Github user pwendell commented on a diff in the pull request: https://github.com/apache/spark/pull/1165#discussion_r14780288 --- 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. --- End diff -- This sentence is a little confusing. First, I don't think an array can be unfolded (unfolding refers to unrapping an iterator). So I think the first alternative should be something like "an array containing the entire contents of the block". For the second option, I'm not sure what it means to have a "partially unfolded iterator". I'll keep reading this PR and see if there is a better decsription.
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