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BlockManager

BlockManager manages the storage for blocks (chunks of data) that can be stored in memory and on disk.

BlockManager and Stores

BlockManager runs as part of the driver and executor processes.

BlockManager provides interface for uploading and fetching blocks both locally and remotely using various stores (i.e. memory, disk, and off-heap).

Cached blocks are blocks with non-zero sum of memory and disk sizes.

Tip

Use Web UI (esp. Storage and Executors tabs) to monitor the memory used.

Tip

Use spark-submit's command-line options (i.e. --driver-memory for the driver and --executor-memory for executors) or their equivalents as Spark properties (i.e. spark.executor.memory and spark.driver.memory) to control the memory for storage memory.

When External Shuffle Service is enabled, BlockManager uses ExternalShuffleClient to read shuffle files (of other executors).

Creating Instance

BlockManager takes the following to be created:

When created, BlockManager sets externalShuffleServiceEnabled internal flag based on spark.shuffle.service.enabled configuration property.

BlockManager then creates an instance of DiskBlockManager (requesting deleteFilesOnStop when an external shuffle service is not in use).

BlockManager creates block-manager-future daemon cached thread pool with 128 threads maximum (as futureExecutionContext).

BlockManager calculates the maximum memory to use (as maxMemory) by requesting the maximum on-heap and off-heap storage memory from the assigned MemoryManager.

BlockManager calculates the port used by the external shuffle service (as externalShuffleServicePort).

BlockManager creates a client to read other executors' shuffle files (as shuffleClient). If the external shuffle service is used...FIXME

BlockManager sets the maximum number of failures before this block manager refreshes the block locations from the driver (as maxFailuresBeforeLocationRefresh).

BlockManager registers a BlockManagerSlaveEndpoint with the input RpcEnv, itself, and MapOutputTracker (as slaveEndpoint).

BlockManager is created when SparkEnv is created (for the driver and executors) when a Spark application starts.

BlockManager and SparkEnv

MemoryManager

BlockManager is given a MemoryManager when created.

BlockManager uses the MemoryManager for the following:

DiskBlockManager

BlockManager creates a DiskBlockManager when created.

DiskBlockManager and BlockManager

BlockManager uses the BlockManager for the following:

The DiskBlockManager is available as diskBlockManager reference to other Spark systems.

import org.apache.spark.SparkEnv
SparkEnv.get.blockManager.diskBlockManager

MigratableResolver

migratableResolver: MigratableResolver

BlockManager creates a reference to a MigratableResolver by requesting the ShuffleManager for the ShuffleBlockResolver (that is assumed a MigratableResolver).

Lazy Value

migratableResolver is a Scala lazy value to guarantee that the code to initialize it is executed once only (when accessed for the first time) and the computed value never changes afterwards.

private[storage]

migratableResolver is a private[storage] so it is available to others in the org.apache.spark.storage package.

migratableResolver is used when:

Local Directories for Block Storage

getLocalDiskDirs: Array[String]

getLocalDiskDirs requests the DiskBlockManager for the local directories for block storage.

getLocalDiskDirs is part of the BlockDataManager abstraction.

getLocalDiskDirs is also used by BlockManager when requested for the following:

Initializing BlockManager

initialize(
  appId: String): Unit

initialize requests the BlockTransferService to initialize.

initialize requests the ExternalBlockStoreClient to initialize (if given).

initialize determines the BlockReplicationPolicy based on spark.storage.replication.policy configuration property and prints out the following INFO message to the logs:

Using [priorityClass] for block replication policy

initialize creates a BlockManagerId and requests the BlockManagerMaster to registerBlockManager (with the BlockManagerId, the local directories of the DiskBlockManager, the maxOnHeapMemory, the maxOffHeapMemory and the slaveEndpoint).

initialize sets the internal BlockManagerId to be the response from the BlockManagerMaster (if available) or the BlockManagerId just created.

initialize initializes the External Shuffle Server's Address when enabled and prints out the following INFO message to the logs (with the externalShuffleServicePort):

external shuffle service port = [externalShuffleServicePort]

(only for executors and External Shuffle Service enabled) initialize registers with the External Shuffle Server.

initialize determines the hostLocalDirManager. With spark.shuffle.readHostLocalDisk configuration property enabled and spark.shuffle.useOldFetchProtocol disabled, initialize uses the ExternalBlockStoreClient to create a HostLocalDirManager (with spark.storage.localDiskByExecutors.cacheSize configuration property).

