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| <h1>Hadoop Cluster Setup</h1> |
| <div id="minitoc-area"> |
| <ul class="minitoc"> |
| <li> |
| <a href="#Purpose">Purpose</a> |
| </li> |
| <li> |
| <a href="#Pre-requisites">Pre-requisites</a> |
| </li> |
| <li> |
| <a href="#Installation">Installation</a> |
| </li> |
| <li> |
| <a href="#Configuration">Configuration</a> |
| <ul class="minitoc"> |
| <li> |
| <a href="#Configuration+Files">Configuration Files</a> |
| </li> |
| <li> |
| <a href="#Site+Configuration">Site Configuration</a> |
| <ul class="minitoc"> |
| <li> |
| <a href="#Configuring+the+Environment+of+the+Hadoop+Daemons">Configuring the Environment of the Hadoop Daemons</a> |
| </li> |
| <li> |
| <a href="#Configuring+the+Hadoop+Daemons">Configuring the Hadoop Daemons</a> |
| </li> |
| <li> |
| <a href="#Slaves">Slaves</a> |
| </li> |
| <li> |
| <a href="#Logging">Logging</a> |
| </li> |
| </ul> |
| </li> |
| </ul> |
| </li> |
| <li> |
| <a href="#Hadoop+Rack+Awareness">Hadoop Rack Awareness</a> |
| </li> |
| <li> |
| <a href="#Hadoop+Startup">Hadoop Startup</a> |
| </li> |
| <li> |
| <a href="#Hadoop+Shutdown">Hadoop Shutdown</a> |
| </li> |
| </ul> |
| </div> |
| |
| |
| <a name="N1000D"></a><a name="Purpose"></a> |
| <h2 class="h3">Purpose</h2> |
| <div class="section"> |
| <p>This document describes how to install, configure and manage non-trivial |
| Hadoop clusters ranging from a few nodes to extremely large clusters with |
| thousands of nodes.</p> |
| <p>If you are looking to install Hadoop on a single machine to play |
| with it, you can find relevant details <a href="quickstart.html">here</a>. |
| </p> |
| </div> |
| |
| |
| <a name="N1001E"></a><a name="Pre-requisites"></a> |
| <h2 class="h3">Pre-requisites</h2> |
| <div class="section"> |
| <ol> |
| |
| <li> |
| Make sure all <a href="quickstart.html#PreReqs">requisite</a> software |
| is installed on all nodes in your cluster. |
| </li> |
| |
| <li> |
| |
| <a href="quickstart.html#Download">Get</a> the Hadoop software. |
| </li> |
| |
| </ol> |
| </div> |
| |
| |
| <a name="N10036"></a><a name="Installation"></a> |
| <h2 class="h3">Installation</h2> |
| <div class="section"> |
| <p>Installing a Hadoop cluster typically involves unpacking the software |
| on all the machines in the cluster.</p> |
| <p>Typically one machine in the cluster is designated as the |
| <span class="codefrag">NameNode</span> and another machine the as <span class="codefrag">JobTracker</span>, |
| exclusively. These are the <em>masters</em>. The rest of the machines in |
| the cluster act as both <span class="codefrag">DataNode</span> <em>and</em> |
| <span class="codefrag">TaskTracker</span>. These are the <em>slaves</em>.</p> |
| <p>The root of the distribution is referred to as |
| <span class="codefrag">HADOOP_HOME</span>. All machines in the cluster usually have the same |
| <span class="codefrag">HADOOP_HOME</span> path.</p> |
| </div> |
| |
| |
| <a name="N10061"></a><a name="Configuration"></a> |
| <h2 class="h3">Configuration</h2> |
| <div class="section"> |
| <p>The following sections describe how to configure a Hadoop cluster.</p> |
| <a name="N1006A"></a><a name="Configuration+Files"></a> |
| <h3 class="h4">Configuration Files</h3> |
| <p>Hadoop configuration is driven by two important configuration files |
