Github user andrewor14 commented on a diff in the pull request:
https://github.com/apache/spark/pull/11534#discussion_r55615052
--- Diff: core/src/main/scala/org/apache/spark/storage/BlockManager.scala
---
@@ -428,77 +458,46 @@ private[spark] class BlockManager(
Option(
shuffleBlockResolver.getBlockData(blockId.asInstanceOf[ShuffleBlockId]).nioByteBuffer())
} else {
- doGetLocal(blockId, asBlockResult =
false).asInstanceOf[Option[ByteBuffer]]
- }
- }
-
- private def doGetLocal(blockId: BlockId, asBlockResult: Boolean):
Option[Any] = {
- blockInfoManager.lockForReading(blockId) match {
- case None =>
- logDebug(s"Block $blockId was not found")
- None
- case Some(info) =>
- doGetLocal(blockId, info, asBlockResult)
+ blockInfoManager.lockForReading(blockId) match {
+ case None =>
+ logDebug(s"Block $blockId was not found")
+ None
+ case Some(info) =>
+ Some(doGetLocalBytes(blockId, info))
+ }
}
}
/**
- * Get a local block from the block manager.
- * Assumes that the caller holds a read lock on the block.
+ * Get block from the local block manager as serialized bytes.
+ *
+ * Must be called while holding a read lock on the block.
+ * Releases the read lock upon exception; keeps the read lock upon
successful return.
*/
- private def doGetLocal(
- blockId: BlockId,
- info: BlockInfo,
- asBlockResult: Boolean): Option[Any] = {
+ private def doGetLocalBytes(blockId: BlockId, info: BlockInfo):
ByteBuffer = {
val level = info.level
logDebug(s"Level for block $blockId is $level")
-
- // Look for the block in memory
- if (level.useMemory) {
- logDebug(s"Getting block $blockId from memory")
- val result = if (asBlockResult) {
- memoryStore.getValues(blockId).map { iter =>
- val ci = CompletionIterator[Any, Iterator[Any]](iter,
releaseLock(blockId))
- new BlockResult(ci, DataReadMethod.Memory, info.size)
- }
+ // In order, try to read the serialized bytes from memory, then from
disk, then fall back to
+ // serializing in-memory objects, and, finally, throw an exception if
the block does not exist.
+ if (level.deserialized) {
+ // Try to avoid expensive serialization by reading a pre-serialized
copy from disk:
+ if (level.useDisk && diskStore.contains(blockId)) {
+ diskStore.getBytes(blockId)
--- End diff --
I would add a comment here saying don't bother putting it back in memory
here because we'd have to deserialize the data and that might be slow.
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