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From "dhruba borthakur (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-3429) DataNode reads checksums even if client does not need them
Date Wed, 16 May 2012 07:14:09 GMT

    [ https://issues.apache.org/jira/browse/HDFS-3429?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13276537#comment-13276537
] 

dhruba borthakur commented on HDFS-3429:
----------------------------------------

For the records, if you switch-on local read shortcircuit, then the read of the checksum file
is avoided.
                
> 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
>            Reporter: Todd Lipcon
>
> 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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