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Update version on hadoop versions to include note on hadoop 1.0.0 

git-svn-id: https://svn.apache.org/repos/asf/hbase/trunk@1232308 13f79535-47bb-0310-9956-ffa450edef68
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Michael Stack 2012-01-17 05:15:44 +00:00
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@ -212,35 +212,44 @@ to ensure well-formedness of your document after an edit session.
xlink:href="http://hadoop.apache.org">Hadoop</link><indexterm>
<primary>Hadoop</primary>
</indexterm></title>
<note><title>Please read all of this section</title>
<para>Please read this section to the end. Up front we
wade through the weeds of Hadoop versions. Later we talk of what you must do in HBase
to make it work w/ a particular Hadoop version.</para>
</note>
<note>
<title>On Hadoop Versions?</title>
<para>
HBase will lose data unless it is running on an HDFS that has a durable
<code>sync</code> implementation. Hadoop 0.20.2, Hadoop 0.20.203.0, and Hadoop 0.20.204.0
DO NOT have this attribute.
Currently only Hadoop versions 0.20.205.x or any release in excess of this
version -- this includes hadoop 1.0.0 -- have a working, durable sync
<footnote>
<title>On Hadoop Versions</title>
<para>The Cloudera blog post <link xlink:href="http://www.cloudera.com/blog/2012/01/an-update-on-apache-hadoop-1-0/">An update on Apache Hadoop 1.0</link>
by Charles Zedlweski has a nice exposition on how all the Hadoop versions relate.
Its worth checking out if you are having trouble making sense of the
Hadoop version morass.
</para>
</note>
<para>
This version of HBase will only run on <link
xlink:href="http://hadoop.apache.org/common/releases.html">Hadoop
0.20.x</link>. It will not run on hadoop 0.21.x (but may run on 0.22.x/0.23.x).
HBase will lose data unless it is running on an HDFS that has a durable
<code>sync</code>. Hadoop 0.20.2, Hadoop 0.20.203.0, and Hadoop 0.20.204.0
DO NOT have this attribute.
Currently only Hadoop versions 0.20.205.x or any release in excess of this
version has a durable sync. You have to explicitly enable it though by
setting <varname>dfs.support.append</varname> equal to true on both
the client side -- in <filename>hbase-site.xml</filename> though it should
be on in your <filename>base-default.xml</filename> file -- and on the
serverside in <filename>hdfs-site.xml</filename> (You will have to restart
your cluster after setting this configuration). Ignore the chicken-little
comment you'll find in the <filename>hdfs-site.xml</filename> in the
description for this configuration; it says it is not enabled because there
</footnote>. Sync has to be explicitly enabled by setting
<varname>dfs.support.append</varname> equal
to true on both the client side -- in <filename>hbase-site.xml</filename>
-- and on the serverside in <filename>hdfs-site.xml</filename> (The sync
facility HBase needs is a subset of the append code path).
<programlisting>
&lt;property>
&lt;name>dfs.support.append&lt;/name>
&lt;value>true&lt;/value>
&lt;/property>
</programlisting>
You will have to restart your cluster after making this edit. Ignore the chicken-little
comment you'll find in the <filename>hdfs-default.xml</filename> in the
description for the <varname>dfs.support.append</varname> configuration; it says it is not enabled because there
are <quote>... bugs in the 'append code' and is not supported in any production
cluster.</quote> because it is not true (I'm sure there are bugs but the
append code has been running in production at large scale deploys and is on
by default in the offerings of hadoop by commercial vendors)
cluster.</quote>. This comment is stale, from another era, and while I'm sure there
are bugs, the sync/append code has been running
in production at large scale deploys and is on
by default in the offerings of hadoop by commercial vendors
<footnote><para>Until recently only the
<link xlink:href="http://svn.apache.org/viewvc/hadoop/common/branches/branch-0.20-append/">branch-0.20-append</link>
branch had a working sync but no official release was ever made from this branch.