org.apache.spark.broadcast

Class Broadcast<T>

Object

org.apache.spark.broadcast.Broadcast<T>

All Implemented Interfaces:

java.io.Serializable

public abstract class Broadcast<T>
extends Object
implements java.io.Serializable

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.

Broadcast variables are created from a variable v by calling SparkContext.broadcast(T, scala.reflect.ClassTag<T>). The broadcast variable is a wrapper around v, and its value can be accessed by calling the value method. The interpreter session below shows this:

 scala> val broadcastVar = sc.broadcast(Array(1, 2, 3))
 broadcastVar: org.apache.spark.broadcast.Broadcast[Array[Int} = Broadcast(0)

 scala> broadcastVar.value
 res0: Array[Int] = Array(1, 2, 3)
 

After the broadcast variable is created, it should be used instead of the value v in any functions run on the cluster so that v is not shipped to the nodes more than once. In addition, the object v 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).

param: id A unique identifier for the broadcast variable.

See Also:

Serialized Form

Constructor Summary

Constructors

Constructor and Description
Broadcast(long id, scala.reflect.ClassTag<T> evidence$1)

Method Summary

Methods

Modifier and Type	Method and Description
void	destroy() Destroy all data and metadata related to this broadcast variable.
long	id()
String	toString()
void	unpersist() Asynchronously delete cached copies of this broadcast on the executors.
void	unpersist(boolean blocking) Delete cached copies of this broadcast on the executors.
T	value() Get the broadcasted value.

Methods inherited from class Object

equals, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

Broadcast

public Broadcast(long id,
         scala.reflect.ClassTag<T> evidence$1)

Method Detail

id

public long id()

value

public T value()

Get the broadcasted value.

unpersist

public void unpersist()

Asynchronously 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.

unpersist

public void unpersist(boolean blocking)

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.

Parameters:

blocking - Whether to block until unpersisting has completed

destroy

public void destroy()

Destroy all data and metadata related to this broadcast variable. Use this with caution; once a broadcast variable has been destroyed, it cannot be used again. This method blocks until destroy has completed

toString

public String toString()

Overrides:

toString in class Object