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| author | Patrick Wendell <pwendell@apache.org> | 2014-07-11 17:23:23 +0000 |
|---|---|---|
| committer | Patrick Wendell <pwendell@apache.org> | 2014-07-11 17:23:23 +0000 |
| commit | 0beac4e243f85e71554fe04093b09eb1745fea82 (patch) | |
| tree | bc20d10426c5d57e2f189305865dc2bbec447923 /site/docs/1.0.1/streaming-custom-receivers.html | |
| parent | ddec2123ba6ab95543d1b250d4f20fb811c48f09 (diff) | |
| download | spark-website-0beac4e243f85e71554fe04093b09eb1745fea82.tar.gz spark-website-0beac4e243f85e71554fe04093b09eb1745fea82.tar.bz2 spark-website-0beac4e243f85e71554fe04093b09eb1745fea82.zip | |
Updating docs for 1.0.1 release
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This guide walks through the process of implementing a custom receiver +and using it in a Spark Streaming application.</p> + +<h3 id="implementing-a-custom-receiver">Implementing a Custom Receiver</h3> + +<p>This starts with implementing a <a href="api/scala/index.html#org.apache.spark.streaming.receiver.Receiver">Receiver</a>. +A custom receiver must extend this abstract class by implementing two methods +- <code>onStart()</code>: Things to do to start receiving data. +- <code>onStop()</code>: Things to do to stop receiving data.</p> + +<p>Note that <code>onStart()</code> and <code>onStop()</code> must not block indefinitely. Typically, onStart() would start the threads +that responsible for receiving the data and <code>onStop()</code> would ensure that the receiving by those threads +are stopped. The receiving threads can also use <code>isStopped()</code>, a <code>Receiver</code> method, to check whether they +should stop receiving data.</p> + +<p>Once the data is received, that data can be stored inside Spark +by calling <code>store(data)</code>, which is a method provided by the +<a href="api/scala/index.html#org.apache.spark.streaming.receiver.Receiver">Receiver</a> class. +There are number of flavours of <code>store()</code> which allow you store the received data +record-at-a-time or as whole collection of objects / serialized bytes.</p> + +<p>Any exception in the receiving threads should be caught and handled properly to avoid silent +failures of the receiver. <code>restart(<exception>)</code> will restart the receiver by +asynchronously calling <code>onStop()</code> and then calling <code>onStart()</code> after a delay. +<code>stop(<exception>)</code> will call <code>onStop()</code> and terminate the receiver. Also, <code>reportError(<error>)</code> +reports a error message to the driver (visible in the logs and UI) without stopping / restarting +the receiver.</p> + +<p>The following is a custom receiver that receives a stream of text over a socket. It treats +‘\n’ delimited lines in the text stream as records and stores them with Spark. If the receiving thread +has any error connecting or receiving, the receiver is restarted to make another attempt to connect.</p> + +<div class="codetabs"> +<div data-lang="scala"> + + <div class="highlight"><pre><code class="scala"><span class="k">class</span> <span class="nc">CustomReceiver</span><span class="o">(</span><span class="n">host</span><span class="k">:</span> <span class="kt">String</span><span class="o">,</span> <span class="n">port</span><span class="k">:</span> <span class="kt">Int</span><span class="o">)</span> + <span class="k">extends</span> <span class="nc">Receiver</span><span class="o">[</span><span class="kt">String</span><span class="o">](</span><span class="nc">StorageLevel</span><span class="o">.</span><span class="nc">MEMORY_AND_DISK_2</span><span class="o">)</span> <span class="k">with</span> <span class="nc">Logging</span> <span class="o">{</span> + + <span class="k">def</span> <span class="n">onStart</span><span class="o">()</span> <span class="o">{</span> + <span class="c1">// Start the thread that receives data over a connection</span> + <span class="k">new</span> <span class="nc">Thread</span><span class="o">(</span><span class="s">"Socket Receiver"</span><span class="o">)</span> <span class="o">{</span> + <span class="k">override</span> <span class="k">def</span> <span class="n">run</span><span class="o">()</span> <span class="o">{</span> <span class="n">receive</span><span class="o">()</span> <span class="o">}</span> + <span class="o">}.