abstract class Broadcast[T] extends Serializable with 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
org.apache.spark.SparkContext#broadcast.
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).
- T
Type of the data contained in the broadcast variable.
- Source
- Broadcast.scala
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- Broadcast
- Logging
- Serializable
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Instance Constructors
-
new
Broadcast(id: Long)(implicit arg0: ClassTag[T])
- id
A unique identifier for the broadcast variable.
Concrete Value Members
-
def
destroy(): Unit
Destroy all data and metadata related to this broadcast variable.
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.
- val id: Long
-
def
toString(): String
- Definition Classes
- Broadcast → AnyRef → Any
-
def
unpersist(blocking: Boolean): Unit
Delete cached copies of this broadcast on the executors.
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.
- blocking
Whether to block until unpersisting has completed
-
def
unpersist(): Unit
Asynchronously delete cached copies of this broadcast on the executors.
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.
-
def
value: T
Get the broadcasted value.