Github user andrewor14 commented on a diff in the pull request:
https://github.com/apache/spark/pull/9559#discussion_r44357664
--- Diff: core/src/main/scala/org/apache/spark/scheduler/MapStatus.scala ---
@@ -121,6 +123,65 @@ private[spark] class CompressedMapStatus(
/**
* A [[MapStatus]] implementation that only stores the average size of
non-empty blocks,
+ * plus a hashset for tracking which blocks are empty(dense) /
non-empty(sparse).
+ * using a HashSet[Int] can save more memory usage than BitSet
+ *
+ * @param loc location where the task is being executed
+ * @param numNonEmptyBlocks the number of non-empty blocks
+ * @param markedBlocks a HashSet tracking which blocks are empty(dense) /
non-empty(sparse)
+ * @param avgSize average size of the non-empty blocks
+ */
+private[spark] class MapStatusTrackingEmptyBlocks private (
+ private[this] var loc: BlockManagerId,
+ private[this] var numNonEmptyBlocks: Int,
+ private[this] var markedBlocks: mutable.HashSet[Int],
+ private[this] var avgSize: Long,
+ private[this] var isSparse: Boolean)
+ extends MapStatus with Externalizable {
+
+ // loc could be null when the default constructor is called during
deserialization
+ require(loc == null || avgSize > 0 || numNonEmptyBlocks == 0,
+ "Average size can only be zero for map stages that produced no output")
+
+ protected def this() = this(null, -1, null, -1, false) // For
deserialization only
+
+ override def location: BlockManagerId = loc
+
+ override def getSizeForBlock(reduceId: Int): Long = {
+ if (isSparse ^ markedBlocks.contains(reduceId)) {
+ 0
+ } else {
+ avgSize
+ }
+ }
+
+ override def writeExternal(out: ObjectOutput): Unit =
Utils.tryOrIOException {
+ loc.writeExternal(out)
+ out.writeObject(markedBlocks)
+ out.writeLong(avgSize)
+ }
+
+ override def readExternal(in: ObjectInput): Unit =
Utils.tryOrIOException {
+ loc = BlockManagerId(in)
+ markedBlocks = new mutable.HashSet[Int]
+ markedBlocks = in.readObject().asInstanceOf[mutable.HashSet[Int]]
--- End diff --
did you mean to immediately override the assignment on the previous line?
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