In the end, initialize prints out the following INFO message to the logs (with the blockManagerId):

Initialized BlockManager: [blockManagerId]

initialize is used when:

  • SparkContext is created (on the driver)
  • Executor is created (with isLocal flag disabled)

Registering Executor's BlockManager with External Shuffle Server

registerWithExternalShuffleServer(): Unit

registerWithExternalShuffleServer registers the BlockManager (for an executor) with External Shuffle Service.

registerWithExternalShuffleServer prints out the following INFO message to the logs:

Registering executor with local external shuffle service.

registerWithExternalShuffleServer creates an ExecutorShuffleInfo (with the localDirs and subDirsPerLocalDir of the DiskBlockManager, and the class name of the ShuffleManager).

registerWithExternalShuffleServer uses spark.shuffle.registration.maxAttempts configuration property and 5 sleep time when requesting the ExternalBlockStoreClient to registerWithShuffleServer (using the BlockManagerId and the ExecutorShuffleInfo).

In case of any exception that happen below the maximum number of attempts, registerWithExternalShuffleServer prints out the following ERROR message to the logs and sleeps 5 seconds:

Failed to connect to external shuffle server, will retry [attempts] more times after waiting 5 seconds...

BlockManagerId

BlockManager uses a BlockManagerId for...FIXME

HostLocalDirManager

BlockManager can use a HostLocalDirManager.

Default: (undefined)

BlockReplicationPolicy

BlockManager uses a BlockReplicationPolicy for...FIXME

External Shuffle Service's Port

BlockManager determines the port of an external shuffle service when created.

The port is used to create the shuffleServerId and a HostLocalDirManager.

The port is also used for preferExecutors.

spark.diskStore.subDirectories Configuration Property

BlockManager uses spark.diskStore.subDirectories configuration property to initialize a subDirsPerLocalDir local value.

subDirsPerLocalDir is used when:

Fetching Block or Computing (and Storing) it

getOrElseUpdate[T](
  blockId: BlockId,
  level: StorageLevel,
  classTag: ClassTag[T],
  makeIterator: () => Iterator[T]): Either[BlockResult, Iterator[T]]

Map.getOrElseUpdate

I think it is fair to say that getOrElseUpdate is like getOrElseUpdate of scala.collection.mutable.Map in Scala.

getOrElseUpdate(key: K, op:  V): V

Quoting the official scaladoc:

If given key K is already in this map, getOrElseUpdate returns the associated value V.

Otherwise, getOrElseUpdate computes a value V from given expression op, stores with the key K in the map and returns that value.

Since BlockManager is a key-value store of blocks of data identified by a block ID that seems to fit so well.

getOrElseUpdate first attempts to get the block by the BlockId (from the local block manager first and, if unavailable, requesting remote peers).

getOrElseUpdate gives the BlockResult of the block if found.

If however the block was not found (in any block manager in a Spark cluster), getOrElseUpdate doPutIterator (for the input BlockId, the makeIterator function and the StorageLevel).

getOrElseUpdate branches off per the result:

  • For None, getOrElseUpdate getLocalValues for the BlockId and eventually returns the BlockResult (unless terminated by a SparkException due to some internal error)
  • For Some(iter), getOrElseUpdate returns an iterator of T values

getOrElseUpdate is used when:

Fetching Block

get[T: ClassTag](
  blockId: BlockId): Option[BlockResult]

get attempts to fetch the block (BlockId) from a local block manager first before requesting it from remote block managers. get returns a BlockResult or None (to denote "a block is not available").


Internally, get tries to fetch the block from the local BlockManager. If found, get prints out the following INFO message to the logs and returns a BlockResult.

Found block [blockId] locally

If however the block was not found locally, get tries to fetch the block from remote BlockManagers. If fetched, get prints out the following INFO message to the logs and returns a BlockResult.

Found block [blockId] remotely

getRemoteValues

getRemoteValues[T: ClassTag](
  blockId: BlockId): Option[BlockResult]

getRemoteValues getRemoteBlock with the bufferTransformer function that takes a ManagedBuffer and does the following:

Fetching Block Bytes From Remote Block Managers

getRemoteBytes(
  blockId: BlockId): Option[ChunkedByteBuffer]

getRemoteBytes getRemoteBlock with the bufferTransformer function that takes a ManagedBuffer and creates a ChunkedByteBuffer.

getRemoteBytes is used when:

Fetching Remote Block

getRemoteBlock[T](
  blockId: BlockId,
  bufferTransformer: ManagedBuffer => T): Option[T]

getRemoteBlock is used for getRemoteValues and getRemoteBytes.

getRemoteBlock prints out the following DEBUG message to the logs:

Getting remote block [blockId]

getRemoteBlock requests the BlockManagerMaster for locations and status of the input BlockId (with the host of BlockManagerId).

