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https://issues.apache.org/jira/browse/HDFS-4453?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13569354#comment-13569354
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Colin Patrick McCabe commented on HDFS-4453:
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bq. Regarding /var/lib/hadoop-hdfs vs /var/run/hadoop-hdfs – why's it
problematic if /var/run is a tmpfs? We shouldn't need it to persist
cross-reboot, and /var/run is generally not cleaned by a tmpwatch process.
tmpfs is also better in that it will continue to work even if a local disk dies.
If the /var/run/hadoop-hdfs directory gets removed, hdfs itself can't recreate
it (you need root permissions to create a directory in /var/run.) So after a
reboot, things would probably stop working.
> Make a simple doc to describe the usage and design of the shortcircuit read
> feature
> -----------------------------------------------------------------------------------
>
> Key: HDFS-4453
> URL: https://issues.apache.org/jira/browse/HDFS-4453
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Components: datanode, hdfs-client
> Reporter: Brandon Li
> Assignee: Colin Patrick McCabe
> Attachments: HDFS-4453.001.patch, HDFS-4453.002.patch
>
>
> It would be nice to have a document to describe the configuration and design
> of this feature. Also its relationship with previous short circuit read
> implementation(HDFS-2246), for example, can they co-exist, or this one is
> planed to replaces HDFS-2246, or it can fall back on HDFS-2246 when unix
> domain socket is not supported.
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