MemoryStore

Memory store (MemoryStore) manages blocks.

MemoryStore requires SparkConf, BlockInfoManager, SerializerManager, MemoryManager and BlockEvictionHandler.

Table 1. MemoryStore Internal Registries
Name Description

entries

Collection of …​FIXME

entries is Java’s LinkedHashMap with the initial capacity of 32, the load factor of 0.75 and access-order ordering mode (i.e. iteration is in the order in which its entries were last accessed, from least-recently accessed to most-recently).

NOTE: entries is Java’s java.util.LinkedHashMap.
Caution
 FIXME Where are these dependencies used?
Caution
 FIXME Where is the MemoryStore created? What params provided?
Note
 MemoryStore is a private[spark] class.
Tip

Enable INFO or DEBUG logging level for org.apache.spark.storage.memory.MemoryStore logger to see what happens inside.

Add the following line to conf/log4j.properties:

log4j.logger.org.apache.spark.storage.memory.MemoryStore=DEBUG

Refer to Logging.

releaseUnrollMemoryForThisTask Method

Caution
 FIXME

getValues Method

getValues(blockId: BlockId): Option[Iterator[_]]

getValues does…​FIXME

getBytes Method

getBytes(blockId: BlockId): Option[ChunkedByteBuffer]

getBytes does…​FIXME

Is Block Available? — contains Method

contains(blockId: BlockId): Boolean

contains returns true when the internal entries registry contains blockId.

putIteratorAsBytes Method

putIteratorAsBytes[T](
  blockId: BlockId,
  values: Iterator[T],
  classTag: ClassTag[T],
  memoryMode: MemoryMode): Either[PartiallySerializedBlock[T], Long]

putIteratorAsBytes tries to put the blockId block in memory store as bytes.

Caution
 FIXME

putIteratorAsValues Method

putIteratorAsValues[T](
  blockId: BlockId,
  values: Iterator[T],
  classTag: ClassTag[T]): Either[PartiallyUnrolledIterator[T], Long]

putIteratorAsValues tries to put the blockId block in memory store as values.

Note
 putIteratorAsValues is a private[storage] method.
Note
 is called when BlockManager stores bytes of a block or iterator of values of a block or when attempting to cache spilled values read from disk.

Evicting Blocks to Free Space

Caution
 FIXME

Removing Block

Caution
 FIXME

Acquiring Storage Memory for Blocks — putBytes Method

putBytes[T](
  blockId: BlockId,
  size: Long,
  memoryMode: MemoryMode,
  _bytes: () => ChunkedByteBuffer): Boolean

putBytes requests storage memory for blockId from MemoryManager and registers the block in entries internal registry.

Internally, putBytes first makes sure that blockId block has not been registered already in entries internal registry.

putBytes then requests size memory for the blockId block in a given memoryMode from the current MemoryManager.

Note

memoryMode can be ON_HEAP or OFF_HEAP and is a property of a StorageLevel.

import org.apache.spark.storage.StorageLevel._
scala> MEMORY_AND_DISK.useOffHeap
res0: Boolean = false

scala> OFF_HEAP.useOffHeap
res1: Boolean = true

If successful, putBytes "materializes" _bytes byte buffer and makes sure that the size is exactly size. It then registers a SerializedMemoryEntry (for the bytes and memoryMode) for blockId in the internal entries registry.

You should see the following INFO message in the logs:

INFO Block [blockId] stored as bytes in memory (estimated size [size], free [bytes])

putBytes returns true only after blockId was successfully registered in the internal entries registry.

Settings

Table 2. Spark Properties
Spark Property Default Value Description

spark.storage.unrollMemoryThreshold

1k

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