| found in the <span class="codefrag">conf/</span> directory of the distribution:</p> |
| <ol> |
| |
| <li> |
| |
| <a href="http://hadoop.apache.org/core/docs/current/hadoop-default.html">hadoop-default.xml</a> - Read-only |
| default configuration. |
| </li> |
| |
| <li> |
| |
| <em>hadoop-site.xml</em> - Site-specific configuration. |
| </li> |
| |
| </ol> |
| <p>To learn more about how the Hadoop framework is controlled by these |
| configuration files, look |
| <a href="api/org/apache/hadoop/conf/Configuration.html">here</a>.</p> |
| <p>Additionally, you can control the Hadoop scripts found in the |
| <span class="codefrag">bin/</span> directory of the distribution, by setting site-specific |
| values via the <span class="codefrag">conf/hadoop-env.sh</span>.</p> |
| <a name="N10097"></a><a name="Site+Configuration"></a> |
| <h3 class="h4">Site Configuration</h3> |
| <p>To configure the the Hadoop cluster you will need to configure the |
| <em>environment</em> in which the Hadoop daemons execute as well as |
| the <em>configuration parameters</em> for the Hadoop daemons.</p> |
| <p>The Hadoop daemons are <span class="codefrag">NameNode</span>/<span class="codefrag">DataNode</span> |
| and <span class="codefrag">JobTracker</span>/<span class="codefrag">TaskTracker</span>.</p> |
| <a name="N100B5"></a><a name="Configuring+the+Environment+of+the+Hadoop+Daemons"></a> |
| <h4>Configuring the Environment of the Hadoop Daemons</h4> |
| <p>Administrators should use the <span class="codefrag">conf/hadoop-env.sh</span> script |
| to do site-specific customization of the Hadoop daemons' process |
| environment.</p> |
| <p>At the very least you should specify the |
| <span class="codefrag">JAVA_HOME</span> so that it is correctly defined on each |
| remote node.</p> |
| <p>Other useful configuration parameters that you can customize |
| include:</p> |
| <ul> |
| |
| <li> |
| |
| <span class="codefrag">HADOOP_LOG_DIR</span> - The directory where the daemons' |
| log files are stored. They are automatically created if they don't |
| exist. |
| </li> |
| |
| <li> |
| |
| <span class="codefrag">HADOOP_HEAPSIZE</span> - The maximum amount of heapsize |
| to use, in MB e.g. <span class="codefrag">2000MB</span>. |
| </li> |
| |
| </ul> |
| <a name="N100DD"></a><a name="Configuring+the+Hadoop+Daemons"></a> |
| <h4>Configuring the Hadoop Daemons</h4> |
| <p>This section deals with important parameters to be specified in the |
| <span class="codefrag">conf/hadoop-site.xml</span> for the Hadoop cluster.</p> |
| <table class="ForrestTable" cellspacing="1" cellpadding="4"> |
| |
| <tr> |
| |
| <th colspan="1" rowspan="1">Parameter</th> |
| <th colspan="1" rowspan="1">Value</th> |
| <th colspan="1" rowspan="1">Notes</th> |
| |
| </tr> |
| |
| <tr> |
| |
| <td colspan="1" rowspan="1">fs.default.name</td> |
| <td colspan="1" rowspan="1">Hostname or IP address of <span class="codefrag">NameNode</span>.</td> |
| <td colspan="1" rowspan="1"><em>host:port</em> pair.</td> |
| |
| </tr> |
| |
| <tr> |
| |
| <td colspan="1" rowspan="1">mapred.job.tracker</td> |
| <td colspan="1" rowspan="1">Hostname or IP address of <span class="codefrag">JobTracker</span>.</td> |
| <td colspan="1" rowspan="1"><em>host:port</em> pair.</td> |
| |
| </tr> |
| |
| <tr> |
| |
| <td colspan="1" rowspan="1">dfs.name.dir</td> |
| <td colspan="1" rowspan="1"> |