</span><span class="n">start</span><span class="o">()</span> + <span class="o">}</span> + + <span class="k">def</span> <span class="n">onStop</span><span class="o">()</span> <span class="o">{</span> + <span class="c1">// There is nothing much to do as the thread calling receive()</span> + <span class="c1">// is designed to stop by itself isStopped() returns false</span> + <span class="o">}</span> + + <span class="cm">/** Create a socket connection and receive data until receiver is stopped */</span> + <span class="k">private</span> <span class="k">def</span> <span class="n">receive</span><span class="o">()</span> <span class="o">{</span> + <span class="k">var</span> <span class="n">socket</span><span class="k">:</span> <span class="kt">Socket</span> <span class="o">=</span> <span class="kc">null</span> + <span class="k">var</span> <span class="n">userInput</span><span class="k">:</span> <span class="kt">String</span> <span class="o">=</span> <span class="kc">null</span> + <span class="k">try</span> <span class="o">{</span> + <span class="c1">// Connect to host:port</span> + <span class="n">socket</span> <span class="k">=</span> <span class="k">new</span> <span class="nc">Socket</span><span class="o">(</span><span class="n">host</span><span class="o">,</span> <span class="n">port</span><span class="o">)</span> + + <span class="c1">// Until stopped or connection broken continue reading</span> + <span class="k">val</span> <span class="n">reader</span> <span class="k">=</span> <span class="k">new</span> <span class="nc">BufferedReader</span><span class="o">(</span><span class="k">new</span> <span class="nc">InputStreamReader</span><span class="o">(</span><span class="n">socket</span><span class="o">.</span><span class="n">getInputStream</span><span class="o">(),</span> <span class="s">"UTF-8"</span><span class="o">))</span> + <span class="n">userInput</span> <span class="k">=</span> <span class="n">reader</span><span class="o">.</span><span class="n">readLine</span><span class="o">()</span> + <span class="k">while</span><span class="o">(!</span><span class="n">isStopped</span> <span class="o">&&</span> <span class="n">userInput</span> <span class="o">!=</span> <span class="kc">null</span><span class="o">)</span> <span class="o">{</span> + <span class="n">store</span><span class="o">(</span><span class="n">userInput</span><span class="o">)</span> + <span class="n">userInput</span> <span class="k">=</span> <span class="n">reader</span><span class="o">.</span><span class="n">readLine</span><span class="o">()</span> + <span class="o">}</span> + <span class="n">reader</span><span class="o">.</span><span class="n">close</span><span class="o">()</span> + <span class="n">socket</span><span class="o">.</span><span class="n">close</span><span class="o">()</span> + + <span class="c1">// Restart in an attempt to connect again when server is active again</span> + <span class="n">restart</span><span class="o">(</span><span class="s">"Trying to connect again"</span><span class="o">)</span> + <span class="o">}</span> <span class="k">catch</span> <span class="o">{</span> + <span class="k">case</span> <span class="n">e</span><span class="k">:</span> <span class="kt">java.net.ConnectException</span> <span class="o">=></span> + <span class="c1">// restart if could not connect to server</span> + <span class="n">restart</span><span class="o">(</span><span class="s">"Error connecting to "</span> <span class="o">+</span> <span class="n">host</span> <span class="o">+</span> <span class="s">":"</span> <span class="o">+</span> <span class="n">port</span><span class="o">,</span> <span class="n">e</span><span class="o">)</span> + <span class="k">case</span> <span class="n">t</span><span class="k">:</span> <span class="kt">Throwable</span> <span class="o">=></span> + <span class="c1">// restart if there is any other error</span> + <span class="n">restart</span><span class="o">(</span><span class="s">"Error receiving data"</span><span class="o">,</span> <span