With some locations, getRemoteBlock determines the size of the block (max of diskSize and memSize). getRemoteBlock tries to read the block from the local directories of another executor on the same host. getRemoteBlock prints out the following INFO message to the logs:

Read [blockId] from the disk of a same host executor is [successful|failed].

When a data block could not be found in any of the local directories, getRemoteBlock fetchRemoteManagedBuffer.

For no locations from the BlockManagerMaster, getRemoteBlock prints out the following DEBUG message to the logs:

readDiskBlockFromSameHostExecutor

readDiskBlockFromSameHostExecutor(
  blockId: BlockId,
  localDirs: Array[String],
  blockSize: Long): Option[ManagedBuffer]

readDiskBlockFromSameHostExecutor...FIXME

fetchRemoteManagedBuffer

fetchRemoteManagedBuffer(
  blockId: BlockId,
  blockSize: Long,
  locationsAndStatus: BlockManagerMessages.BlockLocationsAndStatus): Option[ManagedBuffer]

fetchRemoteManagedBuffer...FIXME

sortLocations

sortLocations(
  locations: Seq[BlockManagerId]): Seq[BlockManagerId]

sortLocations...FIXME

preferExecutors

preferExecutors(
  locations: Seq[BlockManagerId]): Seq[BlockManagerId]

preferExecutors...FIXME

readDiskBlockFromSameHostExecutor

readDiskBlockFromSameHostExecutor(
  blockId: BlockId,
  localDirs: Array[String],
  blockSize: Long): Option[ManagedBuffer]

readDiskBlockFromSameHostExecutor...FIXME

ExecutionContextExecutorService

BlockManager uses a Scala ExecutionContextExecutorService to execute FIXME asynchronously (on a thread pool with block-manager-future prefix and maximum of 128 threads).

BlockEvictionHandler

BlockManager is a BlockEvictionHandler that can drop a block from memory (and store it on a disk when necessary).

ShuffleClient and External Shuffle Service

Danger

FIXME ShuffleClient and ExternalShuffleClient are dead. Long live BlockStoreClient and ExternalBlockStoreClient.

BlockManager manages the lifecycle of a ShuffleClient:

The ShuffleClient can be an ExternalShuffleClient or the given BlockTransferService based on spark.shuffle.service.enabled configuration property. When enabled, BlockManager uses the ExternalShuffleClient.

The ShuffleClient is available to other Spark services (using shuffleClient value) and is used when BlockStoreShuffleReader is requested to read combined key-value records for a reduce task.

When requested for shuffle metrics, BlockManager simply requests them from the ShuffleClient.

BlockManager and RpcEnv

BlockManager is given a RpcEnv when created.

The RpcEnv is used to set up a BlockManagerSlaveEndpoint.

BlockInfoManager

BlockManager creates a BlockInfoManager when created.

BlockManager requests the BlockInfoManager to clear when requested to stop.

BlockManager uses the BlockInfoManager to create a MemoryStore.

BlockManager uses the BlockInfoManager when requested for the following:

BlockManager and BlockManagerMaster

BlockManager is given a BlockManagerMaster when created.

BlockManager as BlockDataManager

BlockManager is a BlockDataManager.

BlockManager and MapOutputTracker

BlockManager is given a MapOutputTracker when created.

Executor ID

BlockManager is given an Executor ID when created.

The Executor ID is one of the following:

BlockManagerEndpoint RPC Endpoint

BlockManager requests the RpcEnv to register a BlockManagerSlaveEndpoint under the name BlockManagerEndpoint[ID].

The RPC endpoint is used when BlockManager is requested to initialize and reregister (to register the BlockManager on an executor with the BlockManagerMaster on the driver).

The endpoint is stopped (by requesting the RpcEnv to stop the reference) when BlockManager is requested to stop.

Accessing BlockManager

BlockManager is available using SparkEnv on the driver and executors.

import org.apache.spark.SparkEnv
val bm = SparkEnv.get.blockManager

scala> :type bm
org.apache.spark.storage.BlockManager

BlockStoreClient

BlockManager uses a BlockStoreClient to read other executors' blocks. This is an ExternalBlockStoreClient (when given and an external shuffle service is used) or a BlockTransferService (to directly connect to other executors).

This BlockStoreClient is used when:

BlockTransferService

BlockManager is given a BlockTransferService when created.

Note

There is only one concrete BlockTransferService that is NettyBlockTransferService and there seem to be no way to reconfigure Apache Spark to use a different implementation (if there were any).

BlockTransferService is used when BlockManager is requested to fetch a block from and replicate a block to remote block managers.

BlockTransferService is used as the BlockStoreClient (unless an ExternalBlockStoreClient is specified).

