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<a href="../../hadoop-mapreduce-client/hadoop-mapreduce-client-core/EncryptedShuffle.html">Encrypted Shuffle</a>
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<h5>MapReduce REST APIs</h5>
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<a href="../../hadoop-mapreduce-client/hadoop-mapreduce-client-hs/HistoryServerRest.html">MR History Server</a>
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<h5>YARN</h5>
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<ul>
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<a href="../../hadoop-yarn/hadoop-yarn-site/YARN.html">Architecture</a>
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<a href="../../hadoop-yarn/hadoop-yarn-site/YarnCommands.html">Commands Reference</a>
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<a href="../../hadoop-yarn/hadoop-yarn-site/ResourceManagerHA.html">ResourceManager HA</a>
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<a href="../../hadoop-yarn/hadoop-yarn-site/ResourceModel.html">Resource Model</a>
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<a href="../../hadoop-yarn/hadoop-yarn-site/NodeLabel.html">Node Labels</a>
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<a href="../../hadoop-yarn/hadoop-yarn-site/NodeAttributes.html">Node Attributes</a>
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<a href="../../hadoop-yarn/hadoop-yarn-site/WebApplicationProxy.html">Web Application Proxy</a>
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<a href="../../hadoop-yarn/hadoop-yarn-site/TimelineServer.html">Timeline Server</a>
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<a href="../../hadoop-yarn/hadoop-yarn-site/TimelineServiceV2.html">Timeline Service V.2</a>
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<a href="../../hadoop-yarn/hadoop-yarn-site/WritingYarnApplications.html">Writing YARN Applications</a>
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<a href="../../hadoop-yarn/hadoop-yarn-site/YarnApplicationSecurity.html">YARN Application Security</a>
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<a href="../../hadoop-yarn/hadoop-yarn-site/NodeManager.html">NodeManager</a>
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<a href="../../hadoop-yarn/hadoop-yarn-site/DockerContainers.html">Running Applications in Docker Containers</a>
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<a href="../../hadoop-yarn/hadoop-yarn-site/RuncContainers.html">Running Applications in runC Containers</a>
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<a href="../../hadoop-yarn/hadoop-yarn-site/NodeManagerCgroups.html">Using CGroups</a>
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<a href="../../hadoop-yarn/hadoop-yarn-site/SecureContainer.html">Secure Containers</a>
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<a href="../../hadoop-yarn/hadoop-yarn-site/ReservationSystem.html">Reservation System</a>
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<a href="../../hadoop-yarn/hadoop-yarn-site/GracefulDecommission.html">Graceful Decommission</a>
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<a href="../../hadoop-yarn/hadoop-yarn-site/OpportunisticContainers.html">Opportunistic Containers</a>
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<a href="../../hadoop-yarn/hadoop-yarn-site/Federation.html">YARN Federation</a>
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<a href="../../hadoop-yarn/hadoop-yarn-site/SharedCache.html">Shared Cache</a>
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<a href="../../hadoop-yarn/hadoop-yarn-site/UsingGpus.html">Using GPU</a>
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<a href="../../hadoop-yarn/hadoop-yarn-site/UsingFPGA.html">Using FPGA</a>
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<a href="../../hadoop-yarn/hadoop-yarn-site/PlacementConstraints.html">Placement Constraints</a>
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<a href="../../hadoop-yarn/hadoop-yarn-site/YarnUI2.html">YARN UI2</a>
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</li>
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</ul>
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<h5>YARN REST APIs</h5>
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<ul>
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<li class="none">
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<a href="../../hadoop-yarn/hadoop-yarn-site/WebServicesIntro.html">Introduction</a>
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</li>
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<li class="none">
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<a href="../../hadoop-yarn/hadoop-yarn-site/ResourceManagerRest.html">Resource Manager</a>
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<a href="../../hadoop-yarn/hadoop-yarn-site/NodeManagerRest.html">Node Manager</a>
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</li>
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<li class="none">
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<a href="../../hadoop-yarn/hadoop-yarn-site/TimelineServer.html#Timeline_Server_REST_API_v1">Timeline Server</a>
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</li>
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<li class="none">
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<a href="../../hadoop-yarn/hadoop-yarn-site/TimelineServiceV2.html#Timeline_Service_v.2_REST_API">Timeline Service V.2</a>
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</li>
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</ul>
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<h5>YARN Service</h5>
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<ul>
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<li class="none">
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<a href="../../hadoop-yarn/hadoop-yarn-site/yarn-service/Overview.html">Overview</a>
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</li>
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<li class="none">
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<a href="../../hadoop-yarn/hadoop-yarn-site/yarn-service/QuickStart.html">QuickStart</a>
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<a href="../../hadoop-yarn/hadoop-yarn-site/yarn-service/Concepts.html">Concepts</a>
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<li class="none">
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<a href="../../hadoop-yarn/hadoop-yarn-site/yarn-service/YarnServiceAPI.html">Yarn Service API</a>
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<li class="none">
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<a href="../../hadoop-yarn/hadoop-yarn-site/yarn-service/ServiceDiscovery.html">Service Discovery</a>