class="n">t</span><span class="o">)</span> + <span class="o">}</span> + <span class="o">}</span> +<span class="o">}</span> +</code></pre></div> + + </div> +<div data-lang="java"> + + <div class="highlight"><pre><code class="java"><span class="kd">public</span> <span class="kd">class</span> <span class="nc">JavaCustomReceiver</span> <span class="kd">extends</span> <span class="n">Receiver</span><span class="o"><</span><span class="n">String</span><span class="o">></span> <span class="o">{</span> + + <span class="n">String</span> <span class="n">host</span> <span class="o">=</span> <span class="kc">null</span><span class="o">;</span> + <span class="kt">int</span> <span class="n">port</span> <span class="o">=</span> <span class="o">-</span><span class="mi">1</span><span class="o">;</span> + + <span class="kd">public</span> <span class="nf">JavaCustomReceiver</span><span class="o">(</span><span class="n">String</span> <span class="n">host_</span> <span class="o">,</span> <span class="kt">int</span> <span class="n">port_</span><span class="o">)</span> <span class="o">{</span> + <span class="kd">super</span><span class="o">(</span><span class="n">StorageLevel</span><span class="o">.</span><span class="na">MEMORY_AND_DISK_2</span><span class="o">());</span> + <span class="n">host</span> <span class="o">=</span> <span class="n">host_</span><span class="o">;</span> + <span class="n">port</span> <span class="o">=</span> <span class="n">port_</span><span class="o">;</span> + <span class="o">}</span> + + <span class="kd">public</span> <span class="kt">void</span> <span class="nf">onStart</span><span class="o">()</span> <span class="o">{</span> + <span class="c1">// Start the thread that receives data over a connection</span> + <span class="k">new</span> <span class="nf">Thread</span><span class="o">()</span> <span class="o">{</span> + <span class="nd">@Override</span> <span class="kd">public</span> <span class="kt">void</span> <span class="n">run</span><span class="o">()</span> <span class="o">{</span> + <span class="n">receive</span><span class="o">();</span> + <span class="o">}</span> + <span class="o">}.</span><span class="na">start</span><span class="o">();</span> + <span class="o">}</span> + + <span class="kd">public</span> <span class="kt">void</span> <span class="nf">onStop</span><span class="o">()</span> <span class="o">{</span> + <span class="c1">// There is nothing much to do as the thread calling receive()</span> + <span class="c1">// is designed to stop by itself isStopped() returns false</span> + <span class="o">}</span> + + <span class="cm">/** Create a socket connection and receive data until receiver is stopped */</span> + <span class="kd">private</span> <span class="kt">void</span> <span class="nf">receive</span><span class="o">()</span> <span class="o">{</span> + <span class="n">Socket</span> <span class="n">socket</span> <span class="o">=</span> <span class="kc">null</span><span class="o">;</span> + <span class="n">String</span> <span class="n">userInput</span> <span class="o">=</span> <span class="kc">null</span><span class="o">;</span> + + <span class="k">try</span> <span class="o">{</span> + <span class="c1">// connect to the server</span> + <span class="n">socket</span> <span class="o">=</span> <span class="k">new</span> <span class="n">Socket</span><span class="o">(</span><span class="n">host</span><span class="o">,</span> <span class="n">port</span><span class="o">);</span> + + <span class="n">BufferedReader</span> <span class="n">reader</span> <span class="o">=</span> <span class="k">new</span> <span class="n">BufferedReader</span><span class="o">(</span><span class="k">new</span> <span class="n">InputStreamReader</span><span class="o">(</span><span class="n">socket</span><span class="o">.</span><span class="na">getInputStream</span><span class="o">()));</span> + + <span class="c1">// Until stopped or connection broken continue reading</span> + <span class="k">while</span> <span class="o">(!</span><span class="n">isStopped</span><span class="o">()</span> <span class="o">&&</span> <span class="o">(</span><span class="n">userInput</span> <span class="o">=</span> <span class="n">reader</span><span class="o">.