[jira] [Commented] (ACCUMULO-884) Take advantage of short circuit read for local files

["Colin Patrick McCabe (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/ACCUMULO-884?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13975730#comment-13975730 ] 

Colin Patrick McCabe commented on ACCUMULO-884:
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bq. A nice to have would be some stats on if reads are actually short circuiting, in the TServer logs or Monitor. I haven't chased down where to get this information, sadly.

Go to the Datanode's /jmx page and look for {{BlocksGetLocalPathInfo}}.  It will be greater than 0 if short-circuit reads are happening.

> 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: Sub-task
>          Components: docs
>            Reporter: Billie Rinaldi
>
> 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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