Github user andrewor14 commented on a diff in the pull request:
https://github.com/apache/spark/pull/1165#discussion_r15091634
--- 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(
--- End diff --
I looked at this more closely and realized we can't do this easily. With a
type parameter, this returns an `Array[T]`. However, to put the result into
block manager, we need an `Array[Any]`, and we cannot easily cast from one to
another efficiently because arrays are not covariant.
Unfortunately, I think we need to keep this one as `Any`.
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