Spark Memory Manager

UnifiedMemoryManager:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111

// acquireStorageMemory
override def acquireStorageMemory(
      blockId: BlockId,
      numBytes: Long,
      memoryMode: MemoryMode): Boolean = synchronized {
    assertInvariants()
    assert(numBytes >= 0)
    val (executionPool, storagePool, maxMemory) = memoryMode match {
      case MemoryMode.ON_HEAP => (
        onHeapExecutionMemoryPool,
        onHeapStorageMemoryPool,
        maxOnHeapStorageMemory)
      case MemoryMode.OFF_HEAP => (
        offHeapExecutionMemoryPool,
        offHeapStorageMemoryPool,
        maxOffHeapStorageMemory)
    }
    if (numBytes > maxMemory) {
      // Fail fast if the block simply won't fit
      logInfo(s"Will not store $blockId as the required space ($numBytes bytes) exceeds our " +
        s"memory limit ($maxMemory bytes)")
      return false
    }
    if (numBytes > storagePool.memoryFree) {
      // There is not enough free memory in the storage pool, so try to borrow free memory from
      // the execution pool.
      val memoryBorrowedFromExecution = Math.min(executionPool.memoryFree,
        numBytes - storagePool.memoryFree)
      executionPool.decrementPoolSize(memoryBorrowedFromExecution)
      storagePool.incrementPoolSize(memoryBorrowedFromExecution)
    }
    storagePool.acquireMemory(blockId, numBytes)
  }



  /**
   * Try to acquire up to `numBytes` of execution memory for the current task and return the
   * number of bytes obtained, or 0 if none can be allocated.
   *
   * This call may block until there is enough free memory in some situations, to make sure each
   * task has a chance to ramp up to at least 1 / 2N of the total memory pool (where N is the # of
   * active tasks) before it is forced to spill. This can happen if the number of tasks increase
   * but an older task had a lot of memory already.
   */
  override private[memory] def acquireExecutionMemory(
      numBytes: Long,
      taskAttemptId: Long,
      memoryMode: MemoryMode): Long = synchronized {
    assertInvariants()
    assert(numBytes >= 0)
    val (executionPool, storagePool, storageRegionSize, maxMemory) = memoryMode match {
      case MemoryMode.ON_HEAP => (
        onHeapExecutionMemoryPool,
        onHeapStorageMemoryPool,
        onHeapStorageRegionSize,
        maxHeapMemory)
      case MemoryMode.OFF_HEAP => (
        offHeapExecutionMemoryPool,
        offHeapStorageMemoryPool,
        offHeapStorageMemory,
        maxOffHeapMemory)
    }

    /**
     * Grow the execution pool by evicting cached blocks, thereby shrinking the storage pool.
     *
     * When acquiring memory for a task, the execution pool may need to make multiple
     * attempts. Each attempt must be able to evict storage in case another task jumps in
     * and caches a large block between the attempts. This is called once per attempt.
     */
    def maybeGrowExecutionPool(extraMemoryNeeded: Long): Unit = {
      if (extraMemoryNeeded > 0) {
        // There is not enough free memory in the execution pool, so try to reclaim memory from
        // storage. We can reclaim any free memory from the storage pool. If the storage pool
        // has grown to become larger than `storageRegionSize`, we can evict blocks and reclaim
        // the memory that storage has borrowed from execution.
        val memoryReclaimableFromStorage = math.max(
          storagePool.memoryFree,
          storagePool.poolSize - storageRegionSize)
        if (memoryReclaimableFromStorage > 0) {
          // Only reclaim as much space as is necessary and available:
          val spaceToReclaim = storagePool.freeSpaceToShrinkPool(
            math.min(extraMemoryNeeded, memoryReclaimableFromStorage))
          storagePool.decrementPoolSize(spaceToReclaim)
          executionPool.incrementPoolSize(spaceToReclaim)
        }
      }
    }

    /**
     * The size the execution pool would have after evicting storage memory.
     *
     * The execution memory pool divides this quantity among the active tasks evenly to cap
     * the execution memory allocation for each task. It is important to keep this greater
     * than the execution pool size, which doesn't take into account potential memory that
     * could be freed by evicting storage. Otherwise we may hit SPARK-12155.
     *
     * Additionally, this quantity should be kept below `maxMemory` to arbitrate fairness
     * in execution memory allocation across tasks, Otherwise, a task may occupy more than
     * its fair share of execution memory, mistakenly thinking that other tasks can acquire
     * the portion of storage memory that cannot be evicted.
     */
    def computeMaxExecutionPoolSize(): Long = {
      maxMemory - math.min(storagePool.memoryUsed, storageRegionSize)
    }

    executionPool.acquireMemory(
      numBytes, taskAttemptId, maybeGrowExecutionPool, () => computeMaxExecutionPoolSize)
  }

StorageMemoryPool:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
/**
 * Acquire N bytes of storage memory for the given block, evicting existing ones if necessary.
 *
 * @param blockId the ID of the block we are acquiring storage memory for
 * @param numBytesToAcquire the size of this block
 * @param numBytesToFree the amount of space to be freed through evicting blocks
 * @return whether all N bytes were successfully granted.
 */
def acquireMemory(
    blockId: BlockId,
    numBytesToAcquire: Long,
    numBytesToFree: Long): Boolean = lock.synchronized {
  assert(numBytesToAcquire >= 0)
  assert(numBytesToFree >= 0)
  assert(memoryUsed <= poolSize)
  if (numBytesToFree > 0) {
    memoryStore.evictBlocksToFreeSpace(Some(blockId), numBytesToFree, memoryMode)
  }
  // NOTE: If the memory store evicts blocks, then those evictions will synchronously call
  // back into this StorageMemoryPool in order to free memory. Therefore, these variables
  // should have been updated.
  val enoughMemory = numBytesToAcquire <= memoryFree
  if (enoughMemory) {
    _memoryUsed += numBytesToAcquire
  }
  enoughMemory
}