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<h1>Hadoop Archives</h1>
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<li>
<a href="#%E4%BB%80%E4%B9%88%E6%98%AFHadoop+archives%3F"> 什么是Hadoop archives? </a>
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<a href="#%E5%A6%82%E4%BD%95%E5%88%9B%E5%BB%BAarchive%3F"> 如何创建archive? </a>
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<a href="#%E5%A6%82%E4%BD%95%E6%9F%A5%E7%9C%8Barchives%E4%B8%AD%E7%9A%84%E6%96%87%E4%BB%B6%3F"> 如何查看archives中的文件? </a>
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<a name="N1000D"></a><a name="%E4%BB%80%E4%B9%88%E6%98%AFHadoop+archives%3F"></a>
<h2 class="h3"> 什么是Hadoop archives? </h2>
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<p>
Hadoop archives是特殊的档案格式。一个Hadoop archive对应一个文件系统目录。
Hadoop archive的扩展名是*.har。Hadoop archive包含元数据(形式是_index和_masterindx)和数据(part-*)文件。_index文件包含了档案中的文件的文件名和位置信息。
</p>
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<a name="N10017"></a><a name="%E5%A6%82%E4%BD%95%E5%88%9B%E5%BB%BAarchive%3F"></a>
<h2 class="h3"> 如何创建archive? </h2>
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<p>
<span class="codefrag">用法: hadoop archive -archiveName name &lt;src&gt;* &lt;dest&gt;</span>
</p>
<p>
由-archiveName选项指定你要创建的archive的名字。比如foo.har。archive的名字的扩展名应该是*.har。输入是文件系统的路径名,路径名的格式和平时的表达方式一样。创建的archive会保存到目标目录下。注意创建archives是一个Map/Reduce job。你应该在map reduce集群上运行这个命令。下面是一个例子:
</p>
<p>
<span class="codefrag">hadoop archive -archiveName foo.har /user/hadoop/dir1 /user/hadoop/dir2 /user/zoo/</span>
</p>
<p>
在上面的例子中,
/user/hadoop/dir1 和 /user/hadoop/dir2 会被归档到这个文件系统目录下
-- /user/zoo/foo.har。当创建archive时,源文件不会被更改或删除。
</p>
</div>
<a name="N1002F"></a><a name="%E5%A6%82%E4%BD%95%E6%9F%A5%E7%9C%8Barchives%E4%B8%AD%E7%9A%84%E6%96%87%E4%BB%B6%3F"></a>
<h2 class="h3"> 如何查看archives中的文件? </h2>
<div class="section">
<p>
archive作为文件系统层暴露给外界。所以所有的fs shell命令都能在archive上运行,但是要使用不同的URI。
另外,archive是不可改变的。所以重命名,删除和创建都会返回错误。Hadoop Archives 的URI是
</p>
<p>
<span class="codefrag">har://scheme-hostname:port/archivepath/fileinarchive</span>
</p>
<p>
如果没提供scheme-hostname,它会使用默认的文件系统。这种情况下URI是这种形式
</p>
<p>
<span class="codefrag">
har:///archivepath/fileinarchive</span>
</p>
<p>
这是一个archive的例子。archive的输入是/dir。这个dir目录包含文件filea,fileb。
把/dir归档到/user/hadoop/foo.bar的命令是
</p>
<p>
<span class="codefrag">hadoop archive -archiveName foo.har /dir /user/hadoop</span>
</p>
<p>
获得创建的archive中的文件列表,使用命令
</p>
<p>
<span class="codefrag">hadoop dfs -lsr har:///user/hadoop/foo.har</span>
</p>
<p>查看archive中的filea文件的命令-
</p>
<p>
<span class="codefrag">hadoop dfs -cat har:///user/hadoop/foo.har/dir/filea</span>
</p>
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