Skip to content

NettyBlockTransferService

= NettyBlockTransferService

NettyBlockTransferService is a storage:BlockTransferService.md[] that uses Netty for <> or <> blocks of data.

.NettyBlockTransferService, SparkEnv and BlockManager image::NettyBlockTransferService.png[align="center"]

== [[creating-instance]] Creating Instance

NettyBlockTransferService takes the following to be created:

  • [[conf]] ROOT:SparkConf.md[SparkConf]
  • [[securityManager]] SecurityManager
  • [[bindAddress]] Bind address
  • [[hostName]] Host name
  • [[_port]] Port number
  • [[numCores]] Number of CPU cores

NettyBlockTransferService is created when SparkEnv is core:SparkEnv.md#create-NettyBlockTransferService[created] for the driver and executors (and core:SparkEnv.md#create-BlockManager[creates the BlockManager]).

== [[transportConf]][[transportContext]] TransportConf, TransportContext

NettyBlockTransferService creates a network:TransportConf.md[] for shuffle module (using network:SparkTransportConf.md#fromSparkConf[SparkTransportConf] utility) when <>.

NettyBlockTransferService uses the TransportConf for the following:

  • Create a network:TransportContext.md[] when requested to <>

  • Create a storage:OneForOneBlockFetcher.md[] and a core:RetryingBlockFetcher.md[RetryingBlockFetcher] when requested to <>

NettyBlockTransferService uses the TransportContext to create the <> and the <>.

== [[clientFactory]] TransportClientFactory

NettyBlockTransferService creates a network:TransportClientFactory.md[] when requested to <>.

NettyBlockTransferService uses the TransportClientFactory for the following:

  • <>

  • <>

  • <>

NettyBlockTransferService requests the TransportClientFactory to network:TransportClientFactory.md#close[close] when requested to <>.

== [[server]] TransportServer

NettyBlockTransferService <> when requested to <>.

NettyBlockTransferService uses the TransportServer for the following:

  • <>

  • <>

NettyBlockTransferService requests the TransportServer to network:TransportServer.md#close[close] when requested to <>.

== [[port]] Port

NettyBlockTransferService simply requests the <> for the network:TransportServer.md#getPort[port].

== [[shuffleMetrics]] Shuffle Metrics

[source,scala]

shuffleMetrics(): MetricSet

shuffleMetrics...FIXME

shuffleMetrics is part of the storage:ShuffleClient.md#shuffleMetrics[ShuffleClient] abstraction.

== [[fetchBlocks]] Fetching Blocks

[source, scala]

fetchBlocks( host: String, port: Int, execId: String, blockIds: Array[String], listener: BlockFetchingListener): Unit


When executed, fetchBlocks prints out the following TRACE message in the logs:

TRACE Fetch blocks from [host]:[port] (executor id [execId])

fetchBlocks then creates a RetryingBlockFetcher.BlockFetchStarter where createAndStart method...FIXME

Depending on the maximum number of acceptable IO exceptions (such as connection timeouts) per request, if the number is greater than 0, fetchBlocks creates a core:RetryingBlockFetcher.md#creating-instance[RetryingBlockFetcher] and core:RetryingBlockFetcher.md#start[starts] it immediately.

NOTE: RetryingBlockFetcher is created with the RetryingBlockFetcher.BlockFetchStarter created earlier, the input blockIds and listener.

If however the number of retries is not greater than 0 (it could be 0 or less), the RetryingBlockFetcher.BlockFetchStarter created earlier is started (with the input blockIds and listener).

In case of any Exception, you should see the following ERROR message in the logs and the input BlockFetchingListener gets notified (using onBlockFetchFailure for every block id).

ERROR Exception while beginning fetchBlocks

fetchBlocks is part of storage:BlockTransferService.md#fetchBlocks[BlockTransferService] abstraction.

== [[appId]] Application Id

== [[close]] Closing NettyBlockTransferService

[source, scala]

close(): Unit

close...FIXME

close is part of the storage:BlockTransferService.md#close[BlockTransferService] abstraction.

== [[init]] Initializing NettyBlockTransferService

[source, scala]

init( blockDataManager: BlockDataManager): Unit


init creates a storage:NettyBlockRpcServer.md[] (for the ROOT:SparkConf.md#getAppId[application id], a JavaSerializer and the given storage:BlockDataManager.md[BlockDataManager]) that is used to create a <>.

init creates the internal clientFactory and a server.

CAUTION: FIXME What's the "a server"?

In the end, you should see the INFO message in the logs:

Server created on [hostName]:[port]

NOTE: hostname is given when core:SparkEnv.md#NettyBlockTransferService[NettyBlockTransferService is created] and is controlled by spark-driver.md#spark_driver_host[spark.driver.host Spark property] for the driver and differs per deployment environment for executors (as controlled by executor:CoarseGrainedExecutorBackend.md#main[--hostname for CoarseGrainedExecutorBackend]).

init is part of the storage:BlockTransferService.md#init[BlockTransferService] abstraction.

== [[uploadBlock]] Uploading Block

[source, scala]

uploadBlock( hostname: String, port: Int, execId: String, blockId: BlockId, blockData: ManagedBuffer, level: StorageLevel, classTag: ClassTag[_]): Future[Unit]


Internally, uploadBlock creates a TransportClient client to send a <UploadBlock message>> (to the input hostname and port).

NOTE: UploadBlock message is processed by storage:NettyBlockRpcServer.md[NettyBlockRpcServer].

The UploadBlock message holds the <>, the input execId and blockId. It also holds the serialized bytes for block metadata with level and classTag serialized (using the internal JavaSerializer) as well as the serialized bytes for the input blockData itself (this time however the serialization uses storage:BlockDataManager.md#ManagedBuffer[ManagedBuffer.nioByteBuffer method]).

The entire UploadBlock message is further serialized before sending (using TransportClient.sendRpc).

CAUTION: FIXME Describe TransportClient and clientFactory.createClient.

When blockId block was successfully uploaded, you should see the following TRACE message in the logs:

TRACE NettyBlockTransferService: Successfully uploaded block [blockId]

When an upload failed, you should see the following ERROR message in the logs:

ERROR Error while uploading block [blockId]

uploadBlock is part of the storage:BlockTransferService.md#uploadBlock[BlockTransferService] abstraction.

== [[UploadBlock]] UploadBlock Message

UploadBlock is a BlockTransferMessage that describes a block being uploaded, i.e. send over the wire from a <> to a storage:NettyBlockRpcServer.md#UploadBlock[NettyBlockRpcServer].

.UploadBlock Attributes [cols="1,2",options="header",width="100%"] |=== | Attribute | Description | appId | The application id (the block belongs to) | execId | The executor id | blockId | The block id | metadata | | blockData | The block data as an array of bytes |===

As an Encodable, UploadBlock can calculate the encoded size and do encoding and decoding itself to or from a ByteBuf, respectively.

== [[createServer]] createServer Internal Method

[source, scala]

createServer( bootstraps: List[TransportServerBootstrap]): TransportServer


createServer...FIXME

createServer is used when NettyBlockTransferService is requested to <>.

== [[logging]] Logging

Enable ALL logging level for org.apache.spark.network.netty.NettyBlockTransferService logger to see what happens inside.

Add the following line to conf/log4j.properties:

[source,plaintext]

log4j.logger.org.apache.spark.network.netty.NettyBlockTransferService=ALL

Refer to ROOT:spark-logging.md[Logging].


Last update: 2020-10-06