= [[UnifiedMemoryManager]] UnifiedMemoryManager
UnifiedMemoryManager is the default MemoryManager.md[MemoryManager] (based on configuration-properties.md#spark.memory.useLegacyMode[spark.memory.useLegacyMode] configuration property).
== [[creating-instance]] Creating Instance
UnifiedMemoryManager takes the following to be created:
- [[conf]] SparkConf.md[SparkConf]
- [[maxHeapMemory]] Maximum heap memory
- [[onHeapStorageRegionSize]] Size of the on-heap storage region
- [[numCores]] Number of CPU cores
UnifiedMemoryManager requires that:
-
Sum of the pool size of the MemoryManager.md#onHeapExecutionMemoryPool[on-heap ExecutionMemoryPool] and MemoryManager.md#onHeapStorageMemoryPool[on-heap StorageMemoryPool] is exactly the <
-
Sum of the pool size of the MemoryManager.md#offHeapExecutionMemoryPool[off-heap ExecutionMemoryPool] and MemoryManager.md#offHeapStorageMemoryPool[off-heap StorageMemoryPool] is exactly the maximum off-heap memory (based on configuration-properties.md#spark.memory.offHeap.size[spark.memory.offHeap.size] configuration property)
== [[apply]] Creating UnifiedMemoryManager
[source, scala]¶
apply( conf: SparkConf, numCores: Int): UnifiedMemoryManager
apply computes the <
apply computes the size of the on-heap storage region which is a fraction of the maximum heap memory based on configuration-properties.md#spark.memory.storageFraction[spark.memory.storageFraction] configuration property (default: 0.5).
In the end, apply creates a <
apply is used when SparkEnv utility is used to core:SparkEnv.md#create[create a SparkEnv] (for the driver and executors).
== [[getMaxMemory]] Calculating Maximum Heap Memory
[source, scala]¶
getMaxMemory( conf: SparkConf): Long
getMaxMemory calculates the maximum memory to use for execution and storage.
[source, scala]¶
// local mode with --conf spark.driver.memory=2g scala> sc.getConf.getSizeAsBytes("spark.driver.memory") res0: Long = 2147483648
scala> val systemMemory = Runtime.getRuntime.maxMemory
// fixed amount of memory for non-storage, non-execution purposes val reservedMemory = 300 * 1024 * 1024
// minimum system memory required val minSystemMemory = (reservedMemory * 1.5).ceil.toLong
val usableMemory = systemMemory - reservedMemory
val memoryFraction = sc.getConf.getDouble("spark.memory.fraction", 0.6) scala> val maxMemory = (usableMemory * memoryFraction).toLong maxMemory: Long = 956615884
import org.apache.spark.network.util.JavaUtils scala> JavaUtils.byteStringAsMb(maxMemory + "b") res1: Long = 912
getMaxMemory reads <
getMaxMemory makes sure that the following requirements are met:
- System memory is not smaller than about 1,5 of the reserved system memory.
- executor:Executor.md#spark.executor.memory[spark.executor.memory] is not smaller than about 1,5 of the reserved system memory.
Ultimately, getMaxMemory returns <
CAUTION: FIXME omnigraffle it.
== [[acquireExecutionMemory]] acquireExecutionMemory Method
[source, scala]¶
acquireExecutionMemory( numBytes: Long, taskAttemptId: Long, memoryMode: MemoryMode): Long
NOTE: acquireExecutionMemory is part of the memory:MemoryManager.md#acquireExecutionMemory[MemoryManager] contract
acquireExecutionMemory does...FIXME
Internally, acquireExecutionMemory varies per MemoryMode, i.e. ON_HEAP and OFF_HEAP.
.acquireExecutionMemory and MemoryMode [cols="1m,1m,1m",options="header",width="100%"] |=== | | ON_HEAP | OFF_HEAP
| executionPool | onHeapExecutionMemoryPool | offHeapExecutionMemoryPool
| storagePool | onHeapStorageMemoryPool | offHeapStorageMemoryPool
| storageRegionSize | onHeapStorageRegionSize | offHeapStorageMemory
| maxMemory | maxHeapMemory | maxOffHeapMemory |===
CAUTION: FIXME
== [[acquireStorageMemory]] acquireStorageMemory Method
[source, scala]¶
acquireStorageMemory( blockId: BlockId, numBytes: Long, memoryMode: MemoryMode): Boolean
NOTE: acquireStorageMemory is part of the memory:MemoryManager.md#acquireStorageMemory[MemoryManager] contract.
acquireStorageMemory has two modes of operation per memoryMode, i.e. MemoryMode.ON_HEAP or MemoryMode.OFF_HEAP, for execution and storage pools, and the maximum amount of memory to use.
CAUTION: FIXME Where are they used?
In MemoryMode.ON_HEAP, onHeapExecutionMemoryPool, onHeapStorageMemoryPool, and <
In MemoryMode.OFF_HEAP, offHeapExecutionMemoryPool, offHeapStorageMemoryPool, and maxOffHeapMemory are used.
CAUTION: FIXME What is the difference between them?
It makes sure that the requested number of bytes numBytes (for a block to store) fits the available memory. If it is not the case, you should see the following INFO message in the logs and the method returns false.
INFO Will not store [blockId] as the required space ([numBytes] bytes) exceeds our memory limit ([maxMemory] bytes)
If the requested number of bytes numBytes is greater than memoryFree in the storage pool, acquireStorageMemory will attempt to use the free memory from the execution pool.
NOTE: The storage pool can use the free memory from the execution pool.
It will take as much memory as required to fit numBytes from memoryFree in the execution pool (up to the whole free memory in the pool).
Ultimately, acquireStorageMemory requests the storage pool for numBytes for blockId.
[NOTE]¶
acquireStorageMemory is used when MemoryStore storage:MemoryStore.md#putBytes[acquires storage memory to putBytes] or storage:MemoryStore.md#putIteratorAsValues[putIteratorAsValues] and storage:MemoryStore.md#putIteratorAsBytes[putIteratorAsBytes].
It is also used internally when UnifiedMemoryManager <>.¶
== [[acquireUnrollMemory]] acquireUnrollMemory Method
NOTE: acquireUnrollMemory is part of the memory:MemoryManager.md#acquireUnrollMemory[MemoryManager] contract.
acquireUnrollMemory simply forwards all the calls to <
== [[maxOnHeapStorageMemory]] maxOnHeapStorageMemory Method
[source, scala]¶
maxOnHeapStorageMemory: Long¶
NOTE: maxOnHeapStorageMemory is part of the memory:MemoryManager.md#acquireExecutionMemory[MemoryManager] contract
maxOnHeapStorageMemory is the difference between maxHeapMemory of the UnifiedMemoryManager and the memory currently in use in onHeapExecutionMemoryPool execution memory pool.