BlockTransferService is initialized with this BlockManager.

BlockTransferService is closed when BlockManager is requested to stop.

ShuffleManager

BlockManager is given a ShuffleManager when created.

BlockManager uses the ShuffleManager for the following:

MemoryStore

BlockManager creates a MemoryStore when created (with the BlockInfoManager, the SerializerManager, the MemoryManager and itself as a BlockEvictionHandler).

MemoryStore and BlockManager

BlockManager requests the MemoryManager to use the MemoryStore.

BlockManager uses the MemoryStore for the following:

The MemoryStore is requested to clear when BlockManager is requested to stop.

The MemoryStore is available as memoryStore private reference to other Spark services.

import org.apache.spark.SparkEnv
SparkEnv.get.blockManager.memoryStore

The MemoryStore is used (via SparkEnv.get.blockManager.memoryStore reference) when Task is requested to run (that has just finished execution and requests the MemoryStore to release unroll memory).

DiskStore

BlockManager creates a DiskStore (with the DiskBlockManager) when created.

DiskStore and BlockManager

BlockManager uses the DiskStore when requested for the following:

DiskStore is used when:

Performance Metrics

BlockManager uses BlockManagerSource to report metrics under the name BlockManager.

getPeers

getPeers(
  forceFetch: Boolean): Seq[BlockManagerId]

getPeers...FIXME

getPeers is used when BlockManager is requested to replicateBlock and replicate.

Releasing All Locks For Task

releaseAllLocksForTask(
  taskAttemptId: Long): Seq[BlockId]

releaseAllLocksForTask...FIXME

releaseAllLocksForTask is used when TaskRunner is requested to run (at the end of a task).

Stopping BlockManager

stop(): Unit

stop...FIXME

stop is used when SparkEnv is requested to stop.

Getting IDs of Existing Blocks (For a Given Filter)

getMatchingBlockIds(
  filter: BlockId => Boolean): Seq[BlockId]

getMatchingBlockIds...FIXME

getMatchingBlockIds is used when BlockManagerSlaveEndpoint is requested to handle a GetMatchingBlockIds message.

Getting Local Block

getLocalValues(
  blockId: BlockId): Option[BlockResult]

getLocalValues prints out the following DEBUG message to the logs:

Getting local block [blockId]

getLocalValues obtains a read lock for blockId.

When no blockId block was found, you should see the following DEBUG message in the logs and getLocalValues returns "nothing" (i.e. NONE).

Block [blockId] was not found

When the blockId block was found, you should see the following DEBUG message in the logs:

Level for block [blockId] is [level]

If blockId block has memory level and is registered in MemoryStore, getLocalValues returns a BlockResult as Memory read method and with a CompletionIterator for an interator:

  1. Values iterator from MemoryStore for blockId for "deserialized" persistence levels.
  2. Iterator from SerializerManager after the data stream has been deserialized for the blockId block and the bytes for blockId block for "serialized" persistence levels.

getLocalValues is used when:

maybeCacheDiskValuesInMemory

maybeCacheDiskValuesInMemory[T](
  blockInfo: BlockInfo,
  blockId: BlockId,
  level: StorageLevel,
  diskIterator: Iterator[T]): Iterator[T]

maybeCacheDiskValuesInMemory...FIXME

Retrieving Block Data

getBlockData(
  blockId: BlockId): ManagedBuffer

getBlockData is part of the BlockDataManager abstraction.

For a BlockId.md[] of a shuffle (a ShuffleBlockId), getBlockData requests the <> for the shuffle:ShuffleManager.md#shuffleBlockResolver[ShuffleBlockResolver] that is then requested for shuffle:ShuffleBlockResolver.md#getBlockData[getBlockData].

Otherwise, getBlockData <> for the given BlockId.

If found, getBlockData creates a new BlockManagerManagedBuffer (with the <>, the input BlockId, the retrieved BlockData and the dispose flag enabled).

If not found, getBlockData <> that the block could not be found (and that the master should no longer assume the block is available on this executor) and throws a BlockNotFoundException.

NOTE: getBlockData is executed for shuffle blocks or local blocks that the BlockManagerMaster knows this executor really has (unless BlockManagerMaster is outdated).

Retrieving Non-Shuffle Local Block Data

getLocalBytes(
  blockId: BlockId): Option[BlockData]

getLocalBytes...FIXME

getLocalBytes is used when:

  • TorrentBroadcast is requested to readBlocks
  • BlockManager is requested for the block data (of a non-shuffle block)

Storing Block Data Locally

putBlockData(
  blockId: BlockId,
  data: ManagedBuffer,
  level: StorageLevel,
  classTag: ClassTag[_]): Boolean

putBlockData is part of the BlockDataManager abstraction.

putBlockData putBytes with Java NIO's ByteBuffer of the given ManagedBuffer.

