|
|
@@ -307,7 +307,7 @@ document.write("Last Published: " + document.lastModified);
|
|
|
<a href="#Example%3A+WordCount+v2.0">Example: WordCount v2.0</a>
|
|
|
<ul class="minitoc">
|
|
|
<li>
|
|
|
-<a href="#Source+Code-N10D94">Source Code</a>
|
|
|
+<a href="#Source+Code-N10DA0">Source Code</a>
|
|
|
</li>
|
|
|
<li>
|
|
|
<a href="#Sample+Runs">Sample Runs</a>
|
|
|
@@ -1547,7 +1547,17 @@ document.write("Last Published: " + document.lastModified);
|
|
|
|
|
|
</p>
|
|
|
<p>Users/admins can also specify the maximum virtual memory
|
|
|
- of the launched child-task using <span class="codefrag">mapred.child.ulimit</span>.</p>
|
|
|
+ of the launched child-task using <span class="codefrag">mapred.child.ulimit</span>.
|
|
|
+ The value for <span class="codefrag">mapred.child.ulimit</span> should be specified
|
|
|
+ in kilo bytes (KB). And also the value must be greater than
|
|
|
+ or equal to the -Xmx passed to JavaVM, else the VM might not start.
|
|
|
+ </p>
|
|
|
+<p>Note: <span class="codefrag">mapred.child.java.opts</span> are used only for
|
|
|
+ configuring the launched child tasks from task tracker. Configuring
|
|
|
+ the memory options for daemons is documented in
|
|
|
+ <a href="cluster_setup.html#Configuring+the+Environment+of+the+Hadoop+Daemons">
|
|
|
+ cluster_setup.html </a>
|
|
|
+</p>
|
|
|
<p>The task tracker has local directory,
|
|
|
<span class="codefrag"> ${mapred.local.dir}/taskTracker/</span> to create localized
|
|
|
cache and localized job. It can define multiple local directories
|
|
|
@@ -1731,7 +1741,7 @@ document.write("Last Published: " + document.lastModified);
|
|
|
loaded via <a href="http://java.sun.com/j2se/1.5.0/docs/api/java/lang/System.html#loadLibrary(java.lang.String)">
|
|
|
System.loadLibrary</a> or <a href="http://java.sun.com/j2se/1.5.0/docs/api/java/lang/System.html#load(java.lang.String)">
|
|
|
System.load</a>.</p>
|
|
|
-<a name="N109EB"></a><a name="Job+Submission+and+Monitoring"></a>
|
|
|
+<a name="N109F7"></a><a name="Job+Submission+and+Monitoring"></a>
|
|
|
<h3 class="h4">Job Submission and Monitoring</h3>
|
|
|
<p>
|
|
|
<a href="api/org/apache/hadoop/mapred/JobClient.html">
|
|
|
@@ -1792,7 +1802,7 @@ document.write("Last Published: " + document.lastModified);
|
|
|
<p>Normally the user creates the application, describes various facets
|
|
|
of the job via <span class="codefrag">JobConf</span>, and then uses the
|
|
|
<span class="codefrag">JobClient</span> to submit the job and monitor its progress.</p>
|
|
|
-<a name="N10A4B"></a><a name="Job+Control"></a>
|
|
|
+<a name="N10A57"></a><a name="Job+Control"></a>
|
|
|
<h4>Job Control</h4>
|
|
|
<p>Users may need to chain map-reduce jobs to accomplish complex
|
|
|
tasks which cannot be done via a single map-reduce job. This is fairly
|
|
|
@@ -1828,7 +1838,7 @@ document.write("Last Published: " + document.lastModified);
|
|
|
</li>
|
|
|
|
|
|
</ul>
|
|
|
-<a name="N10A75"></a><a name="Job+Input"></a>
|
|
|
+<a name="N10A81"></a><a name="Job+Input"></a>
|
|
|
<h3 class="h4">Job Input</h3>
|
|
|
<p>
|
|
|
<a href="api/org/apache/hadoop/mapred/InputFormat.html">
|
|
|
@@ -1876,7 +1886,7 @@ document.write("Last Published: " + document.lastModified);
|
|
|
appropriate <span class="codefrag">CompressionCodec</span>. However, it must be noted that
|
|
|
compressed files with the above extensions cannot be <em>split</em> and
|
|
|
each compressed file is processed in its entirety by a single mapper.</p>
|
|
|
-<a name="N10ADF"></a><a name="InputSplit"></a>
|
|
|
+<a name="N10AEB"></a><a name="InputSplit"></a>
|
|
|
<h4>InputSplit</h4>
|
|
|
<p>
|
|
|
<a href="api/org/apache/hadoop/mapred/InputSplit.html">
|
|
|
@@ -1890,7 +1900,7 @@ document.write("Last Published: " + document.lastModified);
