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<p class="subTitle">org.apache.spark.broadcast</p>
<h2 title="Class Broadcast" class="title">Class Broadcast<T></h2>
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<li>Object</li>
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<pre>public abstract class <strong>Broadcast<T></strong>
extends Object
implements java.io.Serializable</pre>
<div class="block">A broadcast variable. Broadcast variables allow the programmer to keep a read-only variable
cached on each machine rather than shipping a copy of it with tasks. They can be used, for
example, to give every node a copy of a large input dataset in an efficient manner. Spark also
attempts to distribute broadcast variables using efficient broadcast algorithms to reduce
communication cost.
<p>
Broadcast variables are created from a variable <code>v</code> by calling
<a href="../../../../org/apache/spark/SparkContext.html#broadcast(T, scala.reflect.ClassTag)"><code>SparkContext.broadcast(T, scala.reflect.ClassTag<T>)</code></a>.
The broadcast variable is a wrapper around <code>v</code>, and its value can be accessed by calling the
<code>value</code> method. The interpreter session below shows this:
<p>
<pre><code>
scala> val broadcastVar = sc.broadcast(Array(1, 2, 3))
broadcastVar: spark.Broadcast[Array[Int} = spark.Broadcast(b5c40191-a864-4c7d-b9bf-d87e1a4e787c)
scala> broadcastVar.value
res0: Array[Int] = Array(1, 2, 3)
</code></pre>
<p>
After the broadcast variable is created, it should be used instead of the value <code>v</code> in any
functions run on the cluster so that <code>v</code> is not shipped to the nodes more than once.
In addition, the object <code>v</code> should not be modified after it is broadcast in order to ensure
that all nodes get the same value of the broadcast variable (e.g. if the variable is shipped
to a new node later).
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<dl><dt><span class="strong">See Also:</span></dt><dd><a href="../../../../serialized-form.html#org.apache.spark.broadcast.Broadcast">Serialized Form</a></dd></dl>
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<td class="colOne"><code><strong><a href="../../../../org/apache/spark/broadcast/Broadcast.html#Broadcast(long, scala.reflect.ClassTag)">Broadcast</a></strong>(long id,
scala.reflect.ClassTag<<a href="../../../../org/apache/spark/broadcast/Broadcast.html" title="type parameter in Broadcast">T</a>> evidence$1)</code> </td>
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<td class="colFirst"><code>long</code></td>
<td class="colLast"><code><strong><a href="../../../../org/apache/spark/broadcast/Broadcast.html#id()">id</a></strong>()</code> </td>
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<td class="colFirst"><code>String</code></td>
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<td class="colFirst"><code>void</code></td>
<td class="colLast"><code><strong><a href="../../../../org/apache/spark/broadcast/Broadcast.html#unpersist()">unpersist</a></strong>()</code>
<div class="block">Asynchronously delete cached copies of this broadcast on the executors.</div>
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<td class="colFirst"><code>void</code></td>
<td class="colLast"><code><strong><a href="../../../../org/apache/spark/broadcast/Broadcast.html#unpersist(boolean)">unpersist</a></strong>(boolean blocking)</code>
<div class="block">Delete cached copies of this broadcast on the executors.</div>
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<td class="colFirst"><code><a href="../../../../org/apache/spark/broadcast/Broadcast.html" title="type parameter in Broadcast">T</a></code></td>
<td class="colLast"><code><strong><a href="../../../../org/apache/spark/broadcast/Broadcast.html#value()">value</a></strong>()</code>
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<pre>public Broadcast(long id,
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<div class="block">Asynchronously delete cached copies of this broadcast on the executors.
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<pre>public void unpersist(boolean blocking)</pre>
<div class="block">Delete cached copies of this broadcast on the executors. If the broadcast is used after
this is called, it will need to be re-sent to each executor.</div>
<dl><dt><span class="strong">Parameters:</span></dt><dd><code>blocking</code> - Whether to block until unpersisting has completed</dd></dl>
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