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<h1>Apache Hadoop 2.4.0 Release Notes</h1>
<p>These release notes cover new developer and user-facing incompatibilities, important issues, features, and major improvements.</p><hr />
<ul>
<li><a class="externalLink" href="https://issues.apache.org/jira/browse/HDFS-5790">HDFS-5790</a> | <i>Major</i> | <b>LeaseManager.findPath is very slow when many leases need recovery</b></li>
</ul>
<p>Committed to branch-2 and trunk.</p><hr />
<ul>
<li><a class="externalLink" href="https://issues.apache.org/jira/browse/HADOOP-10295">HADOOP-10295</a> | <i>Major</i> | <b>Allow distcp to automatically identify the checksum type of source files and use it for the target</b></li>
</ul>
<p>Add option for distcp to preserve the checksum type of the source files. Users can use &#x201c;-pc&#x201d; as distcp command option to preserve the checksum type.</p><hr />
<ul>
<li><a class="externalLink" href="https://issues.apache.org/jira/browse/HDFS-5804">HDFS-5804</a> | <i>Major</i> | <b>HDFS NFS Gateway fails to mount and proxy when using Kerberos</b></li>
</ul>
<p>Fixes NFS on Kerberized cluster.</p><hr />
<ul>
<li><a class="externalLink" href="https://issues.apache.org/jira/browse/HDFS-5698">HDFS-5698</a> | <i>Major</i> | <b>Use protobuf to serialize / deserialize FSImage</b></li>
</ul>
<p>Use protobuf to serialize/deserialize the FSImage.</p><hr />
<ul>
<li><a class="externalLink" href="https://issues.apache.org/jira/browse/HDFS-4370">HDFS-4370</a> | <i>Major</i> | <b>Fix typo Blanacer in DataNode</b></li>
</ul>
<p>I just committed this. Thank you Chu.</p><hr />
<ul>
<li><a class="externalLink" href="https://issues.apache.org/jira/browse/HDFS-5776">HDFS-5776</a> | <i>Major</i> | <b>Support &#x2018;hedged&#x2019; reads in DFSClient</b></li>
</ul>
<p>If a read from a block is slow, start up another parallel, &#x2018;hedged&#x2019; read against a different block replica. We then take the result of which ever read returns first (the outstanding read is cancelled). This &#x2018;hedged&#x2019; read feature will help rein in the outliers, the odd read that takes a long time because it hit a bad patch on the disc, etc.</p>
<p>This feature is off by default. To enable this feature, set &lt;code&gt;dfs.client.hedged.read.threadpool.size&lt;/code&gt; to a positive number. The threadpool size is how many threads to dedicate to the running of these &#x2018;hedged&#x2019;, concurrent reads in your client.</p>
<p>Then set &lt;code&gt;dfs.client.hedged.read.threshold.millis&lt;/code&gt; to the number of milliseconds to wait before starting up a &#x2018;hedged&#x2019; read. For example, if you set this property to 10, then if a read has not returned within 10 milliseconds, we will start up a new read against a different block replica.</p>
<p>This feature emits new metrics:</p>
<ul>
<li>hedgedReadOps</li>
<li>hedgeReadOpsWin &#x2013; how many times the hedged read &#x2018;beat&#x2019; the original read</li>
<li>hedgedReadOpsInCurThread &#x2013; how many times we went to do a hedged read but we had to run it in the current thread because dfs.client.hedged.read.threadpool.size was at a maximum.</li>
</ul><hr />
<ul>
<li><a class="externalLink" href="https://issues.apache.org/jira/browse/HADOOP-8691">HADOOP-8691</a> | <i>Minor</i> | <b>FsShell can print &#x201c;Found xxx items&#x201d; unnecessarily often</b></li>
</ul>
<p>The `ls` command only prints &#x201c;Found foo items&#x201d; once when listing the directories recursively.</p><hr />
<ul>
<li><a class="externalLink" href="https://issues.apache.org/jira/browse/HDFS-5321">HDFS-5321</a> | <i>Major</i> | <b>Clean up the HTTP-related configuration in HDFS</b></li>
</ul>
<p>dfs.http.port and dfs.https.port are removed. Filesystem clients, such as WebHdfsFileSystem, now have fixed instead of configurable default ports (i.e., 50070 for http and 50470 for https).</p>
