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From "Colin Patrick McCabe (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-6658) Namenode memory optimization - Block replicas list
Date Sat, 21 Mar 2015 04:33:39 GMT

    [ https://issues.apache.org/jira/browse/HDFS-6658?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14372508#comment-14372508
] 

Colin Patrick McCabe commented on HDFS-6658:
--------------------------------------------

Daryn, I apologize for not being more responsive on this.  I've been dealing with some burning
fires around here and haven't had time to look at it more.  It would be nice if this could
help with the goals of HDFS-7836, especially multi-threading block report processing and getting
the heap below 32GB in the long term.  Right now I don't see a path from this patch to there
but very possibly I'm missing something.  Let's chat about it sometime next week.

> 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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