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From "Charles Lamb (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-6658) Namenode memory optimization - Block replicas list
Date Wed, 11 Mar 2015 21:43:38 GMT

    [ https://issues.apache.org/jira/browse/HDFS-6658?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14357672#comment-14357672
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Charles Lamb commented on HDFS-6658:
------------------------------------

Hi [~daryn],

Colin and I read over the design doc. I confess that I still need to read over the patch,
but I will do that. Do you think it will be possible to create a safe mode to run this in
so that inconsistencies can be detected? I'm also wondering what the field widths are, but
I can find those when I read the patch.



> Namenode memory optimization - Block replicas list 
> ---------------------------------------------------
>
>                 Key: HDFS-6658
>                 URL: https://issues.apache.org/jira/browse/HDFS-6658
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: namenode
>    Affects Versions: 2.4.1
>            Reporter: Amir Langer
>            Assignee: Daryn Sharp
>         Attachments: BlockListOptimizationComparison.xlsx, BlocksMap redesign.pdf, HDFS-6658.patch,
HDFS-6658.patch, HDFS-6658.patch, Namenode Memory Optimizations - Block replicas list.docx,
New primative indexes.jpg, Old triplets.jpg
>
>
> Part of the memory consumed by every BlockInfo object in the Namenode is a linked list
of block references for every DatanodeStorageInfo (called "triplets"). 
> We propose to change the way we store the list in memory. 
> Using primitive integer indexes instead of object references will reduce the memory needed
for every block replica (when compressed oops is disabled) and in our new design the list
overhead will be per DatanodeStorageInfo and not per block replica.
> see attached design doc. for details and evaluation results.



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