Github user aarondav commented on a diff in the pull request:
https://github.com/apache/spark/pull/1447#discussion_r15042631
--- Diff: core/src/main/scala/org/apache/spark/rdd/PairRDDFunctions.scala
---
@@ -216,17 +216,17 @@ class PairRDDFunctions[K, V](self: RDD[(K, V)])
def reducePartition(iter: Iterator[(K, V)]): Iterator[JHashMap[K, V]]
= {
val map = new JHashMap[K, V]
- iter.foreach { case (k, v) =>
- val old = map.get(k)
- map.put(k, if (old == null) v else func(old, v))
+ iter.foreach { pair =>
+ val old = map.get(pair._1)
--- End diff --
This I'm sure has been done a million times, but one more for good luck --
here is a `map { case (x, y) => x + y}` versus `foreach { xy => xy._1 + xy._2}`:
http://www.diffchecker.com/vtv6cptx
No new virtual function calls, but one new branch (trivially branch
predictable) and one new throw (which will never be invoked), and several
store/loads. (Perhaps I'm misreading the bytecode, but isn't `astore_2`
followed by `aload_2` a no-op?)
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