Github user tdas commented on the pull request:
https://github.com/apache/spark/pull/6614#issuecomment-108802877
I think we need a different design. There is a way to count the elements in
the iterator without putting it into some intermediate buffer. Rather, the
iterator is going to be consumed any way (assuming StorageLevel is serialized)
by the block manager. The counting can be done while that is happening. To do
this you have to construct a special CountingIterator that wraps the original
iterator.
```
class CountingIterator[T: Manifest](iterator: Iterator[T]) extends
Iterator[T] {
var count = 0
def hasNext(): Boolean = iterator.hasNext
def next() = {
count+=1
iterator.next()
}
}
```
after iterating the original iterator via this counting iterator, you can
get the count of the records it had iterated through. This number can then
returned through BlockStoreResult object.
How does that sound?
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