Github user mateiz commented on a diff in the pull request: https://github.com/apache/spark/pull/860#discussion_r13170395 --- Diff: core/src/main/scala/org/apache/spark/storage/BlockManager.scala --- @@ -329,8 +329,26 @@ private[spark] class BlockManager( * never deletes (recent) items. */ def getLocalFromDisk(blockId: BlockId, serializer: Serializer): Option[Iterator[Any]] = { - diskStore.getValues(blockId, serializer).orElse( - sys.error("Block " + blockId + " not found on disk, though it should be")) + + // Reducer may need to read many local shuffle blocks and will wrap them into Iterators + // at the beginning. The wrapping will cost some memory(compression instance + // initialization, etc.). Reducer read shuffle blocks one by one so we could do the + // wrapping lazily to save memory. + class LazyProxyIterator(f: => Iterator[Any]) extends Iterator[Any] { + + lazy val proxy = f + + override def hasNext: Boolean = proxy.hasNext + + override def next(): Any = proxy.next() --- End diff -- Small note on style, for this short a class you don't need an empty line before each method.
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