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Posted to commits@storm.apache.org by pt...@apache.org on 2018/02/15 22:04:12 UTC
[05/51] [partial] storm-site git commit: publish 1.2.0, 1.1.2,
1.0.6 releases
http://git-wip-us.apache.org/repos/asf/storm-site/blob/d522e354/content/releases/1.0.6/Windowing.html
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+ <h1 class="page-title">Windowing Support in Core Storm</h1>
+ <div class="row">
+ <div class="col-md-12">
+ <!-- Documentation -->
+
+<p class="post-meta"></p>
+
+<p>Storm core has support for processing a group of tuples that falls within a window. Windows are specified with the
+following two parameters,</p>
+
+<ol>
+<li>Window length - the length or duration of the window</li>
+<li>Sliding interval - the interval at which the windowing slides</li>
+</ol>
+
+<h2 id="sliding-window">Sliding Window</h2>
+
+<p>Tuples are grouped in windows and window slides every sliding interval. A tuple can belong to more than one window.</p>
+
+<p>For example a time duration based sliding window with length 10 secs and sliding interval of 5 seconds.</p>
+<div class="highlight"><pre><code class="language-" data-lang="">........| e1 e2 | e3 e4 e5 e6 | e7 e8 e9 |...
+-5 0 5 10 15 -> time
+|<------- w1 -->|
+ |<---------- w2 ----->|
+ |<-------------- w3 ---->|
+</code></pre></div>
+<p>The window is evaluated every 5 seconds and some of the tuples in the first window overlaps with the second one.</p>
+
+<p>Note: The window first slides at t = 5 secs and would contain events received up to the first five secs.</p>
+
+<h2 id="tumbling-window">Tumbling Window</h2>
+
+<p>Tuples are grouped in a single window based on time or count. Any tuple belongs to only one of the windows.</p>
+
+<p>For example a time duration based tumbling window with length 5 secs.</p>
+<div class="highlight"><pre><code class="language-" data-lang="">| e1 e2 | e3 e4 e5 e6 | e7 e8 e9 |...
+0 5 10 15 -> time
+ w1 w2 w3
+</code></pre></div>
+<p>The window is evaluated every five seconds and none of the windows overlap.</p>
+
+<p>Storm supports specifying the window length and sliding intervals as a count of the number of tuples or as a time duration.</p>
+
+<p>The bolt interface <code>IWindowedBolt</code> is implemented by bolts that needs windowing support.</p>
+<div class="highlight"><pre><code class="language-java" data-lang="java"><span class="kd">public</span> <span class="kd">interface</span> <span class="nc">IWindowedBolt</span> <span class="kd">extends</span> <span class="n">IComponent</span> <span class="o">{</span>
+ <span class="kt">void</span> <span class="nf">prepare</span><span class="o">(</span><span class="n">Map</span> <span class="n">stormConf</span><span class="o">,</span> <span class="n">TopologyContext</span> <span class="n">context</span><span class="o">,</span> <span class="n">OutputCollector</span> <span class="n">collector</span><span class="o">);</span>
+ <span class="cm">/**
+ * Process tuples falling within the window and optionally emit
+ * new tuples based on the tuples in the input window.
