Github user srowen commented on a diff in the pull request:
https://github.com/apache/spark/pull/17898#discussion_r115210488
--- Diff: core/src/main/scala/org/apache/spark/rdd/CartesianRDD.scala ---
@@ -72,8 +72,10 @@ class CartesianRDD[T: ClassTag, U: ClassTag](
override def compute(split: Partition, context: TaskContext):
Iterator[(T, U)] = {
val currSplit = split.asInstanceOf[CartesianPartition]
- for (x <- rdd1.iterator(currSplit.s1, context);
- y <- rdd2.iterator(currSplit.s2, context)) yield (x, y)
+ val groupSize = 500;
+ for (x <- rdd1.iterator(currSplit.s1, context).grouped(groupSize);
+ y <- rdd2.iterator(currSplit.s2, context).grouped(groupSize);
--- End diff --
Pardon, doesn't this change the type of the result? you're iterating over
groupings not elements, and emitting pairs of groups. As in below, but maybe
I'm missing something.
```
scala> val foo = List(1,2,3)
foo: List[Int] = List(1, 2, 3)
scala> val bar = List(4,5,6)
bar: List[Int] = List(4, 5, 6)
scala> for (x <- foo; y <- bar) yield (x, y)
res0: List[(Int, Int)] = List((1,4), (1,5), (1,6), (2,4), (2,5), (2,6),
(3,4), (3,5), (3,6))
scala> (for (x <- foo.grouped(2); y <- bar.grouped(2)) yield (x,
y)).foreach(println)
(List(1, 2),List(4, 5))
(List(1, 2),List(6))
(List(3),List(4, 5))
(List(3),List(6))
```
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