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From "Yi Liu (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-8988) Use LightWeightHashSet instead of LightWeightLinkedSet in BlockManager#excessReplicateMap
Date Mon, 12 Oct 2015 07:12:05 GMT

    [ https://issues.apache.org/jira/browse/HDFS-8988?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14952724#comment-14952724
] 

Yi Liu commented on HDFS-8988:
------------------------------

Thanks [~umamaheswararao] for the review, the test failure are not related and can pass locally.
I will fix the checkstyle about one line is longer than 80 characters while committing.

> Use LightWeightHashSet instead of LightWeightLinkedSet in BlockManager#excessReplicateMap
> -----------------------------------------------------------------------------------------
>
>                 Key: HDFS-8988
>                 URL: https://issues.apache.org/jira/browse/HDFS-8988
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>            Reporter: Yi Liu
>            Assignee: Yi Liu
>         Attachments: HDFS-8988.001.patch, HDFS-8988.002.patch
>
>
> {code}
> public final Map<String, LightWeightLinkedSet<Block>> excessReplicateMap
= new HashMap<>();
> {code}
> {{LightWeightLinkedSet}} extends {{LightWeightHashSet}} and in addition it stores elements
in double linked list to ensure ordered traversal. So it requires more memory for each entry
(2 references = 8 + 8 bytes = 16 bytes, assume 64-bits system/JVM).  
> I have traversed the source code, and we don't need ordered traversal for excess replicated
blocks, so could use  {{LightWeightHashSet}} to save memory.



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