+ */</span>
+ <span class="kt">void</span> <span class="nf">execute</span><span class="o">(</span><span class="n">TupleWindow</span> <span class="n">inputWindow</span><span class="o">);</span>
+ <span class="kt">void</span> <span class="nf">cleanup</span><span class="o">();</span>
+<span class="o">}</span>
+</code></pre></div>
+<p>Every time the window activates, the <code>execute</code> method is invoked. The TupleWindow parameter gives access to the current tuples
+in the window, the tuples that expired and the new tuples that are added since last window was computed which will be useful
+for efficient windowing computations.</p>
+
+<p>Bolts that needs windowing support typically would extend <code>BaseWindowedBolt</code> which has the apis for specifying the
+window length and sliding intervals.</p>
+
+<p>E.g. </p>
+<div class="highlight"><pre><code class="language-java" data-lang="java"><span class="kd">public</span> <span class="kd">class</span> <span class="nc">SlidingWindowBolt</span> <span class="kd">extends</span> <span class="n">BaseWindowedBolt</span> <span class="o">{</span>
+ <span class="kd">private</span> <span class="n">OutputCollector</span> <span class="n">collector</span><span class="o">;</span>
+
+ <span class="nd">@Override</span>
+ <span class="kd">public</span> <span class="kt">void</span> <span class="nf">prepare</span><span class="o">(</span><span class="n">Map</span> <span class="n">stormConf</span><span class="o">,</span> <span class="n">TopologyContext</span> <span class="n">context</span><span class="o">,</span> <span class="n">OutputCollector</span> <span class="n">collector</span><span class="o">)</span> <span class="o">{</span>
+ <span class="k">this</span><span class="o">.</span><span class="na">collector</span> <span class="o">=</span> <span class="n">collector</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="nf">execute</span><span class="o">(</span><span class="n">TupleWindow</span> <span class="n">inputWindow</span><span class="o">)</span> <span class="o">{</span>
+ <span class="k">for</span><span class="o">(</span><span class="n">Tuple</span> <span class="nl">tuple:</span> <span class="n">inputWindow</span><span class="o">.</span><span class="na">get</span><span class="o">())</span> <span class="o">{</span>
+ <span class="c1">// do the windowing computation</span>
+ <span class="o">...</span>
+ <span class="o">}</span>
+ <span class="c1">// emit the results</span>
+ <span class="n">collector</span><span class="o">.</span><span class="na">emit</span><span class="o">(</span><span class="k">new</span> <span class="n">Values</span><span class="o">(</span><span class="n">computedValue</span><span class="o">));</span>
+ <span class="o">}</span>
+<span class="o">}</span>
+
+<span class="kd">public</span> <span class="kd">static</span> <span class="kt">void</span> <span class="nf">main</span><span class="o">(</span><span class="n">String</span><span class="o">[]</span> <span class="n">args</span><span class="o">)</span> <span class="o">{</span>
+ <span class="n">TopologyBuilder</span> <span class="n">builder</span> <span class="o">=</span> <span class="k">new</span> <span class="n">TopologyBuilder</span><span class="o">();</span>
+ <span class="n">builder</span><span class="o">.</span><span class="na">setSpout</span><span class="o">(</span><span class="s">"spout"</span><span class="o">,</span> <span class="k">new</span> <span class="n">RandomSentenceSpout</span><span class="o">(),</span> <span class="mi">1</span><span class="o">);</span>
+ <span class="n">builder</span><span class="o">.</span><span class="na">setBolt</span><span class="o">(</span><span class="s">"slidingwindowbolt"</span><span class="o">,</span>
+ <span class="k">new</span> <span class="nf">SlidingWindowBolt</span><span class="o">().</span><span class="na">withWindow</span><span class="o">(</span><span class="k">new</span> <span class="n">Count</span><span class="o">(</span><span class="mi">30</span><span class="o">),</span> <span class="k">new</span> <span class="n">Count</span><span class="o">(</span><span class="mi">10</span><span class="o">)),</span>
+ <span class="mi">1</span><span class="o">).</span><span class="na">shuffleGrouping</span><span class="o">(</span><span class="s">"spout"</span><span class="o">);</span>