Storing Block (ByteBuffer) Locally

putBytes(
  blockId: BlockId,
  bytes: ChunkedByteBuffer,
  level: StorageLevel,
  tellMaster: Boolean = true): Boolean

putBytes creates a ByteBufferBlockStoreUpdater that is then requested to store the bytes.

putBytes is used when:

doPutBytes

doPutBytes[T](
  blockId: BlockId,
  bytes: ChunkedByteBuffer,
  level: StorageLevel,
  classTag: ClassTag[T],
  tellMaster: Boolean = true,
  keepReadLock: Boolean = false): Boolean

doPutBytes calls the internal helper <> with a function that accepts a BlockInfo and does the uploading.

Inside the function, if the StorageLevel.md[storage level]'s replication is greater than 1, it immediately starts <> of the blockId block on a separate thread (from futureExecutionContext thread pool). The replication uses the input bytes and level storage level.

For a memory storage level, the function checks whether the storage level is deserialized or not. For a deserialized storage level, BlockManager's serializer:SerializerManager.md#dataDeserializeStream[SerializerManager deserializes bytes into an iterator of values] that MemoryStore.md#putIteratorAsValues[MemoryStore stores]. If however the storage level is not deserialized, the function requests MemoryStore.md#putBytes[MemoryStore to store the bytes]

If the put did not succeed and the storage level is to use disk, you should see the following WARN message in the logs:

Persisting block [blockId] to disk instead.

And DiskStore.md#putBytes[DiskStore stores the bytes].

NOTE: DiskStore.md[DiskStore] is requested to store the bytes of a block with memory and disk storage level only when MemoryStore.md[MemoryStore] has failed.

If the storage level is to use disk only, DiskStore.md#putBytes[DiskStore stores the bytes].

doPutBytes requests <> and if the block was successfully stored, and the driver should know about it (tellMaster), the function <>. The executor:TaskMetrics.md#incUpdatedBlockStatuses[current TaskContext metrics are updated with the updated block status] (only when executed inside a task where TaskContext is available).

You should see the following DEBUG message in the logs:

Put block [blockId] locally took [time] ms

The function waits till the earlier asynchronous replication finishes for a block with replication level greater than 1.

The final result of doPutBytes is the result of storing the block successful or not (as computed earlier).

NOTE: doPutBytes is used exclusively when BlockManager is requested to <>.

Putting New Block

doPut[T](
  blockId: BlockId,
  level: StorageLevel,
  classTag: ClassTag[_],
  tellMaster: Boolean,
  keepReadLock: Boolean)(putBody: BlockInfo => Option[T]): Option[T]

doPut requires that the given StorageLevel is valid.

doPut creates a new BlockInfo and requests the BlockInfoManager for a write lock for the block.

doPut executes the given putBody function (with the BlockInfo).

If the result of putBody function is None, the block is considered saved successfully.

For successful save, doPut requests the BlockInfoManager to downgradeLock or unlock based on the given keepReadLock flag (true and false, respectively).

For unsuccessful save (when putBody returned some value), doPut removeBlockInternal and prints out the following WARN message to the logs:

Putting block [blockId] failed

In the end, doPut prints out the following DEBUG message to the logs:

Putting block [blockId] [withOrWithout] replication took [usedTime] ms

doPut is used when:

Removing Block

removeBlock(
  blockId: BlockId,
  tellMaster: Boolean = true): Unit

removeBlock prints out the following DEBUG message to the logs:

Removing block [blockId]

removeBlock requests the BlockInfoManager for write lock on the block.

With a write lock on the block, removeBlock removeBlockInternal (with the tellMaster flag turned on when the input tellMaster flag and the tellMaster of the block itself are both turned on).

In the end, removeBlock addUpdatedBlockStatusToTaskMetrics (with an empty BlockStatus).


In case the block is no longer available (None), removeBlock prints out the following WARN message to the logs:

Asked to remove block [blockId], which does not exist

removeBlock is used when:

Removing RDD Blocks

removeRdd(
  rddId: Int): Int

removeRdd removes all the blocks that belong to the rddId RDD.

It prints out the following INFO message to the logs:

Removing RDD [rddId]

It then requests RDD blocks from BlockInfoManager.md[] and <> (without informing the driver).

The number of blocks removed is the final result.

NOTE: It is used by BlockManagerSlaveEndpoint.md#RemoveRdd[BlockManagerSlaveEndpoint while handling RemoveRdd messages].

