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https://issues.apache.org/jira/browse/HDFS-1114?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12879975#action_12879975
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Tsz Wo (Nicholas), SZE commented on HDFS-1114:
----------------------------------------------
Ran some benchmarks. When the modulus is large, which means that number of
collisions is small, LightWeightGSet is much better than GSetByHashMap.
|| datasize || modulus || GSetByHashMap|| LightWeightGSet||
| 65536 | 1025 | 219 | 234|
| 65536 | 1048577 | 516 | 296|
| 65536 | 1073741825 | 500 | 281|
| 262144 | 1025 | 1422 | 1531|
| 262144 | 1048577 | 3078 | 2156|
| 262144 | 1073741825 | 3094 | 2281|
| 1048576 | 1025 | 7172 | 7313|
| 1048576 | 1048577 | 13531 | 9844|
| 1048576 | 1073741825 | 14485 | 10718|
> 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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