+ <span class="n">Config</span> <span class="n">conf</span> <span class="o">=</span> <span class="k">new</span> <span class="n">Config</span><span class="o">();</span>
+ <span class="n">conf</span><span class="o">.</span><span class="na">setDebug</span><span class="o">(</span><span class="kc">true</span><span class="o">);</span>
+ <span class="n">conf</span><span class="o">.</span><span class="na">setNumWorkers</span><span class="o">(</span><span class="mi">1</span><span class="o">);</span>
+
+ <span class="n">StormSubmitter</span><span class="o">.</span><span class="na">submitTopologyWithProgressBar</span><span class="o">(</span><span class="n">args</span><span class="o">[</span><span class="mi">0</span><span class="o">],</span> <span class="n">conf</span><span class="o">,</span> <span class="n">builder</span><span class="o">.</span><span class="na">createTopology</span><span class="o">());</span>
+
+<span class="o">}</span>
+</code></pre></div>
+<p>The following window configurations are supported.</p>
+<div class="highlight"><pre><code class="language-java" data-lang="java"><span class="n">withWindow</span><span class="o">(</span><span class="n">Count</span> <span class="n">windowLength</span><span class="o">,</span> <span class="n">Count</span> <span class="n">slidingInterval</span><span class="o">)</span>
+<span class="n">Tuple</span> <span class="n">count</span> <span class="n">based</span> <span class="n">sliding</span> <span class="n">window</span> <span class="n">that</span> <span class="n">slides</span> <span class="n">after</span> <span class="err">`</span><span class="n">slidingInterval</span><span class="err">`</span> <span class="n">number</span> <span class="n">of</span> <span class="n">tuples</span><span class="o">.</span>
+
+<span class="nf">withWindow</span><span class="o">(</span><span class="n">Count</span> <span class="n">windowLength</span><span class="o">)</span>
+<span class="n">Tuple</span> <span class="n">count</span> <span class="n">based</span> <span class="n">window</span> <span class="n">that</span> <span class="n">slides</span> <span class="n">with</span> <span class="n">every</span> <span class="n">incoming</span> <span class="n">tuple</span><span class="o">.</span>
+
+<span class="nf">withWindow</span><span class="o">(</span><span class="n">Count</span> <span class="n">windowLength</span><span class="o">,</span> <span class="n">Duration</span> <span class="n">slidingInterval</span><span class="o">)</span>
+<span class="n">Tuple</span> <span class="n">count</span> <span class="n">based</span> <span class="n">sliding</span> <span class="n">window</span> <span class="n">that</span> <span class="n">slides</span> <span class="n">after</span> <span class="err">`</span><span class="n">slidingInterval</span><span class="err">`</span> <span class="n">time</span> <span class="n">duration</span><span class="o">.</span>
+
+<span class="nf">withWindow</span><span class="o">(</span><span class="n">Duration</span> <span class="n">windowLength</span><span class="o">,</span> <span class="n">Duration</span> <span class="n">slidingInterval</span><span class="o">)</span>
+<span class="n">Time</span> <span class="n">duration</span> <span class="n">based</span> <span class="n">sliding</span> <span class="n">window</span> <span class="n">that</span> <span class="n">slides</span> <span class="n">after</span> <span class="err">`</span><span class="n">slidingInterval</span><span class="err">`</span> <span class="n">time</span> <span class="n">duration</span><span class="o">.</span>
+
+<span class="nf">withWindow</span><span class="o">(</span><span class="n">Duration</span> <span class="n">windowLength</span><span class="o">)</span>
+<span class="n">Time</span> <span class="n">duration</span> <span class="n">based</span> <span class="n">window</span> <span class="n">that</span> <span class="n">slides</span> <span class="n">with</span> <span class="n">every</span> <span class="n">incoming</span> <span class="n">tuple</span><span class="o">.</span>
+
+<span class="nf">withWindow</span><span class="o">(</span><span class="n">Duration</span> <span class="n">windowLength</span><span class="o">,</span> <span class="n">Count</span> <span class="n">slidingInterval</span><span class="o">)</span>