</span><span class="na">readLine</span><span class="o">())</span> <span class="o">!=</span> <span class="kc">null</span><span class="o">)</span> <span class="o">{</span> + <span class="n">System</span><span class="o">.</span><span class="na">out</span><span class="o">.</span><span class="na">println</span><span class="o">(</span><span class="s">"Received data '"</span> <span class="o">+</span> <span class="n">userInput</span> <span class="o">+</span> <span class="s">"'"</span><span class="o">);</span> + <span class="n">store</span><span class="o">(</span><span class="n">userInput</span><span class="o">);</span> + <span class="o">}</span> + <span class="n">reader</span><span class="o">.</span><span class="na">close</span><span class="o">();</span> + <span class="n">socket</span><span class="o">.</span><span class="na">close</span><span class="o">();</span> + + <span class="c1">// Restart in an attempt to connect again when server is active again</span> + <span class="n">restart</span><span class="o">(</span><span class="s">"Trying to connect again"</span><span class="o">);</span> + <span class="o">}</span> <span class="k">catch</span><span class="o">(</span><span class="n">ConnectException</span> <span class="n">ce</span><span class="o">)</span> <span class="o">{</span> + <span class="c1">// restart if could not connect to server</span> + <span class="n">restart</span><span class="o">(</span><span class="s">"Could not connect"</span><span class="o">,</span> <span class="n">ce</span><span class="o">);</span> + <span class="o">}</span> <span class="k">catch</span><span class="o">(</span><span class="n">Throwable</span> <span class="n">t</span><span class="o">)</span> <span class="o">{</span> + <span class="c1">// restart if there is any other error</span> + <span class="n">restart</span><span class="o">(</span><span class="s">"Error receiving data"</span><span class="o">,</span> <span class="n">t</span><span class="o">);</span> + <span class="o">}</span> + <span class="o">}</span> +<span class="o">}</span> +</code></pre></div> + + </div> +</div> + +<h3 id="using-the-custom-receiver-in-a-spark-streaming-application">Using the custom receiver in a Spark Streaming application</h3> + +<p>The custom receiver can be used in a Spark Streaming application by using +<code>streamingContext.receiverStream(<instance of custom receiver>)</code>. This will create +input DStream using data received by the instance of custom receiver, as shown below</p> + +<div class="codetabs"> +<div data-lang="scala"> + + <div class="highlight"><pre><code class="scala"><span class="c1">// Assuming ssc is the StreamingContext</span> +<span class="k">val</span> <span class="n">customReceiverStream</span> <span class="k">=</span> <span class="n">ssc</span><span class="o">.</span><span class="n">receiverStream</span><span class="o">(</span><span class="k">new</span> <span class="nc">CustomReceiver</span><span class="o">(</span><span class="n">host</span><span class="o">,</span> <span class="n">port</span><span class="o">))</span> +<span class="k">val</span> <span class="n">words</span> <span class="k">=</span> <span class="n">lines</span><span class="o">.</span><span class="n">flatMap</span><span class="o">(</span><span class="k">_</span><span class="o">.</span><span class="n">split</span><span class="o">(</span><span class="s">" "</span><span class="o">))</span> +<span class="o">...</span> +</code></pre></div> + + <p>The full source code is in the example <a href="https://github.com/apache/spark/blob/master/examples/src/main/scala/org/apache/spark/streaming/examples/CustomReceiver.scala">CustomReceiver.scala</a>.</p> + + </div> +<div data-lang="java"> + + <div class="highlight"><pre><code class="java"><span class="c1">// Assuming ssc is the JavaStreamingContext</span> +<span class="n">JavaDStream</span><span class="o"><</span><span class="n">String</span><span class="o">></span> <span class="n">customReceiverStream</span> <span class="o">=</span> <span class="n">ssc</span><span class="o">.