| Path on the local filesystem where the <span class="codefrag">NameNode</span> |
| stores the namespace and transactions logs persistently.</td> |
| <td colspan="1" rowspan="1"> |
| If this is a comma-delimited list of directories then the name |
| table is replicated in all of the directories, for redundancy. |
| </td> |
| |
| </tr> |
| |
| <tr> |
| |
| <td colspan="1" rowspan="1">dfs.data.dir</td> |
| <td colspan="1" rowspan="1"> |
| Comma separated list of paths on the local filesystem of a |
| <span class="codefrag">DataNode</span> where it should store its blocks. |
| </td> |
| <td colspan="1" rowspan="1"> |
| If this is a comma-delimited list of directories, then data will |
| be stored in all named directories, typically on different |
| devices. |
| </td> |
| |
| </tr> |
| |
| <tr> |
| |
| <td colspan="1" rowspan="1">mapred.system.dir</td> |
| <td colspan="1" rowspan="1"> |
| Path on the HDFS where where the Map-Reduce framework stores |
| system files e.g. <span class="codefrag">/hadoop/mapred/system/</span>. |
| </td> |
| <td colspan="1" rowspan="1"> |
| This is in the default filesystem (HDFS) and must be accessible |
| from both the server and client machines. |
| </td> |
| |
| </tr> |
| |
| <tr> |
| |
| <td colspan="1" rowspan="1">mapred.local.dir</td> |
| <td colspan="1" rowspan="1"> |
| Comma-separated list of paths on the local filesystem where |
| temporary Map-Reduce data is written. |
| </td> |
| <td colspan="1" rowspan="1">Multiple paths help spread disk i/o.</td> |
| |
| </tr> |
| |
| <tr> |
| |
| <td colspan="1" rowspan="1">mapred.tasktracker.{map|reduce}.tasks.maximum</td> |
| <td colspan="1" rowspan="1"> |
| The maximum number of map/reduce tasks, which are run |
| simultaneously on a given <span class="codefrag">TaskTracker</span>, individually. |
| </td> |
| <td colspan="1" rowspan="1"> |
| Defaults to 2 (2 maps and 2 reduces), but vary it depending on |
| your hardware. |
| </td> |
| |
| </tr> |
| |
| <tr> |
| |
| <td colspan="1" rowspan="1">dfs.hosts/dfs.hosts.exclude</td> |
| <td colspan="1" rowspan="1">List of permitted/excluded DataNodes.</td> |
| <td colspan="1" rowspan="1"> |
| If necessary, use these files to control the list of allowable |
| datanodes. |
| </td> |
| |
| </tr> |
| |
| <tr> |
| |
| <td colspan="1" rowspan="1">mapred.hosts/mapred.hosts.exclude</td> |
| <td colspan="1" rowspan="1">List of permitted/excluded TaskTrackers.</td> |
| <td colspan="1" rowspan="1"> |
| If necessary, use these files to control the list of allowable |
| tasktrackers. |
| </td> |
| |
| </tr> |
| |
| </table> |
| <p>Typically all the above parameters are marked as |
| <a href="api/org/apache/hadoop/conf/Configuration.html#FinalParams"> |
| final</a> to ensure that they cannot be overriden by user-applications. |
| </p> |
| <a name="N101BD"></a><a name="Real-World+Cluster+Configurations"></a> |
| <h5>Real-World Cluster Configurations</h5> |
| <p>This section lists some non-default configuration parameters which |
| have been used to run the <em>sort</em> benchmark on very large |
| clusters.</p> |
| <ul> |
| |
| <li> |
| |
| <p>Some non-default configuration values used to run sort900, |
| that is 9TB of data sorted on a cluster with 900 nodes:</p> |
| |
| <table class="ForrestTable" cellspacing="1" cellpadding="4"> |
| |
| <tr> |
| |
| <th colspan="1" rowspan="1">Parameter</th> |