Removing All Blocks of Broadcast Variable

removeBroadcast(broadcastId: Long, tellMaster: Boolean): Int

removeBroadcast removes all the blocks of the input broadcastId broadcast.

Internally, it starts by printing out the following DEBUG message to the logs:

Removing broadcast [broadcastId]

It then requests all the BlockId.md#BroadcastBlockId[BroadcastBlockId] objects that belong to the broadcastId broadcast from BlockInfoManager.md[] and <>.

The number of blocks removed is the final result.

NOTE: It is used by BlockManagerSlaveEndpoint.md#RemoveBroadcast[BlockManagerSlaveEndpoint while handling RemoveBroadcast messages].

External Shuffle Server's Address

shuffleServerId: BlockManagerId

When requested to initialize, BlockManager records the location (BlockManagerId) of External Shuffle Service if enabled or simply uses the non-external-shuffle-service BlockManagerId.

The BlockManagerId is used to register an executor with a local external shuffle service.

The BlockManagerId is used as the location of a shuffle map output when:

getStatus

getStatus(
  blockId: BlockId): Option[BlockStatus]

getStatus...FIXME

getStatus is used when BlockManagerSlaveEndpoint is requested to handle GetBlockStatus message.

Re-registering BlockManager with Driver

reregister(): Unit

reregister prints out the following INFO message to the logs:

BlockManager [blockManagerId] re-registering with master

reregister requests the BlockManagerMaster to register this BlockManager.

In the end, reregister reportAllBlocks.

reregister is used when:

Reporting All Blocks

reportAllBlocks(): Unit

reportAllBlocks prints out the following INFO message to the logs:

Reporting [n] blocks to the master.

For all the blocks in the BlockInfoManager, reportAllBlocks getCurrentBlockStatus and tryToReportBlockStatus (for blocks tracked by the master).

reportAllBlocks prints out the following ERROR message to the logs and exits when block status reporting fails for any block:

Failed to report [blockId] to master; giving up.

Calculate Current Block Status

getCurrentBlockStatus(
  blockId: BlockId,
  info: BlockInfo): BlockStatus

getCurrentBlockStatus gives the current BlockStatus of the BlockId block (with the block's current StorageLevel.md[StorageLevel], memory and disk sizes). It uses MemoryStore.md[MemoryStore] and DiskStore.md[DiskStore] for size and other information.

NOTE: Most of the information to build BlockStatus is already in BlockInfo except that it may not necessarily reflect the current state per MemoryStore.md[MemoryStore] and DiskStore.md[DiskStore].

Internally, it uses the input BlockInfo.md[] to know about the block's storage level. If the storage level is not set (i.e. null), the returned BlockStatus assumes the StorageLevel.md[default NONE storage level] and the memory and disk sizes being 0.

If however the storage level is set, getCurrentBlockStatus uses MemoryStore.md[MemoryStore] and DiskStore.md[DiskStore] to check whether the block is stored in the storages or not and request for their sizes in the storages respectively (using their getSize or assume 0).

NOTE: It is acceptable that the BlockInfo says to use memory or disk yet the block is not in the storages (yet or anymore). The method will give current status.

getCurrentBlockStatus is used when <>, <> or <> or <>.

Reporting Current Storage Status of Block to Driver

reportBlockStatus(
  blockId: BlockId,
  status: BlockStatus,
  droppedMemorySize: Long = 0L): Unit

reportBlockStatus tryToReportBlockStatus.

If told to re-register, reportBlockStatus prints out the following INFO message to the logs followed by asynchronous re-registration:

Got told to re-register updating block [blockId]

In the end, reportBlockStatus prints out the following DEBUG message to the logs:

Told master about block [blockId]

reportBlockStatus is used when:

Reporting Block Status Update to Driver

tryToReportBlockStatus(
  blockId: BlockId,
  status: BlockStatus,
  droppedMemorySize: Long = 0L): Boolean

tryToReportBlockStatus reports block status update to the BlockManagerMaster and returns its response.

tryToReportBlockStatus is used when:

Execution Context

block-manager-future is the execution context for...FIXME

ByteBuffer

The underlying abstraction for blocks in Spark is a ByteBuffer that limits the size of a block to 2GB (Integer.MAX_VALUE - see Why does FileChannel.map take up to Integer.MAX_VALUE of data? and SPARK-1476 2GB limit in spark for blocks). This has implication not just for managed blocks in use, but also for shuffle blocks (memory mapped blocks are limited to 2GB, even though the API allows for long), ser-deser via byte array-backed output streams.

BlockResult

BlockResult is a metadata of a fetched block:

BlockResult is created and returned when BlockManager is requested for the following:

DataReadMethod

DataReadMethod describes how block data was read.