+<span class="n">Time</span> <span class="n">duration</span> <span class="n">based</span> <span class="n">sliding</span> <span class="n">window</span> <span class="n">configuration</span> <span class="n">that</span> <span class="n">slides</span> <span class="n">after</span> <span class="err">`</span><span class="n">slidingInterval</span><span class="err">`</span> <span class="n">number</span> <span class="n">of</span> <span class="n">tuples</span><span class="o">.</span>
+
+<span class="nf">withTumblingWindow</span><span class="o">(</span><span class="n">BaseWindowedBolt</span><span class="o">.</span><span class="na">Count</span> <span class="n">count</span><span class="o">)</span>
+<span class="n">Count</span> <span class="n">based</span> <span class="n">tumbling</span> <span class="n">window</span> <span class="n">that</span> <span class="n">tumbles</span> <span class="n">after</span> <span class="n">the</span> <span class="n">specified</span> <span class="n">count</span> <span class="n">of</span> <span class="n">tuples</span><span class="o">.</span>
+
+<span class="nf">withTumblingWindow</span><span class="o">(</span><span class="n">BaseWindowedBolt</span><span class="o">.</span><span class="na">Duration</span> <span class="n">duration</span><span class="o">)</span>
+<span class="n">Time</span> <span class="n">duration</span> <span class="n">based</span> <span class="n">tumbling</span> <span class="n">window</span> <span class="n">that</span> <span class="n">tumbles</span> <span class="n">after</span> <span class="n">the</span> <span class="n">specified</span> <span class="n">time</span> <span class="n">duration</span><span class="o">.</span>
+
+</code></pre></div>
+<h2 id="tuple-timestamp-and-out-of-order-tuples">Tuple timestamp and out of order tuples</h2>
+
+<p>By default the timestamp tracked in the window is the time when the tuple is processed by the bolt. The window calculations
+are performed based on the processing timestamp. Storm has support for tracking windows based on the source generated timestamp.</p>
+<div class="highlight"><pre><code class="language-java" data-lang="java"><span class="cm">/**
+* Specify a field in the tuple that represents the timestamp as a long value. If this
+* field is not present in the incoming tuple, an {@link IllegalArgumentException} will be thrown.
+*
+* @param fieldName the name of the field that contains the timestamp
+*/</span>
+<span class="kd">public</span> <span class="n">BaseWindowedBolt</span> <span class="nf">withTimestampField</span><span class="o">(</span><span class="n">String</span> <span class="n">fieldName</span><span class="o">)</span>
+</code></pre></div>
+<p>The value for the above <code>fieldName</code> will be looked up from the incoming tuple and considered for windowing calculations.
+If the field is not present in the tuple an exception will be thrown. Along with the timestamp field name, a time lag parameter
+can also be specified which indicates the max time limit for tuples with out of order timestamps. </p>
+
+<p>E.g. If the lag is 5 secs and a tuple <code>t1</code> arrived with timestamp <code>06:00:05</code> no tuples may arrive with tuple timestamp earlier than <code>06:00:00</code>. If a tuple
+arrives with timestamp 05:59:59 after <code>t1</code> and the window has moved past <code>t1</code>, it will be treated as a late tuple and not processed. Currently the late
+ tuples are just logged in the worker log files at INFO level.</p>
+<div class="highlight"><pre><code class="language-java" data-lang="java"><span class="cm">/**
+* Specify the maximum time lag of the tuple timestamp in milliseconds. It means that the tuple timestamps
+* cannot be out of order by more than this amount.
+*
+* @param duration the max lag duration
+*/</span>
+<span class="kd">public</span> <span class="n">BaseWindowedBolt</span> <span class="nf">withLag</span><span class="o">(</span><span class="n">Duration</span> <span class="n">duration</span><span class="o">)</span>
+</code></pre></div>
+<h3 id="watermarks">Watermarks</h3>
+
+<p>For processing tuples with timestamp field, storm internally computes watermarks based on the incoming tuple timestamp. Watermark is
+the minimum of the latest tuple timestamps (minus the lag) across all the input streams. At a higher level this is similar to the watermark concept
+used by Flink and Google's MillWheel for tracking event based timestamps.</p>
+
