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From "Andrew Ash (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-4697) short-circuit reads do not honor readahead settings
Date Wed, 01 Oct 2014 01:17:34 GMT

    [ https://issues.apache.org/jira/browse/HDFS-4697?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14154167#comment-14154167

Andrew Ash commented on HDFS-4697:

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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