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From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-3429) DataNode reads checksums even if client does not need them
Date Thu, 22 Nov 2012 00:11:00 GMT

    [ https://issues.apache.org/jira/browse/HDFS-3429?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13502463#comment-13502463
] 

Todd Lipcon commented on HDFS-3429:
-----------------------------------

Hi Liu Lei. FYI, since 0.20.x and 1.0.x are stable branches, we can't make protocol-incompatible
changes like this. We either need to figure out a creative hack which would allow for wire
compatibility, or else keep this feature only targeted at 2.x, where protobufs allow us to
safely make these types of changes.
                
> 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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