+<p>Periodically (default every sec), the watermark timestamps are emitted and this is considered as the clock tick for the window calculation if
+tuple based timestamps are in use. The interval at which watermarks are emitted can be changed with the below api.</p>
+<div class="highlight"><pre><code class="language-java" data-lang="java"><span class="cm">/**
+* Specify the watermark event generation interval. For tuple based timestamps, watermark events
+* are used to track the progress of time
+*
+* @param interval the interval at which watermark events are generated
+*/</span>
+<span class="kd">public</span> <span class="n">BaseWindowedBolt</span> <span class="nf">withWatermarkInterval</span><span class="o">(</span><span class="n">Duration</span> <span class="n">interval</span><span class="o">)</span>
+</code></pre></div>
+<p>When a watermark is received, all windows up to that timestamp will be evaluated.</p>
+
+<p>For example, consider tuple timestamp based processing with following window parameters,</p>
+
+<p><code>Window length = 20s, sliding interval = 10s, watermark emit frequency = 1s, max lag = 5s</code></p>
+<div class="highlight"><pre><code class="language-" data-lang="">|-----|-----|-----|-----|-----|-----|-----|
+0 10 20 30 40 50 60 70
+</code></pre></div>
+<p>Current ts = <code>09:00:00</code></p>
+
+<p>Tuples <code>e1(6:00:03), e2(6:00:05), e3(6:00:07), e4(6:00:18), e5(6:00:26), e6(6:00:36)</code> are received between <code>9:00:00</code> and <code>9:00:01</code></p>
+
+<p>At time t = <code>09:00:01</code>, watermark w1 = <code>6:00:31</code> is emitted since no tuples earlier than <code>6:00:31</code> can arrive.</p>
+
+<p>Three windows will be evaluated. The first window end ts (06:00:10) is computed by taking the earliest event timestamp (06:00:03)
+and computing the ceiling based on the sliding interval (10s).</p>
+
+<ol>
+<li><code>5:59:50 - 06:00:10</code> with tuples e1, e2, e3</li>
+<li><code>6:00:00 - 06:00:20</code> with tuples e1, e2, e3, e4</li>
+<li><code>6:00:10 - 06:00:30</code> with tuples e4, e5</li>
+</ol>
+
+<p>e6 is not evaluated since watermark timestamp <code>6:00:31</code> is older than the tuple ts <code>6:00:36</code>.</p>
+
+<p>Tuples <code>e7(8:00:25), e8(8:00:26), e9(8:00:27), e10(8:00:39)</code> are received between <code>9:00:01</code> and <code>9:00:02</code></p>
+
+<p>At time t = <code>09:00:02</code> another watermark w2 = <code>08:00:34</code> is emitted since no tuples earlier than <code>8:00:34</code> can arrive now.</p>
+
+<p>Three windows will be evaluated,</p>
+
+<ol>
+<li><code>6:00:20 - 06:00:40</code> with tuples e5, e6 (from earlier batch)</li>
+<li><code>6:00:30 - 06:00:50</code> with tuple e6 (from earlier batch)</li>
+<li><code>8:00:10 - 08:00:30</code> with tuples e7, e8, e9</li>
+</ol>
+
+<p>e10 is not evaluated since the tuple ts <code>8:00:39</code> is beyond the watermark time <code>8:00:34</code>.</p>
+
+<p>The window calculation considers the time gaps and computes the windows based on the tuple timestamp.</p>
+
+<h2 id="guarentees">Guarentees</h2>
+
+<p>The windowing functionality in storm core currently provides at-least once guarentee. The values emitted from the bolts
+<code>execute(TupleWindow inputWindow)</code> method are automatically anchored to all the tuples in the inputWindow. The downstream
+bolts are expected to ack the received tuple (i.e the tuple emitted from the windowed bolt) to complete the tuple tree.
+If not the tuples will be replayed and the windowing computation will be re-evaluated. </p>
+
+<p>The tuples in the window are automatically acked when the expire, i.e. when they fall out of the window after
+<code>windowLength + slidingInterval</code>. Note that the configuration <code>topology.message.timeout.secs</code> should be sufficiently more
+than <code>windowLength + slidingInterval</code> for time based windows; otherwise the tuples will timeout and get replayed and can result
+in duplicate evaluations. For count based windows, the configuration should be adjusted such that <code>windowLength + slidingInterval</code>
+tuples can be received within the timeout period.</p>
+
+<h2 id="example-topology">Example topology</h2>
+
+<p>An example toplogy <code>SlidingWindowTopology</code> shows how to use the apis to compute a sliding window sum and a tumbling window
+average.</p>
+
+
+
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