【Spark八十三】BlockManager在Spark中的使用场景

1. Broadcast变量的存储,在HttpBroadcast类中可以知道

2. RDD通过CacheManager存储RDD中的数据,CacheManager也是通过BlockManager进行存储的

3. ShuffleMapTask得到的结果数据,是通过FileShuffleBlockManager进行管理的,而FileShuffleBlockManager最终也是使用BlockManager来对数据块进行管理

4. ResultTask的结果如果非常大,那么使用IndirectTaskResult作为返回结果给Driver,Driver通过IndirectTaskResult反查BlockManager获取数据,通过Netty的数据传输

代码在TaskRunner的run方法中。

 

       // directSend = sending directly back to the driver
        val serializedResult = {
          if (maxResultSize > 0 && resultSize > maxResultSize) {
            logWarning(s"Finished $taskName (TID $taskId). Result is larger than maxResultSize " +
              s"(${Utils.bytesToString(resultSize)} > ${Utils.bytesToString(maxResultSize)}), " +
              s"dropping it.")
            ser.serialize(new IndirectTaskResult[Any](TaskResultBlockId(taskId), resultSize))
          } else if (resultSize >= akkaFrameSize - AkkaUtils.reservedSizeBytes) { //如果结果大于Akka传输的数据量(默认10M)
            val blockId = TaskResultBlockId(taskId)
            env.blockManager.putBytes( //设置到BlockManager中,MEMORY_AND_DISK_SER表示
              blockId, serializedDirectResult, StorageLevel.MEMORY_AND_DISK_SER)
            logInfo(
              s"Finished $taskName (TID $taskId). $resultSize bytes result sent via BlockManager)")
            ser.serialize(new IndirectTaskResult[Any](blockId, resultSize))
          } else {
            logInfo(s"Finished $taskName (TID $taskId). $resultSize bytes result sent to driver")
            serializedDirectResult
          }
        }

 

 5. Spark Streaming将接收到的数据首先写入到BlockManager中

 

关于StorageLevel的设置:

 

class StorageLevel private(
    private var _useDisk: Boolean,
    private var _useMemory: Boolean,
    private var _useOffHeap: Boolean,
    private var _deserialized: Boolean,
    private var _replication: Int = 1)

五个参数:

使用磁盘存储

使用内存存储

使用Tachyon存储

deserialzed表示存储的数据是否是原始数据(没有进行序列化)?

副本数

 

  val NONE = new StorageLevel(false, false, false, false)
  val DISK_ONLY = new StorageLevel(true, false, false, false)
  val DISK_ONLY_2 = new StorageLevel(true, false, false, false, 2)
  val MEMORY_ONLY = new StorageLevel(false, true, false, true)
  val MEMORY_ONLY_2 = new StorageLevel(false, true, false, true, 2)
  val MEMORY_ONLY_SER = new StorageLevel(false, true, false, false)
  val MEMORY_ONLY_SER_2 = new StorageLevel(false, true, false, false, 2)
  val MEMORY_AND_DISK = new StorageLevel(true, true, false, true)
  val MEMORY_AND_DISK_2 = new StorageLevel(true, true, false, true, 2)
  val MEMORY_AND_DISK_SER = new StorageLevel(true, true, false, false)
  val MEMORY_AND_DISK_SER_2 = new StorageLevel(true, true, false, false, 2)
  val OFF_HEAP = new StorageLevel(false, false, true, false)

 

 

 

 

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