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[SPARK-8309] [CORE] Support for more than 12M items in OpenHashMap #6763

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[SPARK-8309] [CORE] Support for more than 12M items in OpenHashMap #6763

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SPARK-8309: Support for more than 12M items in OpenHashMap
SlavikBaranov Jun 11, 2015
f9284fd
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SlavikBaranov Jun 12, 2015
eaf1e68
Fixed failing test
SlavikBaranov Jun 12, 2015
4d5b954
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SlavikBaranov Jun 15, 2015
8557445
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SlavikBaranov Jun 16, 2015
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@SlavikBaranov
SlavikBaranov committed Jun 15, 2015
commit 4d5b9543b60611a54a1c1023783d3078f4b0b214
11 changes: 7 additions & 4 deletions core/src/main/scala/org/apache/spark/util/collection/OpenHashSet.scala
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Expand Up @@ -45,7 +45,8 @@ class OpenHashSet[@specialized(Long, Int) T: ClassTag](
loadFactor: Double)
extends Serializable {

require(initialCapacity <= (1 << 30), "Can't make capacity bigger than 2^30 elements")
require(initialCapacity <= OpenHashSet.MAX_CAPACITY,
s"Can't make capacity bigger than ${OpenHashSet.MAX_CAPACITY} elements")
require(initialCapacity >= 1, "Invalid initial capacity")
require(loadFactor < 1.0, "Load factor must be less than 1.0")
require(loadFactor > 0.0, "Load factor must be greater than 0.0")
Expand Down Expand Up @@ -223,7 +224,8 @@ class OpenHashSet[@specialized(Long, Int) T: ClassTag](
*/
private def rehash(k: T, allocateFunc: (Int) => Unit, moveFunc: (Int, Int) => Unit) {
val newCapacity = _capacity * 2
require(newCapacity <= (1 << 30), "Can't make capacity bigger than 2^30 elements")
require(newCapacity <= OpenHashSet.MAX_CAPACITY,
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@srowen srowen Jun 16, 2015

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I agree this is the theoretically largest number of elements that can be in the set. The failure will occur any time that twice the grow threshold exceeds MAX_CAPACITY, which can happen when the collection is less full than this. So I am actually not sure what's clearer here. Up to you.

I think we still have a little problem here, because when capacity reaches 2^30, twice that number becomes negative and newCapacity <= OpenHashSet.MAX_CAPACITY is true, still, because of overflow. Check whether the existing capacity is <= OpenHashSet.MAX_CAPACITY / 2 first?

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@SlavikBaranov SlavikBaranov Jun 16, 2015

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@srowen Integer overflow is not possible with current MAX_CAPACITY setting, since 2^31 is still positive number. Anyway, I've added check for positive capacity. IMO it's more clear way to guard against overflow.

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@srowen srowen Jun 16, 2015

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2^31 is positive, but it is not representable as a 32-bit signed int.

scala> val _capacity = 1 << 30
_capacity: Int = 1073741824

scala> val newCapacity = _capacity * 2
newCapacity: Int = -2147483648

So that's an important check.

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@SlavikBaranov SlavikBaranov Jun 16, 2015

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Oh, yes. Sorry :)

s"Can't contain more than ${(loadFactor * OpenHashSet.MAX_CAPACITY).toInt} elements")
allocateFunc(newCapacity)
val newBitset = new BitSet(newCapacity)
val newData = new Array[T](newCapacity)
Expand Down Expand Up @@ -277,9 +279,10 @@ class OpenHashSet[@specialized(Long, Int) T: ClassTag](
private[spark]
object OpenHashSet {

val MAX_CAPACITY = 1 << 30
val INVALID_POS = -1
val NONEXISTENCE_MASK = 0x80000000
val POSITION_MASK = 0x7FFFFFFF
val NONEXISTENCE_MASK = 1 << 31
val POSITION_MASK = (1 << 31) - 1

/**
* A set of specialized hash function implementation to avoid boxing hash code computation
Expand Down