<p>Users can explicitly specify the port in the URI to access the file system which runs on non-default ports.</p><hr />
<ul>
<li><a class="externalLink" href="https://issues.apache.org/jira/browse/HADOOP-10211">HADOOP-10211</a> | <i>Major</i> | <b>Enable RPC protocol to negotiate SASL-QOP values between clients and servers</b></li>
</ul>
<p>The hadoop.rpc.protection configuration property previously supported specifying a single value: one of authentication, integrity or privacy. An unrecognized value was silently assumed to mean authentication. This configuration property now accepts a comma-separated list of any of the 3 values, and unrecognized values are rejected with an error. Existing configurations containing an invalid value must be corrected. If the property is empty or not specified, authentication is assumed.</p><hr />
<ul>
<li><a class="externalLink" href="https://issues.apache.org/jira/browse/HDFS-6055">HDFS-6055</a> | <i>Major</i> | <b>Change default configuration to limit file name length in HDFS</b></li>
</ul>
<p>The default configuration of HDFS now sets dfs.namenode.fs-limits.max-component-length to 255 for improved interoperability with other file system implementations. This limits each component of a file system path to a maximum of 255 bytes in UTF-8 encoding. Attempts to create new files that violate this rule will fail with an error. Existing files that violate the rule are not effected. Previously, dfs.namenode.fs-limits.max-component-length was set to 0 (ignored). If necessary, it is possible to set the value back to 0 in the cluster&#x2019;s configuration to restore the old behavior.</p><hr />
<ul>
<li><a class="externalLink" href="https://issues.apache.org/jira/browse/HDFS-6102">HDFS-6102</a> | <i>Blocker</i> | <b>Lower the default maximum items per directory to fix PB fsimage loading</b></li>
</ul>
<p><b>WARNING: No release note provided for this change.</b></p><hr />
<ul>
<li><a class="externalLink" href="https://issues.apache.org/jira/browse/HADOOP-10221">HADOOP-10221</a> | <i>Major</i> | <b>Add a plugin to specify SaslProperties for RPC protocol based on connection properties</b></li>
</ul>
<p>SaslPropertiesResolver or its subclass is used to resolve the QOP used for a connection. The subclass can be specified via &#x201c;hadoop.security.saslproperties.resolver.class&#x201d; configuration property. If not specified, the full set of values specified in hadoop.rpc.protection is used while determining the QOP used for the connection. If a class is specified, then the QOP values returned by the class will be used while determining the QOP used for the connection.</p>
<p>Note that this change, effectively removes SaslRpcServer.SASL_PROPS which was a public field. Any use of this variable should be replaced with the following code: SaslPropertiesResolver saslPropsResolver = SaslPropertiesResolver.getInstance(conf); Map&lt;String, String&gt; sasl_props = saslPropsResolver.getDefaultProperties();</p><hr />
<ul>
<li><a class="externalLink" href="https://issues.apache.org/jira/browse/HDFS-4685">HDFS-4685</a> | <i>Major</i> | <b>Implementation of ACLs in HDFS</b></li>
</ul>
<p>HDFS now supports ACLs (Access Control Lists). ACLs can specify fine-grained file permissions for specific named users or named groups.</p><hr />
<ul>
<li><a class="externalLink" href="https://issues.apache.org/jira/browse/HDFS-5138">HDFS-5138</a> | <i>Blocker</i> | <b>Support HDFS upgrade in HA</b></li>
</ul>
<p><b>WARNING: No release note provided for this change.</b></p><hr />
<ul>
<li><a class="externalLink" href="https://issues.apache.org/jira/browse/MAPREDUCE-5036">MAPREDUCE-5036</a> | <i>Major</i> | <b>Default shuffle handler port should not be 8080</b></li>
</ul>
<p><b>WARNING: No release note provided for this change.</b></p>
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