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https://issues.apache.org/jira/browse/HDFS-4697?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14154167#comment-14154167
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Andrew Ash commented on HDFS-4697:
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Hi [~cmccabe] are the short-circuit reads using readahead settings properly 
now?  If so this ticket is good to close

> 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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