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From "Tsz Wo (Nicholas), SZE (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-1114) Reducing NameNode memory usage by an alternate hash table
Date Wed, 23 Jun 2010 17:17:55 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1114?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12881764#action_12881764
] 

Tsz Wo (Nicholas), SZE commented on HDFS-1114:
----------------------------------------------

> 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.

I used System.getProperty("sun.arch.data.model") in the patch.  See http://java.sun.com/docs/hotspot/HotSpotFAQ.html#64bit_detection

> 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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