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https://issues.apache.org/jira/browse/HDFS-1114?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12879989#action_12879989
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Tsz Wo (Nicholas), SZE commented on HDFS-1114:
----------------------------------------------
Comparing memory footprint on a 32-bit VM over 1,000,000 elements
{noformat}
num #instances #bytes class name
----------------------------------------------
1: 1000040 24000960 java.util.HashMap$Entry
2: 1000000 24000000
org.apache.hadoop.hdfs.util.TestGSet$IntElement
3: 23 8390960 [Ljava.util.HashMap$Entry;
HashMap: 53.78 MB
num #instances #bytes class name
----------------------------------------------
1: 1000000 24000000
org.apache.hadoop.hdfs.util.TestGSet$IntElement
2: 1 4194320
[Lorg.apache.hadoop.hdfs.util.LightWeightGSet$LinkedElement;
LightWeightGSet: 26.89 MB
{noformat}
> 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: 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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