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https://issues.apache.org/jira/browse/HDFS-3697?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Todd Lipcon updated HDFS-3697:
------------------------------
Release Note: The datanode now performs 4MB readahead by default when
reading data from its disks, if the native libraries are present. This has been
shown to improve performance in many workloads. The feature may be disabled by
setting dfs.datanode.readahead.bytes to "0".
> Enable fadvise readahead by default
> -----------------------------------
>
> Key: HDFS-3697
> URL: https://issues.apache.org/jira/browse/HDFS-3697
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: data-node, performance
> Affects Versions: 3.0.0, 2.2.0-alpha
> Reporter: Todd Lipcon
> Assignee: Todd Lipcon
> Priority: Minor
> Fix For: 3.0.0, 2.2.0-alpha
>
> Attachments: hdfs-3697-branch-1.txt, hdfs-3697.txt, hdfs-3697.txt
>
>
> The fadvise features have been implemented for some time, and we've enabled
> them in production at a lot of customer sites without difficulty. I'd like to
> enable the readahead feature by default in future versions so that users get
> this benefit without any manual configuration required.
> The other fadvise features seem to be more workload-dependent and need
> further testing before enabling by default.
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