DataReadMethod Source
Disk DiskStore (while getLocalValues)
Hadoop seems unused
Memory MemoryStore (while getLocalValues)
Network Remote BlockManagers (aka network)

Registering Task

registerTask(
  taskAttemptId: Long): Unit

registerTask requests the BlockInfoManager to register a given task.

registerTask is used when Task is requested to run (at the start of a task).

Creating DiskBlockObjectWriter

getDiskWriter(
  blockId: BlockId,
  file: File,
  serializerInstance: SerializerInstance,
  bufferSize: Int,
  writeMetrics: ShuffleWriteMetrics): DiskBlockObjectWriter

getDiskWriter creates a DiskBlockObjectWriter (with spark.shuffle.sync configuration property for syncWrites argument).

getDiskWriter uses the SerializerManager.

getDiskWriter is used when:

Recording Updated BlockStatus in TaskMetrics (of Current Task)

addUpdatedBlockStatusToTaskMetrics(
  blockId: BlockId,
  status: BlockStatus): Unit

addUpdatedBlockStatusToTaskMetrics takes an active TaskContext (if available) and records updated BlockStatus for Block (in the task's TaskMetrics).

addUpdatedBlockStatusToTaskMetrics is used when BlockManager doPutBytes (for a block that was successfully stored), doPut, doPutIterator, removes blocks from memory (possibly spilling it to disk) and removes block from memory and disk.

Shuffle Metrics Source

shuffleMetricsSource: Source

shuffleMetricsSource creates a ShuffleMetricsSource with the shuffleMetrics (of the BlockStoreClient) and the source name as follows:

shuffleMetricsSource is available using SparkEnv:

env.blockManager.shuffleMetricsSource

shuffleMetricsSource is used when:

  • Executor is created (for non-local / cluster modes)

Replicating Block To Peers

replicate(
  blockId: BlockId,
  data: BlockData,
  level: StorageLevel,
  classTag: ClassTag[_],
  existingReplicas: Set[BlockManagerId] = Set.empty): Unit

replicate...FIXME

replicate is used when BlockManager is requested to doPutBytes, doPutIterator and replicateBlock.

replicateBlock

replicateBlock(
  blockId: BlockId,
  existingReplicas: Set[BlockManagerId],
  maxReplicas: Int): Unit

replicateBlock...FIXME

replicateBlock is used when BlockManagerSlaveEndpoint is requested to handle a ReplicateBlock message.

putIterator

putIterator[T: ClassTag](
  blockId: BlockId,
  values: Iterator[T],
  level: StorageLevel,
  tellMaster: Boolean = true): Boolean

putIterator...FIXME

putIterator is used when:

putSingle

putSingle[T: ClassTag](
  blockId: BlockId,
  value: T,
  level: StorageLevel,
  tellMaster: Boolean = true): Boolean

putSingle...FIXME

putSingle is used when TorrentBroadcast is requested to write the blocks and readBroadcastBlock.

doPutIterator

doPutIterator[T](
  blockId: BlockId,
  iterator: () => Iterator[T],
  level: StorageLevel,
  classTag: ClassTag[T],
  tellMaster: Boolean = true,
  keepReadLock: Boolean = false): Option[PartiallyUnrolledIterator[T]]

doPutIterator doPut with the putBody function.

doPutIterator is used when:

putBody

putBody: BlockInfo => Option[T]

For the given StorageLevel that indicates to use memory for storage, putBody requests the MemoryStore to putIteratorAsValues or putIteratorAsBytes based on the StorageLevel (that indicates to use deserialized format or not, respectively).

In case storing the block in memory was not possible (due to lack of available memory), putBody prints out the following WARN message to the logs and falls back on the DiskStore to store the block.

Persisting block [blockId] to disk instead.

For the given StorageLevel that indicates to use disk storage only (useMemory flag is disabled), putBody requests the DiskStore to store the block.

putBody gets the current block status and checks whether the StorageLevel is valid (that indicates that the block was stored successfully).