| <th colspan="1" rowspan="1">Value</th> |
| <th colspan="1" rowspan="1">Notes</th> |
| |
| </tr> |
| |
| <tr> |
| |
| <td colspan="1" rowspan="1">dfs.block.size</td> |
| <td colspan="1" rowspan="1">134217728</td> |
| <td colspan="1" rowspan="1">HDFS blocksize of 128MB for large file-systems.</td> |
| |
| </tr> |
| |
| <tr> |
| |
| <td colspan="1" rowspan="1">dfs.namenode.handler.count</td> |
| <td colspan="1" rowspan="1">40</td> |
| <td colspan="1" rowspan="1"> |
| More NameNode server threads to handle RPCs from large |
| number of DataNodes. |
| </td> |
| |
| </tr> |
| |
| <tr> |
| |
| <td colspan="1" rowspan="1">mapred.reduce.parallel.copies</td> |
| <td colspan="1" rowspan="1">20</td> |
| <td colspan="1" rowspan="1"> |
| Higher number of parallel copies run by reduces to fetch |
| outputs from very large number of maps. |
| </td> |
| |
| </tr> |
| |
| <tr> |
| |
| <td colspan="1" rowspan="1">mapred.child.java.opts</td> |
| <td colspan="1" rowspan="1">-Xmx512M</td> |
| <td colspan="1" rowspan="1"> |
| Larger heap-size for child jvms of maps/reduces. |
| </td> |
| |
| </tr> |
| |
| <tr> |
| |
| <td colspan="1" rowspan="1">fs.inmemory.size.mb</td> |
| <td colspan="1" rowspan="1">200</td> |
| <td colspan="1" rowspan="1"> |
| Larger amount of memory allocated for the in-memory |
| file-system used to merge map-outputs at the reduces. |
| </td> |
| |
| </tr> |
| |
| <tr> |
| |
| <td colspan="1" rowspan="1">io.sort.factor</td> |
| <td colspan="1" rowspan="1">100</td> |
| <td colspan="1" rowspan="1">More streams merged at once while sorting files.</td> |
| |
| </tr> |
| |
| <tr> |
| |
| <td colspan="1" rowspan="1">io.sort.mb</td> |
| <td colspan="1" rowspan="1">200</td> |
| <td colspan="1" rowspan="1">Higher memory-limit while sorting data.</td> |
| |
| </tr> |
| |
| <tr> |
| |
| <td colspan="1" rowspan="1">io.file.buffer.size</td> |
| <td colspan="1" rowspan="1">131072</td> |
| <td colspan="1" rowspan="1">Size of read/write buffer used in SequenceFiles.</td> |
| |
| </tr> |
| |
| </table> |
| |
| </li> |
| |
| <li> |
| |
| <p>Updates to some configuration values to run sort1400 and |
| sort2000, that is 14TB of data sorted on 1400 nodes and 20TB of |
| data sorted on 2000 nodes:</p> |
| |
| <table class="ForrestTable" cellspacing="1" cellpadding="4"> |
| |
| <tr> |
| |
| <th colspan="1" rowspan="1">Parameter</th> |
| <th colspan="1" rowspan="1">Value</th> |
| <th colspan="1" rowspan="1">Notes</th> |
| |
| </tr> |
| |
| <tr> |
| |
| <td colspan="1" rowspan="1">mapred.job.tracker.handler.count</td> |
| <td colspan="1" rowspan="1">60</td> |
| <td colspan="1" rowspan="1"> |
| More JobTracker server threads to handle RPCs from large |
| number of TaskTrackers. |
| </td> |
| |
| </tr> |
| |
| <tr> |
| |
| <td colspan="1" rowspan="1">mapred.reduce.parallel.copies</td> |
| <td colspan="1" rowspan="1">50</td> |
| <td colspan="1" rowspan="1"></td> |
| |
| </tr> |
| |
| <tr> |
| |
| <td colspan="1" rowspan="1">tasktracker.http.threads</td> |
| <td colspan="1" rowspan="1">50</td> |
| <td colspan="1" rowspan="1"> |
| More worker threads for the TaskTracker's http server. The |
| http server is used by reduces to fetch intermediate |
| map-outputs. |
| </td> |
| |
| </tr> |
| |
| <tr> |
| |
| <td colspan="1" rowspan="1">mapred.child.java.opts</td> |
| <td colspan="1" rowspan="1">-Xmx1024M</td> |
| <td colspan="1" rowspan="1"></td> |
