Github user viirya commented on a diff in the pull request:
https://github.com/apache/spark/pull/15041#discussion_r79416925
--- Diff: core/src/main/scala/org/apache/spark/util/collection/Utils.scala
---
@@ -30,10 +34,22 @@ private[spark] object Utils {
* Returns the first K elements from the input as defined by the
specified implicit Ordering[T]
* and maintains the ordering.
*/
- def takeOrdered[T](input: Iterator[T], num: Int)(implicit ord:
Ordering[T]): Iterator[T] = {
- val ordering = new GuavaOrdering[T] {
- override def compare(l: T, r: T): Int = ord.compare(l, r)
+ def takeOrdered[T](input: Iterator[T], num: Int,
+ ser: Serializer = SparkEnv.get.serializer)(implicit ord:
Ordering[T]): Iterator[T] = {
+ val context = TaskContext.get()
+ if (context == null) {
+ val ordering = new GuavaOrdering[T] {
+ override def compare(l: T, r: T): Int = ord.compare(l, r)
+ }
+ ordering.leastOf(input.asJava, num).iterator.asScala
+ } else {
+ val sorter =
+ new ExternalSorter[T, Any, Any](context, None, None, Some(ord),
ser)
+ sorter.insertAll(input.map(x => (x, null)))
--- End diff --
I was thinking the value of this PR is to sort huge data and return small
top k. If `GuavaOrdering` can already do this, I would suspect the value of
this change. @cenyuhai What do you think?
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