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Added link to read short circuit dev conversation into read short circuit footnote 

git-svn-id: https://svn.apache.org/repos/asf/hbase/trunk@1384977 13f79535-47bb-0310-9956-ffa450edef68
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Michael Stack 2012-09-15 00:04:25 +00:00
parent 0dab826f19
commit dde1f3d451
1 changed files with 4 additions and 2 deletions
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6
src/docbkx/performance.xml
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@ -200,14 +200,16 @@
<title>Leveraging local data</title> <title>Leveraging local data</title>
<para>Since Hadoop 1.0.0 (also 0.22.1, 0.23.1, CDH3u3 and HDP 1.0) via <para>Since Hadoop 1.0.0 (also 0.22.1, 0.23.1, CDH3u3 and HDP 1.0) via
<link xlink:href="https://issues.apache.org/jira/browse/HDFS-2246">HDFS-2246</link>, <link xlink:href="https://issues.apache.org/jira/browse/HDFS-2246">HDFS-2246</link>,
it is possible for the DFSClient to take a shortcut and it is possible for the DFSClient to take a "short circuit" and
read directly from disk instead of going through the DataNode when the read directly from disk instead of going through the DataNode when the
data is local. What this means for HBase is that the RegionServers can data is local. What this means for HBase is that the RegionServers can
read directly off their machine's disks instead of having to open a read directly off their machine's disks instead of having to open a
socket to talk to the DataNode, the former being generally much socket to talk to the DataNode, the former being generally much
faster<footnote><para>See JD's <link xlink:href="http://files.meetup.com/1350427/hug_ebay_jdcryans.pdf">Performance Talk</link></para></footnote>. faster<footnote><para>See JD's <link xlink:href="http://files.meetup.com/1350427/hug_ebay_jdcryans.pdf">Performance Talk</link></para></footnote>.
Also see <link xlink:href="http://search-hadoop.com/m/zV6dKrLCVh1">HBase, mail # dev - read short circuit</link> thread for
more discussion around short circuit reads.
</para> </para>
<para>To enable "shortcircuit" reads, you must set two configurations. <para>To enable "short circuit" reads, you must set two configurations.
First, the hdfs-site.xml needs to be amended. Set First, the hdfs-site.xml needs to be amended. Set
the property <varname>dfs.block.local-path-access.user</varname> the property <varname>dfs.block.local-path-access.user</varname>
to be the <emphasis>only</emphasis> user that can use the shortcut. to be the <emphasis>only</emphasis> user that can use the shortcut.