|
|
|
FileSplit</a> is the default <span class="codefrag">InputSplit</span>. It sets
|
|
|
<span class="codefrag">map.input.file</span> to the path of the input file for the
|
|
|
logical split.</p>
|
|
|
-<a name="N10B04"></a><a name="RecordReader"></a>
|
|
|
+<a name="N10B10"></a><a name="RecordReader"></a>
|
|
|
<h4>RecordReader</h4>
|
|
|
<p>
|
|
|
<a href="api/org/apache/hadoop/mapred/RecordReader.html">
|
|
|
@@ -1902,7 +1912,7 @@ document.write("Last Published: " + document.lastModified);
|
|
|
for processing. <span class="codefrag">RecordReader</span> thus assumes the
|
|
|
responsibility of processing record boundaries and presents the tasks
|
|
|
with keys and values.</p>
|
|
|
-<a name="N10B27"></a><a name="Job+Output"></a>
|
|
|
+<a name="N10B33"></a><a name="Job+Output"></a>
|
|
|
<h3 class="h4">Job Output</h3>
|
|
|
<p>
|
|
|
<a href="api/org/apache/hadoop/mapred/OutputFormat.html">
|
|
|
@@ -1927,7 +1937,7 @@ document.write("Last Published: " + document.lastModified);
|
|
|
<p>
|
|
|
<span class="codefrag">TextOutputFormat</span> is the default
|
|
|
<span class="codefrag">OutputFormat</span>.</p>
|
|
|
-<a name="N10B50"></a><a name="Task+Side-Effect+Files"></a>
|
|
|
+<a name="N10B5C"></a><a name="Task+Side-Effect+Files"></a>
|
|
|
<h4>Task Side-Effect Files</h4>
|
|
|
<p>In some applications, component tasks need to create and/or write to
|
|
|
side-files, which differ from the actual job-output files.</p>
|
|
|
@@ -1966,7 +1976,7 @@ document.write("Last Published: " + document.lastModified);
|
|
|
<p>The entire discussion holds true for maps of jobs with
|
|
|
reducer=NONE (i.e. 0 reduces) since output of the map, in that case,
|
|
|
goes directly to HDFS.</p>
|
|
|
-<a name="N10B98"></a><a name="RecordWriter"></a>
|
|
|
+<a name="N10BA4"></a><a name="RecordWriter"></a>
|
|
|
<h4>RecordWriter</h4>
|
|
|
<p>
|
|
|
<a href="api/org/apache/hadoop/mapred/RecordWriter.html">
|
|
|
@@ -1974,9 +1984,9 @@ document.write("Last Published: " + document.lastModified);
|
|
|
pairs to an output file.</p>
|
|
|
<p>RecordWriter implementations write the job outputs to the
|
|
|
<span class="codefrag">FileSystem</span>.</p>
|
|
|
-<a name="N10BAF"></a><a name="Other+Useful+Features"></a>
|
|
|
+<a name="N10BBB"></a><a name="Other+Useful+Features"></a>
|
|
|
<h3 class="h4">Other Useful Features</h3>
|
|
|
-<a name="N10BB5"></a><a name="Counters"></a>
|
|
|
+<a name="N10BC1"></a><a name="Counters"></a>
|
|
|
<h4>Counters</h4>
|
|
|
<p>
|
|
|
<span class="codefrag">Counters</span> represent global counters, defined either by
|
|
|
@@ -1990,7 +2000,7 @@ document.write("Last Published: " + document.lastModified);
|
|
|
Reporter.incrCounter(Enum, long)</a> in the <span class="codefrag">map</span> and/or
|
|
|
<span class="codefrag">reduce</span> methods. These counters are then globally
|
|
|
aggregated by the framework.</p>
|
|
|
-<a name="N10BE0"></a><a name="DistributedCache"></a>
|
|
|
+<a name="N10BEC"></a><a name="DistributedCache"></a>
|
|
|
<h4>DistributedCache</h4>
|
|
|
<p>
|
|
|
<a href="api/org/apache/hadoop/filecache/DistributedCache.html">
|
|
|
@@ -2024,7 +2034,7 @@ document.write("Last Published: " + document.lastModified);
|
|
|
<a href="api/org/apache/hadoop/filecache/DistributedCache.html#createSymlink(org.apache.hadoop.conf.Configuration)">
|
|
|
DistributedCache.createSymlink(Configuration)</a> api. Files
|
|
|
have <em>execution permissions</em> set.</p>
|
|
|
-<a name="N10C1E"></a><a name="Tool"></a>
|
|
|
+<a name="N10C2A"></a><a name="Tool"></a>
|
|
|
<h4>Tool</h4>
|
|
|
<p>The <a href="api/org/apache/hadoop/util/Tool.html">Tool</a>
|
|
|
interface supports the handling of generic Hadoop command-line options.
