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https://issues.apache.org/jira/browse/HADOOP-2758?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12569122#action_12569122
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Raghu Angadi commented on HADOOP-2758:
--------------------------------------

With 6 instances of 'dfs -cat 5GbFile > /dev/null' both tests were cpu bound.

with out the patch : ~ 6.5 min
with the patch : ~ 3.5 min.

> Reduce memory copies when data is read from DFS
> -----------------------------------------------
>
>                 Key: HADOOP-2758
>                 URL: https://issues.apache.org/jira/browse/HADOOP-2758
>             Project: Hadoop Core
>          Issue Type: Improvement
>          Components: dfs
>            Reporter: Raghu Angadi
>            Assignee: Raghu Angadi
>             Fix For: 0.17.0
>
>         Attachments: HADOOP-2758.patch
>
>
> Currently datanode and client part of DFS perform multiple copies of data on 
> the 'read path' (i.e. path from storage on datanode to user buffer on the 
> client). This jira reduces these copies by enhancing data read protocol and 
> implementation of read on both datanode and the client. I will describe the 
> changes in next comment.
> Requirement is that this fix should reduce CPU used and should not cause 
> regression in any benchmarks. It might not improve the benchmarks since most 
> benchmarks are not cpu bound.

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