</span><span class="na">receiverStream</span><span class="o">(</span><span class="k">new</span> <span class="n">JavaCustomReceiver</span><span class="o">(</span><span class="n">host</span><span class="o">,</span> <span class="n">port</span><span class="o">));</span> +<span class="n">JavaDStream</span><span class="o"><</span><span class="n">String</span><span class="o">></span> <span class="n">words</span> <span class="o">=</span> <span class="n">lines</span><span class="o">.</span><span class="na">flatMap</span><span class="o">(</span><span class="k">new</span> <span class="n">FlatMapFunction</span><span class="o"><</span><span class="n">String</span><span class="o">,</span> <span class="n">String</span><span class="o">>()</span> <span class="o">{</span> <span class="o">...</span> <span class="o">});</span> +<span class="o">...</span> +</code></pre></div> + + <p>The full source code is in the example <a href="https://github.com/apache/spark/blob/master/examples/src/main/java/org/apache/spark/streaming/examples/JavaCustomReceiver.java">JavaCustomReceiver.java</a>.</p> + + </div> +</div> + +<h3 id="implementing-and-using-a-custom-actor-based-receiver">Implementing and Using a Custom Actor-based Receiver</h3> + +<p>Custom <a href="http://doc.akka.io/docs/akka/2.2.4/scala/actors.html">Akka Actors</a> can also be used to +receive data. The <a href="api/scala/index.html#org.apache.spark.streaming.receiver.ActorHelper"><code>ActorHelper</code></a> +trait can be applied on any Akka actor, which allows received data to be stored in Spark using + <code>store(...)</code> methods. The supervisor strategy of this actor can be configured to handle failures, etc.</p> + +<div class="highlight"><pre><code class="scala"><span class="k">class</span> <span class="nc">CustomActor</span> <span class="k">extends</span> <span class="nc">Actor</span> <span class="k">with</span> <span class="nc">ActorHelper</span> <span class="o">{</span> + <span class="k">def</span> <span class="n">receive</span> <span class="k">=</span> <span class="o">{</span> + <span class="k">case</span> <span class="n">data</span><span class="k">:</span> <span class="kt">String</span> <span class="o">=></span> <span class="n">store</span><span class="o">(</span><span class="n">data</span><span class="o">)</span> + <span class="o">}</span> +<span class="o">}</span> +</code></pre></div> + +<p>And a new input stream can be created with this custom actor as</p> + +<div class="highlight"><pre><code class="scala"><span class="c1">// Assuming ssc is the StreamingContext</span> +<span class="k">val</span> <span class="n">lines</span> <span class="k">=</span> <span class="n">ssc</span><span class="o">.</span><span class="n">actorStream</span><span class="o">[</span><span class="kt">String</span><span class="o">](</span><span class="nc">Props</span><span class="o">(</span><span class="k">new</span> <span class="nc">CustomActor</span><span class="o">()),</span> <span class="s">"CustomReceiver"</span><span class="o">)</span> +</code></pre></div> + +<p>See <a href="https://github.com/apache/spark/blob/master/examples/src/main/scala/org/apache/spark/streaming/examples/ActorWordCount.scala">ActorWordCount.scala</a> +for an end-to-end example.</p> + + + + </div> <!-- /container --> + + <script src="js/vendor/jquery-1.8.0.min.js"></script> + <script src="js/vendor/bootstrap.min.js"></script> + <script src="js/main.js"></script> + + <!-- MathJax Section --> + <script type="text/x-mathjax-config"> + MathJax.Hub.Config({ + TeX: { equationNumbers: { autoNumber: "AMS" } } + }); + </script> + <script> + // Note that we load MathJax this way to work with local file (file://), HTTP and HTTPS. + // We could use "//cdn.mathjax...", but that won't support "file://". + (function(d, script) { + script = d.createElement('script'); + script.type = 'text/javascript'; + script.async = true; + script.onload = function(){ + MathJax.Hub.Config({ + tex2jax: { + inlineMath: [ ["$", "$"], ["\\\\(","\\\\)"] ], + displayMath: [ ["$$","$$"], ["\\[", "\\]"] ], + processEscapes: true, + skipTags: ['script', 'noscript', 'style', 'textarea', 'pre'] + } + }); + }; + script.src = ('https:' == document.location.protocol ? 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