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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:
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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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