Github user pwendell commented on a diff in the pull request: https://github.com/apache/spark/pull/1165#discussion_r14809047 --- Diff: core/src/main/scala/org/apache/spark/storage/MemoryStore.scala --- @@ -141,6 +174,86 @@ private class MemoryStore(blockManager: BlockManager, maxMemory: Long) } /** + * Unfold the given block in memory safely. + * + * The safety of this operation refers to avoiding potential OOM exceptions caused by + * unfolding the entirety of the block in memory at once. This is achieved by periodically + * checking whether the memory restrictions for unfolding blocks are still satisfied, + * stopping immediately if not. This check is a safeguard against the scenario in which + * there is not enough free memory to accommodate the entirety of a single block. + * + * This method returns either a fully unfolded array or a partially unfolded iterator. + */ + def unfoldSafely( + blockId: BlockId, + values: Iterator[Any], + droppedBlocks: ArrayBuffer[(BlockId, BlockStatus)]) + : Either[Array[Any], Iterator[Any]] = { + + var count = 0 // The number of elements unfolded so far + var enoughMemory = true // Whether there is enough memory to unfold this block --- End diff -- nit: but I feel this would be better named `outOfMemory` and have it's opposite value. That way its clear that it is only ever mutated once, and when it's mutated the function short circuits.
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