Github user shivaram commented on a diff in the pull request:
https://github.com/apache/spark/pull/6652#discussion_r31975752
--- Diff: core/src/main/scala/org/apache/spark/MapOutputTracker.scala ---
@@ -284,6 +291,54 @@ private[spark] class MapOutputTrackerMaster(conf:
SparkConf)
cachedSerializedStatuses.contains(shuffleId) ||
mapStatuses.contains(shuffleId)
}
+ /**
+ * Return a list of locations which have fraction of map output greater
than specified threshold.
+ *
+ * @param shuffleId id of the shuffle
+ * @param reducerId id of the reduce task
+ * @param numReducers total number of reducers in the shuffle
+ * @param fractionThreshold fraction of total map output size that a
location must have
+ * for it to be considered large.
+ *
+ * This method is not thread-safe
+ */
+ def getLocationsWithLargestOutputs(
+ shuffleId: Int,
+ reducerId: Int,
+ numReducers: Int,
+ fractionThreshold: Double)
+ : Option[Array[BlockManagerId]] = {
+
+ if (mapStatuses.contains(shuffleId)) {
+ // Pre-compute the top locations for each reducer and cache it
+ val statuses = mapStatuses(shuffleId)
+ if (statuses.nonEmpty) {
+ // HashMap to add up sizes of all blocks at the same location
+ val locs = new HashMap[BlockManagerId, Long]
+ var totalOutputSize = 0L
+ var mapIdx = 0
+ while (mapIdx < statuses.length) {
--- End diff --
Good idea. Done
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