Package org.apache.spark.broadcast

Class Broadcast<T>

Object
org.apache.spark.broadcast.Broadcast<T>
Type Parameters:
T - Type of the data contained in the broadcast variable.
All Implemented Interfaces:
Serializable, org.apache.spark.internal.Logging
public abstract class Broadcast<T> extends Object implements Serializable, org.apache.spark.internal.Logging
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:

  • Nested Class Summary

    Nested classes/interfaces inherited from interface org.apache.spark.internal.Logging

    org.apache.spark.internal.Logging.LogStringContext, org.apache.spark.internal.Logging.SparkShellLoggingFilter

  • Constructor Summary

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

  • Method Summary

    Modifier and Type
    Method
    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 java.lang.Object

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

    Methods inherited from interface org.apache.spark.internal.Logging

    initializeForcefully, initializeLogIfNecessary, initializeLogIfNecessary, initializeLogIfNecessary$default$2, isTraceEnabled, log, logDebug, logDebug, logDebug, logDebug, logError, logError, logError, logError, logInfo, logInfo, logInfo, logInfo, logName, LogStringContext, logTrace, logTrace, logTrace, logTrace, logWarning, logWarning, logWarning, logWarning, org$apache$spark$internal$Logging$$log_, org$apache$spark$internal$Logging$$log__$eq, withLogContext

  • Constructor Details

    • Broadcast

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

  • Method Details

    • 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.

    • id

      public long id()

    • toString

      public String toString()
      Overrides:
      toString in class Object

    • 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

    • value

      public T value()
      Get the broadcasted value.