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| <pre><a href="../../../../../org/apache/beam/sdk/annotations/Experimental.html" title="annotation in org.apache.beam.sdk.annotations">@Experimental</a> |
| public class <span class="typeNameLabel">Wait</span> |
| extends java.lang.Object</pre> |
| <div class="block">Delays processing of each window in a <a href="../../../../../org/apache/beam/sdk/values/PCollection.html" title="class in org.apache.beam.sdk.values"><code>PCollection</code></a> until signaled. |
| |
| <p>Given a main <a href="../../../../../org/apache/beam/sdk/values/PCollection.html" title="class in org.apache.beam.sdk.values"><code>PCollection</code></a> and a signal <a href="../../../../../org/apache/beam/sdk/values/PCollection.html" title="class in org.apache.beam.sdk.values"><code>PCollection</code></a>, produces output identical |
| to its main input, but all elements for a window are produced only once that window is closed in |
| the signal <a href="../../../../../org/apache/beam/sdk/values/PCollection.html" title="class in org.apache.beam.sdk.values"><code>PCollection</code></a>. |
| |
| <p>To express the pattern "apply T to X after Y is ready", use <code>X.apply(Wait.on(Y)).apply(T)</code>. |
| |
| <p>In particular: returns a <a href="../../../../../org/apache/beam/sdk/values/PCollection.html" title="class in org.apache.beam.sdk.values"><code>PCollection</code></a> with contents identical to the input, but delays |
| producing elements of the output in window W until the signal's window W closes (i.e. signal's |
| watermark passes W.end + signal.allowedLateness). |
| |
| <p>In other words, an element of the output at timestamp "t" will be produced only after no more |
| elements of the signal can appear with a timestamp below "t". |
| |
| <p>Example usage: write a <a href="../../../../../org/apache/beam/sdk/values/PCollection.html" title="class in org.apache.beam.sdk.values"><code>PCollection</code></a> to one database and then to another database, |
| making sure that writing a window of data to the second database starts only after the respective |
| window has been fully written to the first database. |
| |
| <pre><code> |
| PCollection<Void> firstWriteResults = data.apply(ParDo.of(...write to first database...)); |
| data.apply(Wait.on(firstWriteResults)) |
| // Windows of this intermediate PCollection will be processed no earlier than when |
| // the respective window of firstWriteResults closes. |
| .apply(ParDo.of(...write to second database...)); |
| </code></pre> |
| |
| <p>Notes: |
| |
| <ul> |
| <li>If signal is globally windowed, main input must also be. This typically would be useful |
| only in a batch pipeline, because the global window of an infinite PCollection never |
| closes, so the wait signal will never be ready. |
| <li>Beware that if the signal has large allowed lateness, the wait signal will fire only after |
| that lateness elapses, i.e. after the watermark of the signal passes end of the window plus |
| allowed lateness. In other words: do not use this with signals that specify a large allowed |
| lateness. |
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| <td class="colFirst"><code>static class </code></td> |
| <td class="colLast"><code><span class="memberNameLink"><a href="../../../../../org/apache/beam/sdk/transforms/Wait.OnSignal.html" title="class in org.apache.beam.sdk.transforms">Wait.OnSignal</a><<a href="../../../../../org/apache/beam/sdk/transforms/Wait.OnSignal.html" title="type parameter in Wait.OnSignal">T</a>></span></code> |
| <div class="block">Implementation of <a href="../../../../../org/apache/beam/sdk/transforms/Wait.html#on-org.apache.beam.sdk.values.PCollection...-"><code>on(org.apache.beam.sdk.values.PCollection<?>...)</code></a>.</div> |
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| <td class="colOne"><code><span class="memberNameLink"><a href="../../../../../org/apache/beam/sdk/transforms/Wait.html#Wait--">Wait</a></span>()</code> </td> |
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| <td class="colFirst"><code>static <T> <a href="../../../../../org/apache/beam/sdk/transforms/Wait.OnSignal.html" title="class in org.apache.beam.sdk.transforms">Wait.OnSignal</a><T></code></td> |
| <td class="colLast"><code><span class="memberNameLink"><a href="../../../../../org/apache/beam/sdk/transforms/Wait.html#on-java.util.List-">on</a></span>(java.util.List<<a href="../../../../../org/apache/beam/sdk/values/PCollection.html" title="class in org.apache.beam.sdk.values">PCollection</a><?>> signals)</code> |
| <div class="block">Waits on the given signal collections.</div> |
| </td> |
| </tr> |
| <tr id="i1" class="rowColor"> |
| <td class="colFirst"><code>static <T> <a href="../../../../../org/apache/beam/sdk/transforms/Wait.OnSignal.html" title="class in org.apache.beam.sdk.transforms">Wait.OnSignal</a><T></code></td> |
| <td class="colLast"><code><span class="memberNameLink"><a href="../../../../../org/apache/beam/sdk/transforms/Wait.html#on-org.apache.beam.sdk.values.PCollection...-">on</a></span>(<a href="../../../../../org/apache/beam/sdk/values/PCollection.html" title="class in org.apache.beam.sdk.values">PCollection</a><?>... signals)</code> |
| <div class="block">Waits on the given signal collections.</div> |
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| <code>clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait</code></li> |
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| <h4>Wait</h4> |
| <pre>public Wait()</pre> |
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| <h4>on</h4> |
| <pre>public static <T> <a href="../../../../../org/apache/beam/sdk/transforms/Wait.OnSignal.html" title="class in org.apache.beam.sdk.transforms">Wait.OnSignal</a><T> on(<a href="../../../../../org/apache/beam/sdk/values/PCollection.html" title="class in org.apache.beam.sdk.values">PCollection</a><?>... signals)</pre> |
| <div class="block">Waits on the given signal collections.</div> |
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| <h4>on</h4> |
| <pre>public static <T> <a href="../../../../../org/apache/beam/sdk/transforms/Wait.OnSignal.html" title="class in org.apache.beam.sdk.transforms">Wait.OnSignal</a><T> on(java.util.List<<a href="../../../../../org/apache/beam/sdk/values/PCollection.html" title="class in org.apache.beam.sdk.values">PCollection</a><?>> signals)</pre> |
| <div class="block">Waits on the given signal collections.</div> |
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