Github user JoshRosen commented on a diff in the pull request:
https://github.com/apache/spark/pull/2866#discussion_r19308465
--- Diff: core/src/main/scala/org/apache/spark/scheduler/MapStatus.scala ---
@@ -112,35 +119,82 @@ private[spark] class CompressedMapStatus(
}
}
-
/**
- * A [[MapStatus]] implementation that only stores the average size of the
blocks.
+ * A [[MapStatus]] implementation that only stores the average size of
non-empty blocks,
+ * plus a bitmap for tracking which blocks are non-empty.
*
- * @param loc location where the task is being executed.
- * @param avgSize average size of all the blocks
+ * @param loc location where the task is being executed
+ * @param numNonEmptyBlocks the number of non-empty blocks
+ * @param emptyBlocks a bitmap tracking which blocks are empty
+ * @param avgSize average size of the non-empty blocks
*/
-private[spark] class HighlyCompressedMapStatus(
+private[spark] class HighlyCompressedMapStatus private (
private[this] var loc: BlockManagerId,
+ private[this] var numNonEmptyBlocks: Int,
+ private[this] var emptyBlocks: RoaringBitmap,
private[this] var avgSize: Long)
extends MapStatus with Externalizable {
- def this(loc: BlockManagerId, uncompressedSizes: Array[Long]) {
- this(loc, uncompressedSizes.sum / uncompressedSizes.length)
- }
+ require(loc == null || avgSize > 0 || numNonEmptyBlocks == 0,
--- End diff --
During the default constructor that's called in readExternal.
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