|
|
|
@@ -2064,7 +2074,7 @@ document.write("Last Published: " + document.lastModified);
|
|
|
</span>
|
|
|
|
|
|
</p>
|
|
|
-<a name="N10C50"></a><a name="IsolationRunner"></a>
|
|
|
+<a name="N10C5C"></a><a name="IsolationRunner"></a>
|
|
|
<h4>IsolationRunner</h4>
|
|
|
<p>
|
|
|
<a href="api/org/apache/hadoop/mapred/IsolationRunner.html">
|
|
|
@@ -2088,7 +2098,7 @@ document.write("Last Published: " + document.lastModified);
|
|
|
<p>
|
|
|
<span class="codefrag">IsolationRunner</span> will run the failed task in a single
|
|
|
jvm, which can be in the debugger, over precisely the same input.</p>
|
|
|
-<a name="N10C83"></a><a name="Profiling"></a>
|
|
|
+<a name="N10C8F"></a><a name="Profiling"></a>
|
|
|
<h4>Profiling</h4>
|
|
|
<p>Profiling is a utility to get a representative (2 or 3) sample
|
|
|
of built-in java profiler for a sample of maps and reduces. </p>
|
|
|
@@ -2121,7 +2131,7 @@ document.write("Last Published: " + document.lastModified);
|
|
|
<span class="codefrag">-agentlib:hprof=cpu=samples,heap=sites,force=n,thread=y,verbose=n,file=%s</span>
|
|
|
|
|
|
</p>
|
|
|
-<a name="N10CB7"></a><a name="Debugging"></a>
|
|
|
+<a name="N10CC3"></a><a name="Debugging"></a>
|
|
|
<h4>Debugging</h4>
|
|
|
<p>Map/Reduce framework provides a facility to run user-provided
|
|
|
scripts for debugging. When map/reduce task fails, user can run
|
|
|
@@ -2132,7 +2142,7 @@ document.write("Last Published: " + document.lastModified);
|
|
|
<p> In the following sections we discuss how to submit debug script
|
|
|
along with the job. For submitting debug script, first it has to
|
|
|
distributed. Then the script has to supplied in Configuration. </p>
|
|
|
-<a name="N10CC3"></a><a name="How+to+distribute+script+file%3A"></a>
|
|
|
+<a name="N10CCF"></a><a name="How+to+distribute+script+file%3A"></a>
|
|
|
<h5> How to distribute script file: </h5>
|
|
|
<p>
|
|
|
To distribute the debug script file, first copy the file to the dfs.
|
|
|
@@ -2155,7 +2165,7 @@ document.write("Last Published: " + document.lastModified);
|
|
|
<a href="api/org/apache/hadoop/filecache/DistributedCache.html#createSymlink(org.apache.hadoop.conf.Configuration)">
|
|
|
DistributedCache.createSymLink(Configuration) </a> api.
