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From "Liang Xie (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-4697) short-circuit reads do not honor readahead settings
Date Mon, 15 Apr 2013 23:40:16 GMT

    [ https://issues.apache.org/jira/browse/HDFS-4697?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13632370#comment-13632370
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Liang Xie commented on HDFS-4697:
---------------------------------

If that's true, the sequence read in HBase, e.g. large scan is suboptimal, right?   nice finding!
                
> short-circuit reads do not honor readahead settings
> ---------------------------------------------------
>
>                 Key: HDFS-4697
>                 URL: https://issues.apache.org/jira/browse/HDFS-4697
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: hdfs-client
>    Affects Versions: 2.0.3-alpha
>            Reporter: Colin Patrick McCabe
>            Assignee: Colin Patrick McCabe
>            Priority: Minor
>
> Neither the new nor the legacy short-circuit read implementations honor {{dfs.datanode.readahead.bytes}}.
 This can result in scenarios where non-short-circuit reads are faster for long reads, simply
because they are doing more readahead, and SCR is not.  We should do readahead in both cases
if it is configured.

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