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