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<li class="none">
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<a href="../../hadoop-yarn/hadoop-yarn-site/yarn-service/SystemServices.html">System Services</a>
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</li>
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</ul>
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<h5>Hadoop Compatible File Systems</h5>
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<ul>
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<li class="none">
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<a href="../../hadoop-aliyun/tools/hadoop-aliyun/index.html">Aliyun OSS</a>
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</li>
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<li class="none">
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<a href="../../hadoop-aws/tools/hadoop-aws/index.html">Amazon S3</a>
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</li>
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<li class="none">
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<a href="../../hadoop-azure/index.html">Azure Blob Storage</a>
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</li>
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<li class="none">
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<a href="../../hadoop-azure-datalake/index.html">Azure Data Lake Storage</a>
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</li>
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<li class="none">
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<a href="../../hadoop-cos/cloud-storage/index.html">Tencent COS</a>
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</li>
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<li class="none">
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<a href="../../hadoop-huaweicloud/cloud-storage/index.html">Huaweicloud OBS</a>
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</li>
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</ul>
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<h1>C API libhdfs</h1>
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<ul>
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<li><a href="#Overview">Overview</a></li>
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<li><a href="#The_APIs">The APIs</a></li>
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<li><a href="#A_Sample_Program">A Sample Program</a></li>
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<li><a href="#How_To_Link_With_The_Library">How To Link With The Library</a></li>
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<li><a href="#Common_Problems">Common Problems</a></li>
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<li><a href="#Thread_Safe">Thread Safe</a></li></ul>
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<section>
|
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<h2><a name="Overview"></a>Overview</h2>
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<p>libhdfs is a JNI based C API for Hadoop’s Distributed File System (HDFS). It provides C APIs to a subset of the HDFS APIs to manipulate HDFS files and the filesystem. libhdfs is part of the Hadoop distribution and comes pre-compiled in <code>$HADOOP_HDFS_HOME/lib/native/libhdfs.so</code> . libhdfs is compatible with Windows and can be built on Windows by running <code>mvn compile</code> within the <code>hadoop-hdfs-project/hadoop-hdfs</code> directory of the source tree.</p></section><section>
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<h2><a name="The_APIs"></a>The APIs</h2>
|
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<p>The libhdfs APIs are a subset of the <a href="../../api/org/apache/hadoop/fs/FileSystem.html">Hadoop FileSystem APIs</a>.</p>
|
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<p>The header file for libhdfs describes each API in detail and is available in <code>$HADOOP_HDFS_HOME/include/hdfs.h</code>.</p></section><section>
|
|
<h2><a name="A_Sample_Program"></a>A Sample Program</h2>
|
|
|
|
<div class="source">
|
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<div class="source">
|
|
<pre>#include "hdfs.h"
|
|
|
|
int main(int argc, char **argv) {
|
|
|
|
hdfsFS fs = hdfsConnect("default", 0);
|
|
const char* writePath = "/tmp/testfile.txt";
|
|
hdfsFile writeFile = hdfsOpenFile(fs, writePath, O_WRONLY |O_CREAT, 0, 0, 0);
|
|
if(!writeFile) {
|
|
fprintf(stderr, "Failed to open %s for writing!\n", writePath);
|
|
exit(-1);
|
|
}
|
|
char* buffer = "Hello, World!";
|
|
tSize num_written_bytes = hdfsWrite(fs, writeFile, (void*)buffer, strlen(buffer)+1);
|
|
if (hdfsFlush(fs, writeFile)) {
|
|
fprintf(stderr, "Failed to 'flush' %s\n", writePath);
|
|
exit(-1);
|
|
}
|
|
hdfsCloseFile(fs, writeFile);
|
|
}
|
|
</pre></div></div>
|
|
</section><section>
|
|
<h2><a name="How_To_Link_With_The_Library"></a>How To Link With The Library</h2>
|
|
<p>See the CMake file for <code>test_libhdfs_ops.c</code> in the libhdfs source directory (<code>hadoop-hdfs-project/hadoop-hdfs/src/CMakeLists.txt</code>) or something like: <code>gcc above_sample.c -I$HADOOP_HDFS_HOME/include -L$HADOOP_HDFS_HOME/lib/native -lhdfs -o above_sample</code></p></section><section>
|
|
<h2><a name="Common_Problems"></a>Common Problems</h2>
|
|
<p>The most common problem is the <code>CLASSPATH</code> is not set properly when calling a program that uses libhdfs. Make sure you set it to all the Hadoop jars needed to run Hadoop itself as well as the right configuration directory containing <code>hdfs-site.xml</code>. Wildcard entries in the <code>CLASSPATH</code> are now supported by libhdfs.</p></section><section>
|
|
<h2><a name="Thread_Safe"></a>Thread Safe</h2>
|
|
<p>libhdfs is thread safe.</p>
|
|
<ul>
|
|
|
|
<li>
|
|
|
|
<p>Concurrency and Hadoop FS “handles”</p>
|
|
<p>The Hadoop FS implementation includes an FS handle cache which caches based on the URI of the namenode along with the user connecting. So, all calls to <code>hdfsConnect</code> will return the same handle but calls to <code>hdfsConnectAsUser</code> with different users will return different handles. But, since HDFS client handles are completely thread safe, this has no bearing on concurrency.</p>
|
|
</li>
|
|
<li>
|
|
|
|
<p>Concurrency and libhdfs/JNI</p>
|
|
<p>The libhdfs calls to JNI should always be creating thread local storage, so (in theory), libhdfs should be as thread safe as the underlying calls to the Hadoop FS.</p>
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</li>
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</ul></section>
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