| |
| </tr> |
| |
| </table> |
| |
| </li> |
| |
| </ul> |
| <a name="N102DA"></a><a name="Slaves"></a> |
| <h4>Slaves</h4> |
| <p>Typically you choose one machine in the cluster to act as the |
| <span class="codefrag">NameNode</span> and one machine as to act as the |
| <span class="codefrag">JobTracker</span>, exclusively. The rest of the machines act as |
| both a <span class="codefrag">DataNode</span> and <span class="codefrag">TaskTracker</span> and are |
| referred to as <em>slaves</em>.</p> |
| <p>List all slave hostnames or IP addresses in your |
| <span class="codefrag">conf/slaves</span> file, one per line.</p> |
| <a name="N102F9"></a><a name="Logging"></a> |
| <h4>Logging</h4> |
| <p>Hadoop uses the <a href="http://logging.apache.org/log4j/">Apache |
| log4j</a> via the <a href="http://commons.apache.org/logging/">Apache |
| Commons Logging</a> framework for logging. Edit the |
| <span class="codefrag">conf/log4j.properties</span> file to customize the Hadoop |
| daemons' logging configuration (log-formats and so on).</p> |
| <a name="N1030D"></a><a name="History+Logging"></a> |
| <h5>History Logging</h5> |
| <p> The job history files are stored in central location |
| <span class="codefrag"> hadoop.job.history.location </span> which can be on DFS also, |
| whose default value is <span class="codefrag">${HADOOP_LOG_DIR}/history</span>. |
| The history web UI is accessible from job tracker web UI.</p> |
| <p> The history files are also logged to user specified directory |
| <span class="codefrag">hadoop.job.history.user.location</span> |
| which defaults to job output directory. The files are stored in |
| "_logs/history/" in the specified directory. Hence, by default |
| they will be in "mapred.output.dir/_logs/history/". User can stop |
| logging by giving the value <span class="codefrag">none</span> for |
| <span class="codefrag">hadoop.job.history.user.location</span> |
| </p> |
| <p> User can view the history logs summary in specified directory |
| using the following command <br> |
| |
| <span class="codefrag">$ bin/hadoop job -history output-dir</span> |
| <br> |
| This command will print job details, failed and killed tip |
| details. <br> |
| More details about the job such as successful tasks and |
| task attempts made for each task can be viewed using the |
| following command <br> |
| |
| <span class="codefrag">$ bin/hadoop job -history all output-dir</span> |
| <br> |
| </p> |
| <p>Once all the necessary configuration is complete, distribute the files |
| to the <span class="codefrag">HADOOP_CONF_DIR</span> directory on all the machines, |
| typically <span class="codefrag">${HADOOP_HOME}/conf</span>.</p> |
| </div> |
| |
| |
| <a name="N10345"></a><a name="Hadoop+Rack+Awareness"></a> |
| <h2 class="h3">Hadoop Rack Awareness</h2> |
| <div class="section"> |
| <p>The HDFS and the Map-Reduce components are rack-aware.</p> |
| <p>The <span class="codefrag">NameNode</span> and the <span class="codefrag">JobTracker</span> obtains the |
| <span class="codefrag">rack id</span> of the slaves in the cluster by invoking an API |
| <a href="api/org/apache/hadoop/net/DNSToSwitchMapping.html#resolve(java.util.List)">resolve</a> in an administrator configured |
| module. The API resolves the slave's DNS name (also IP address) to a |
