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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 Fri, 30 Apr 2010 08:34:58 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1114?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12862583#action_12862583
] 

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

I believe we can save from 24 to 40 bytes per entry. It depends on the chosen implementation
(will give more details later).

In a large clusters, there are ~60m blocks. Then, we may save from 1.5GB to 2.5GB NN memory.

> 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
>
> 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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