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From "Billie Rinaldi (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (ACCUMULO-884) Take advantage of short circuit read for local files
Date Wed, 28 Nov 2012 19:10:58 GMT

    [ https://issues.apache.org/jira/browse/ACCUMULO-884?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13505797#comment-13505797
] 

Billie Rinaldi commented on ACCUMULO-884:
-----------------------------------------

On that HBase page it says: "Be aware that if a process started under another username than
the one configured here also has the shortcircuit enabled, it will get an Exception regarding
an unauthorized access but the data will still be read."  We should try it out.
                
> Take advantage of short circuit read for local files
> ----------------------------------------------------
>
>                 Key: ACCUMULO-884
>                 URL: https://issues.apache.org/jira/browse/ACCUMULO-884
>             Project: Accumulo
>          Issue Type: Improvement
>          Components: docs
>            Reporter: Billie Rinaldi
>             Fix For: 1.5.0
>
>
> This is a new feature in hadoop 1.0.x and some versions of 0.22 and 0.23.  It allows
a client to read directly from disk instead of through a DataNode when the data is stored
locally.  Enabling it involves setting two configuration parameters, the first in hdfs-site.xml
and the second in accumulo-site.xml.  We should make sure this works with Accumulo and recommend
it in the documentation.
> - dfs.block.local-path-access.user is the key in datanode configuration to specify the
user allowed to do short circuit read.
> - dfs.client.read.shortcircuit is the key to enable short circuit read at the client
side configuration.
> See HDFS-2246 and http://hbase.apache.org/book/perf.hdfs.configs.html for more information.

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