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https://issues.apache.org/jira/browse/HDFS-3429?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13538830#comment-13538830
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liang xie commented on HDFS-3429:
---------------------------------
i'm sorry, i didn't have a test env to retry this week...
> 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: datanode, 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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