|
|
|
</p>
|
|
|
-<a name="N10CDC"></a><a name="How+to+submit+script%3A"></a>
|
|
|
+<a name="N10CE8"></a><a name="How+to+submit+script%3A"></a>
|
|
|
<h5> How to submit script: </h5>
|
|
|
<p> A quick way to submit debug script is to set values for the
|
|
|
properties "mapred.map.task.debug.script" and
|
|
|
@@ -2179,17 +2189,17 @@ document.write("Last Published: " + document.lastModified);
|
|
|
<span class="codefrag">$script $stdout $stderr $syslog $jobconf $program </span>
|
|
|
|
|
|
</p>
|
|
|
-<a name="N10CFE"></a><a name="Default+Behavior%3A"></a>
|
|
|
+<a name="N10D0A"></a><a name="Default+Behavior%3A"></a>
|
|
|
<h5> Default Behavior: </h5>
|
|
|
<p> For pipes, a default script is run to process core dumps under
|
|
|
gdb, prints stack trace and gives info about running threads. </p>
|
|
|
-<a name="N10D09"></a><a name="JobControl"></a>
|
|
|
+<a name="N10D15"></a><a name="JobControl"></a>
|
|
|
<h4>JobControl</h4>
|
|
|
<p>
|
|
|
<a href="api/org/apache/hadoop/mapred/jobcontrol/package-summary.html">
|
|
|
JobControl</a> is a utility which encapsulates a set of Map-Reduce jobs
|
|
|
and their dependencies.</p>
|
|
|
-<a name="N10D16"></a><a name="Data+Compression"></a>
|
|
|
+<a name="N10D22"></a><a name="Data+Compression"></a>
|
|
|
<h4>Data Compression</h4>
|
|
|
<p>Hadoop Map-Reduce provides facilities for the application-writer to
|
|
|
specify compression for both intermediate map-outputs and the
|
|
|
@@ -2203,7 +2213,7 @@ document.write("Last Published: " + document.lastModified);
|
|
|
codecs for reasons of both performance (zlib) and non-availability of
|
|
|
Java libraries (lzo). More details on their usage and availability are
|
|
|
available <a href="native_libraries.html">here</a>.</p>
|
|
|
-<a name="N10D36"></a><a name="Intermediate+Outputs"></a>
|
|
|
+<a name="N10D42"></a><a name="Intermediate+Outputs"></a>
|
|
|
<h5>Intermediate Outputs</h5>
|
|
|
<p>Applications can control compression of intermediate map-outputs
|
|
|
via the
|
|
|
@@ -2212,7 +2222,7 @@ document.write("Last Published: " + document.lastModified);
|
|
|
<span class="codefrag">CompressionCodec</span> to be used via the
|
|
|
<a href="api/org/apache/hadoop/mapred/JobConf.html#setMapOutputCompressorClass(java.lang.Class)">
|
|
|
JobConf.setMapOutputCompressorClass(Class)</a> api.</p>
|
|
|
-<a name="N10D4B"></a><a name="Job+Outputs"></a>
|
|
|
+<a name="N10D57"></a><a name="Job+Outputs"></a>
|
|
|
<h5>Job Outputs</h5>
|
|
|
<p>Applications can control compression of job-outputs via the
|
|
|
<a href="api/org/apache/hadoop/mapred/OutputFormatBase.html#setCompressOutput(org.apache.hadoop.mapred.JobConf,%20boolean)">
|
|
|
@@ -2232,7 +2242,7 @@ document.write("Last Published: " + document.lastModified);
|
|
|
</div>
|
|
|
|
|
|
|
|
|
-<a name="N10D7A"></a><a name="Example%3A+WordCount+v2.0"></a>
|
|
|
+<a name="N10D86"></a><a name="Example%3A+WordCount+v2.0"></a>
|
|
|
<h2 class="h3">Example: WordCount v2.0</h2>
|
|
|
<div class="section">
|
|
|
<p>Here is a more complete <span class="codefrag">WordCount</span> which uses many of the
|
|
|
@@ -2242,7 +2252,7 @@ document.write("Last Published: " + document.lastModified);
|
|
|
<a href="quickstart.html#SingleNodeSetup">pseudo-distributed</a> or
|
|
|
<a href="quickstart.html#Fully-Distributed+Operation">fully-distributed</a>
|
|
|
Hadoop installation.</p>
|
|
|
-<a name="N10D94"></a><a name="Source+Code-N10D94"></a>
|
|
|
+<a name="N10DA0"></a><a name="Source+Code-N10DA0"></a>
|
|
|
<h3 class="h4">Source Code</h3>
|
|
|
<table class="ForrestTable" cellspacing="1" cellpadding="4">
|
|
|
|
|
|
@@ -3452,7 +3462,7 @@ document.write("Last Published: " + document.lastModified);
|
|
|
</tr>
|
|
|
|
|
|
</table>
|
|
|
-<a name="N114F6"></a><a name="Sample+Runs"></a>
|
|
|
+<a name="N11502"></a><a name="Sample+Runs"></a>
|
|
|
<h3 class="h4">Sample Runs</h3>
|
|
|
<p>Sample text-files as input:</p>
|
|
|
<p>
|
|
|
@@ -3620,7 +3630,7 @@ document.write("Last Published: " + document.lastModified);
|
|
|
<br>
|
|
|
|
|
|
</p>
|
|
|
-<a name="N115CA"></a><a name="Highlights"></a>
|
|
|
+<a name="N115D6"></a><a name="Highlights"></a>
|
|
|
<h3 class="h4">Highlights</h3>
|
|
|
<p>The second version of <span class="codefrag">WordCount</span> improves upon the
|
|
|
previous one by using some features offered by the Map-Reduce framework:
|
Devaraj Das