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Date: Wed, 21 Nov 2012 08:46:03 +0000 (UTC)
From: "Hadoop QA (JIRA)" <jira@apache.org>
To: hdfs-issues@hadoop.apache.org
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Subject: [jira] [Commented] (HDFS-3429) DataNode reads checksums even if
 client does not need them
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    [ https://issues.apache.org/jira/browse/HDFS-3429?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13501774#comment-13501774 ] 

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/12554468/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/3552//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-3429-0.20.2.patch, hdfs-3429.txt, hdfs-3429.txt, 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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