| rack id. What module to use can be configured using the configuration |
| item <span class="codefrag">topology.node.switch.mapping.impl</span>. The default |
| implementation of the same runs a script/command configured using |
| <span class="codefrag">topology.script.file.name</span>. If topology.script.file.name is |
| not set, the rack id <span class="codefrag">/default-rack</span> is returned for any |
| passed IP address. The additional configuration in the Map-Reduce |
| part is <span class="codefrag">mapred.cache.task.levels</span> which determines the number |
| of levels (in the network topology) of caches. So, for example, if it is |
| the default value of 2, two levels of caches will be constructed - |
| one for hosts (host -> task mapping) and another for racks |
| (rack -> task mapping). |
| </p> |
| </div> |
| |
| |
| <a name="N1036B"></a><a name="Hadoop+Startup"></a> |
| <h2 class="h3">Hadoop Startup</h2> |
| <div class="section"> |
| <p>To start a Hadoop cluster you will need to start both the HDFS and |
| Map-Reduce cluster.</p> |
| <p> |
| Format a new distributed filesystem:<br> |
| |
| <span class="codefrag">$ bin/hadoop namenode -format</span> |
| |
| </p> |
| <p> |
| Start the HDFS with the following command, run on the designated |
| <span class="codefrag">NameNode</span>:<br> |
| |
| <span class="codefrag">$ bin/start-dfs.sh</span> |
| |
| </p> |
| <p>The <span class="codefrag">bin/start-dfs.sh</span> script also consults the |
| <span class="codefrag">${HADOOP_CONF_DIR}/slaves</span> file on the <span class="codefrag">NameNode</span> |
| and starts the <span class="codefrag">DataNode</span> daemon on all the listed slaves.</p> |
| <p> |
| Start Map-Reduce with the following command, run on the designated |
| <span class="codefrag">JobTracker</span>:<br> |
| |
| <span class="codefrag">$ bin/start-mapred.sh</span> |
| |
| </p> |
| <p>The <span class="codefrag">bin/start-mapred.sh</span> script also consults the |
| <span class="codefrag">${HADOOP_CONF_DIR}/slaves</span> file on the <span class="codefrag">JobTracker</span> |
| and starts the <span class="codefrag">TaskTracker</span> daemon on all the listed slaves. |
| </p> |
| </div> |
| |
| |
| <a name="N103B1"></a><a name="Hadoop+Shutdown"></a> |
| <h2 class="h3">Hadoop Shutdown</h2> |
| <div class="section"> |
| <p> |
| Stop HDFS with the following command, run on the designated |
| <span class="codefrag">NameNode</span>:<br> |
| |
| <span class="codefrag">$ bin/stop-dfs.sh</span> |
| |
| </p> |
| <p>The <span class="codefrag">bin/stop-dfs.sh</span> script also consults the |
| <span class="codefrag">${HADOOP_CONF_DIR}/slaves</span> file on the <span class="codefrag">NameNode</span> |
| and stops the <span class="codefrag">DataNode</span> daemon on all the listed slaves.</p> |
| <p> |
| Stop Map-Reduce with the following command, run on the designated |
| the designated <span class="codefrag">JobTracker</span>:<br> |
| |
| <span class="codefrag">$ bin/stop-mapred.sh</span> |
| <br> |
| |
| </p> |
| <p>The <span class="codefrag">bin/stop-mapred.sh</span> script also consults the |
| <span class="codefrag">${HADOOP_CONF_DIR}/slaves</span> file on the <span class="codefrag">JobTracker</span> |
| and stops the <span class="codefrag">TaskTracker</span> daemon on all the listed slaves.</p> |
| </div> |
| |
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