If the block was stored successfully, putBody reports the block status (only if indicated by the the given tellMaster flag and the tellMaster flag of the associated BlockInfo) and addUpdatedBlockStatusToTaskMetrics.

putBody prints out the following DEBUG message to the logs:

Put block [blockId] locally took [duration] ms

For the given StorageLevel with replication enabled (above 1), putBody doGetLocalBytes and replicates the block (to other BlockManagers). putBody prints out the following DEBUG message to the logs:

Put block [blockId] remotely took [duration] ms

doGetLocalBytes

doGetLocalBytes(
  blockId: BlockId,
  info: BlockInfo): BlockData

doGetLocalBytes...FIXME

doGetLocalBytes is used when:

Dropping Block from Memory

dropFromMemory(
  blockId: BlockId,
  data: () => Either[Array[T], ChunkedByteBuffer]): StorageLevel

dropFromMemory prints out the following INFO message to the logs:

Dropping block [blockId] from memory

dropFromMemory requests the BlockInfoManager to assert that the block is locked for writing (that gives a BlockInfo or throws a SparkException).


dropFromMemory drops to disk if the current storage level requires so (based on the given BlockInfo) and the block is not in the DiskStore already. dropFromMemory prints out the following INFO message to the logs:

Writing block [blockId] to disk

dropFromMemory uses the given data to determine whether the DiskStore is requested to put or putBytes (Array[T] or ChunkedByteBuffer, respectively).


dropFromMemory requests the MemoryStore to remove the block. dropFromMemory prints out the following WARN message to the logs if the block was not found in the MemoryStore:

Block [blockId] could not be dropped from memory as it does not exist

dropFromMemory gets the current block status and reportBlockStatus when requested (when the tellMaster flag of the BlockInfo is turned on).

dropFromMemory addUpdatedBlockStatusToTaskMetrics when the block has been updated (dropped to disk or removed from the MemoryStore).

In the end, dropFromMemory returns the current StorageLevel of the block (off the BlockStatus).


dropFromMemory is part of the BlockEvictionHandler abstraction.

releaseLock Method

releaseLock(
  blockId: BlockId,
  taskAttemptId: Option[Long] = None): Unit

releaseLock requests the BlockInfoManager to unlock the given block.

releaseLock is part of the BlockDataManager abstraction.

putBlockDataAsStream

putBlockDataAsStream(
  blockId: BlockId,
  level: StorageLevel,
  classTag: ClassTag[_]): StreamCallbackWithID

putBlockDataAsStream is part of the BlockDataManager abstraction.

putBlockDataAsStream...FIXME

Maximum Memory

Total maximum value that BlockManager can ever possibly use (that depends on MemoryManager and may vary over time).

Total available on-heap and off-heap memory for storage (in bytes)

Maximum Off-Heap Memory

Maximum On-Heap Memory

decommissionSelf

decommissionSelf(): Unit

decommissionSelf...FIXME

decommissionSelf is used when:

decommissionBlockManager

decommissionBlockManager(): Unit

decommissionBlockManager sends a DecommissionBlockManager message to the BlockManagerStorageEndpoint.

decommissionBlockManager is used when:

BlockManagerStorageEndpoint

storageEndpoint: RpcEndpointRef

BlockManager sets up a RpcEndpointRef (within the RpcEnv) under the name BlockManagerEndpoint[ID] with a BlockManagerStorageEndpoint message handler.

BlockManagerDecommissioner

decommissioner: Option[BlockManagerDecommissioner]

BlockManager defines decommissioner internal registry for a BlockManagerDecommissioner.

decommissioner is undefined (None) by default.

BlockManager creates and starts a BlockManagerDecommissioner when requested to decommissionSelf.

decommissioner is used for isDecommissioning and lastMigrationInfo.

BlockManager requests the BlockManagerDecommissioner to stop when stopped.

Removing Block from Memory and Disk

removeBlockInternal(
  blockId: BlockId,
  tellMaster: Boolean): Unit

For tellMaster turned on, removeBlockInternal requests the BlockInfoManager to assert that the block is locked for writing and remembers the current block status. Otherwise, removeBlockInternal leaves the block status undetermined.

removeBlockInternal requests the MemoryStore to remove the block.

removeBlockInternal requests the DiskStore to remove the block.

removeBlockInternal requests the BlockInfoManager to remove the block metadata.

In the end, removeBlockInternal reports the block status (to the master) with the storage level changed to NONE.


removeBlockInternal prints out the following WARN message when the block was not stored in the MemoryStore and the DiskStore:

Block [blockId] could not be removed as it was not found on disk or in memory

removeBlockInternal is used when:

maybeCacheDiskBytesInMemory

maybeCacheDiskBytesInMemory(
  blockInfo: BlockInfo,
  blockId: BlockId,
  level: StorageLevel,
  diskData: BlockData): Option[ChunkedByteBuffer]

maybeCacheDiskBytesInMemory...FIXME

maybeCacheDiskBytesInMemory is used when:

Logging

Enable ALL logging level for org.apache.spark.storage.BlockManager logger to see what happens inside.

Add the following line to conf/log4j.properties:

log4j.logger.org.apache.spark.storage.BlockManager=ALL

Refer to Logging.

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