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From "Raghu Angadi (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-2758) Reduce memory copies when data is read from DFS
Date Fri, 15 Feb 2008 03:37:07 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-2758?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12569166#action_12569166
] 

Raghu Angadi commented on HADOOP-2758:
--------------------------------------

Thanks for the detailed review Konstatin.

Just a clarification to the readers: except 4 and 7, rest are not introduced by this patch.
I will try to fix some of them.

When this protocol was first introduced, it was described in the jira (HADOOP-1134). Since
then, it has evolved. I agree that it will be better to have the ascii diagrams in the code
comments itself. I will surely add that.


> 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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