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From "Colin Patrick McCabe (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-4453) Make a simple doc to describe the usage and design of the shortcircuit read feature
Date Sat, 02 Feb 2013 01:35:11 GMT

    [ https://issues.apache.org/jira/browse/HDFS-4453?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13569354#comment-13569354

Colin Patrick McCabe commented on HDFS-4453:

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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