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https://issues.apache.org/jira/browse/HDFS-3429?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13493874#comment-13493874
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Hadoop QA commented on HDFS-3429:
---------------------------------

{color:red}-1 overall{color}.  Here are the results of testing the latest 
attachment 
  
http://issues.apache.org/jira/secure/attachment/12552806/hdfs-3429-0.20.2.patch
  against trunk revision .

    {color:red}-1 patch{color}.  The patch command could not apply the patch.

Console output: https://builds.apache.org/job/PreCommit-HDFS-Build/3473//console

This message is automatically generated.
                
> DataNode reads checksums even if client does not need them
> ----------------------------------------------------------
>
>                 Key: HDFS-3429
>                 URL: https://issues.apache.org/jira/browse/HDFS-3429
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: data-node, performance
>    Affects Versions: 2.0.0-alpha
>            Reporter: Todd Lipcon
>            Assignee: Todd Lipcon
>         Attachments: hdfs-3429-0.20.2.patch, hdfs-3429.txt
>
>
> Currently, even if the client does not want to verify checksums, the datanode 
> reads them anyway and sends them over the wire. This means that performance 
> improvements like HBase's application-level checksums don't have much benefit 
> when reading through the datanode, since the DN is still causing seeks into 
> the checksum file.
> (Credit goes to Dhruba for discovering this - filing on his behalf)

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