Github user shivaram commented on a diff in the pull request:
https://github.com/apache/spark/pull/7461#discussion_r38597517
--- Diff: core/src/main/scala/org/apache/spark/rdd/RDD.scala ---
@@ -1080,6 +1080,21 @@ abstract class RDD[T: ClassTag](
var partiallyAggregated = mapPartitions(it =>
Iterator(aggregatePartition(it)))
var numPartitions = partiallyAggregated.partitions.length
val scale = math.max(math.ceil(math.pow(numPartitions, 1.0 /
depth)).toInt, 2)
+
+ // Do one level of aggregation based on executorId before starting
the tree
+ // NOTE: exclude the driver from list of executors
+ val numExecutors = math.max(context.getExecutorStorageStatus.length
- 1, 1)
+ partiallyAggregated = partiallyAggregated.mapPartitionsWithIndex {
case (idx, iter) =>
+ def isAllDigits(x: String) = x forall Character.isDigit
+ val execId = SparkEnv.get.executorId
+ if (isAllDigits(execId)) {
+ iter.map((execId.toInt, _))
+ } else {
+ iter.map((execId.hashCode, _))
--- End diff --
Yeah we don't necessarily need ints but its easy to reason about how
`hashCode` get balanced for ints (since the value of integer is the hashCode).
If you leave it as a String we will still have the same issue I pointed out
above with uneven tree structure
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