pdf, h1114_20100607.patch, h1114_20100614b.patch,
> h1114_20100615.patch, h1114_20100616b.patch, h1114_20100617.patch,
> h1114_20100617b.patch
>
>
> NameNode uses a java.util.HashMap to store BlockInfo objects. When there are
> many blocks in HDFS, this map uses a lot of memory in the NameNode. We may
> optimize the memory usage by a light weight hash table implementation.
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