Apache
/
hbase
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

More fixup around SCR. Add sample config. Remove the whole section on checksum verify. It is what we have on by default now so don't call it out; only confuses 

git-svn-id: https://svn.apache.org/repos/asf/hbase/trunk@1591110 13f79535-47bb-0310-9956-ffa450edef68
This commit is contained in:
Michael Stack 2014-04-29 21:29:38 +00:00
parent 58e36777b4
commit 56c0f89c82
1 changed files with 21 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

29
src/main/docbkx/performance.xml
View File

@ -687,6 +687,27 @@ more discussion around short circuit reads.
on the difference between the old and new implementations. See
<link xlink:href="http://archive.cloudera.com/cdh4/cdh/4/hadoop/hadoop-project-dist/hadoop-hdfs/ShortCircuitLocalReads.html">Hadoop shortcircuit reads configuration page</link>
for how to enable the latter, better version of shortcircuit.
For example, here is a minimal config. enabling short-circuit reads added to
<filename>hbase-site.xml</filename>:
<programlisting><![CDATA[<property>
<name>dfs.client.read.shortcircuit</name>
<value>true</value>
<description>
This configuration parameter turns on short-circuit local reads.
</description>
</property>
<property>
<name>dfs.domain.socket.path</name>
<value>/home/stack/sockets/short_circuit_read_socket_PORT</value>
<description>
Optional. This is a path to a UNIX domain socket that will be used for
communication between the DataNode and local HDFS clients.
If the string "_PORT" is present in this path, it will be replaced by the
TCP port of the DataNode.
</description>
</property>]]></programlisting>
Be careful about permissions for the directory that hosts the shared domain
socket; dfsclient will complain if open to other than the hbase user.
<footnote><para>If you are running on an old Hadoop, one that is without
<link xlink:href="https://issues.apache.org/jira/browse/HDFS-347">HDFS-347</link> but that
has
@ -699,14 +720,6 @@ This has to be the user that started HBase. Then in hbase-site.xml,
set <varname>dfs.client.read.shortcircuit</varname> to be <varname>true</varname>
</para></footnote>
</para>
<para>
With short-circuit enabled, for more speed-up, it is recommended that you have HBase do the checksum validation. HBase writes
checksums inline with the data whereas HDFS keeps checksums in a separate file that it must seek independent of
the data file. Set <xref linkend="hbase.regionserver.checksum.verify" /> to have HBase do checksum validation.
While you might think it safe to set the HDFS configuration parameter "dfs.client.read.shortcircuit.skip.checksum",
you should NOT; HBase checksum validation covers hfiles only, not WAL files and if the HBase checksum validation fails,
we will fall back on HDFS's.
</para>
<para>
Services -- at least the HBase RegionServers -- will need to be restarted in order to pick up the new
configurations.